rough idle, stalling, loss of power.

dragonflyoffshore
1,790

Asked by dragonflyoffshore Nov 27, 2012 at 11:42 AM about the 1995 GMC Sierra 1500 K1500 SL 4WD Extended Cab Stepside SB

Question type: Maintenance & Repair

o2 sensor code 44 (lean)
Replaced: coolant temp sensor, tps, map sensor, fuel filter, and o2 sensor.
It will run normal on occasion but only lasts about 45 seconds or so. I don't think its the torque
converter, going into neutral doesn't seem to make a difference when it starts to stall, and will only
stall occasionally when stopped after warmed up.
takes longer to start when cold and will stall instantly after start up unless pressing the gas pedal.
once warm and somewhat stable idle will stall when put into gear.
any ideas?

195 Answers

tenspeed
57,055

Vacuum leaks can cause a lean condition and/or possibly a high idle. Check for cracked hoses a bad gasket or a faulty EGR or PCV Valve.

13 out of 13 people think this is helpful.
John Saffrahn
17,585

The only other thing that will cause a lean condition is low fuel pressure. A vacuum leak will be problematic at idle and go away with higher rpms. Low fuel pressure will get much worse at higher rpms.

16 out of 16 people think this is helpful.
dragonflyoffshore
1,790

Checked the pcv, a little dirty but working, replaced the elbow on the vacume line at the throttle body. Did have one cracked vacume line from the throttle body to the purge solenoid, also replaced. Seems to have plenty of vacume through out the system. Removed and inspected the egr valve, no excessive carbon build up and appears to be working properly, good vacume going into the solenoid, replaced the solenoid just for good measure. No results. At higher rpm seem almost like the exhaust is clogged but the cat has been bored, itll rev up but just wont really go. Today experienced a poping sound almost like a backfire from underneath. After the truck starts and is warm at a stable idle in park/neutral it'll rev up fine. But the stable idle won't last long, it'll idle low and rough. Mpg has decreased drastically and give off a rich smell when running.

66 out of 66 people think this is helpful.
You think this is helpful.
dragonflyoffshore
1,790

Bad hesitation off of the start, pumping the gas pedal helps to get her going. Pushing the pedal hard well bog it out and almost stall.

80 out of 80 people think this is helpful.
John Saffrahn
17,585

Have you tested fuel pressure, if so what is it when you turn the key on, while its idling, and while hitting the gas?

9 out of 9 people think this is helpful.
John Saffrahn
17,585

If the fuel pressure regulator diaphragm is ripped it can cause all these symptoms you are describing except the lean exhaust. That's why I'm curious as to what the fuel pressure is.

7 out of 7 people think this is helpful.
dragonflyoffshore
1,790

Haven't done it yet, but I will and get back to you. It's regulator is incorporated into the tbi correct?

5 out of 5 people think this is helpful.
John Saffrahn
17,585

Sorta it's "inside" the throttle body instead of having a vacuum hose running to it its like you said incorporated.

4 out of 4 people think this is helpful.
dragonflyoffshore
1,790

10-4 So if the pressure is good going in then I should be looking at the regulator, if the the pressure is bad obviously I'd should be looking at the fuel pump? I assume there really is no way of testing the the regulator itself considering it's incorporation.

4 out of 4 people think this is helpful.
John Saffrahn
17,585

The test is: 12-15 psi when the key is turned on and the pump will shut off within 3-5 seconds and the fuel pressure should drop to 12-13 psi. 11 being the bare minimum and 13 the Max. Once you start the truck the pressure should drop to about 10-11 when you rev the engine it may increase slightly but may not and if you do a road test it should be 12.5 - 13 psi max while fully accelerating. If it pressurizes good but drops below 11 when you initially turn the key on then I would suspect there's a good chance the diaphragm in the regulator has ruptured. If it doesn't put out good results to begin with then we could suspect the pump. Did you blow through the fuel filter after removing it? If there was excessive restriction it could have easily fried the pump due to the filter causing the fuel to "back up". I'm also curious as to what the 10-4 was, was that the result of the fuel pressure test? If so pull the air filter off and sniff the throttle body for a fuel smell. If the diaphragm has ruptured it will literally be like putting a hose with fuel into the intake and running it full. When it initially started to go it probably slowly flooded the engine to where it seemed to run ok but the excess fuel created a ton of carbon coating the O2 sensor. Since no air could pass through it, it gave a false lean reading. What color was your sensor when you removed it?

8 out of 8 people think this is helpful.
dragonflyoffshore
1,790

No..10-4 as in acknowledged, radio talk, sry I'm a boat captain. It's habit.

2 out of 2 people think this is helpful.
dragonflyoffshore
1,790

The old sensor wasn't bad looking, didn't appear to have any build up on it or the ports. Kind of a light ashy color..almost porcelain like, suspect it was the original. The truck only has 140k on it.

5 out of 5 people think this is helpful.
dragonflyoffshore
1,790

The new one still gives me the lean code 44.

4 out of 4 people think this is helpful.
John Saffrahn
17,585

The bad pump will cause it to run lean. But the regulator definitely won't. My truck had a bad pump from a clogged filter that was putting out about 8psi. It would idle ok but run like crap in gear and to drive it home I had to hit the gas then let off then hit it then let off. Luckily I only lived 2 miles from work at the time. I read it as 10 down to 4 not ten-four lol. Did you blow through that filter by any chance? Try spraying just a little Carb or brake cleaner into the throttle to see if the idle smooths out. Make sure the propellent is flammable, some of the new brake cleaners are non-flammable.

3 out of 3 people think this is helpful.
dragonflyoffshore
1,790

I did blow through it but don't remember the result..I still have the filter, l'll check it when I get home. I'll try it, I think I've got some starting fluid on the boat.

1 out of 1 people think this is helpful.
dragonflyoffshore
1,790

The old filter was free flowing, no restriction. Can't notice any excess fuel in the bowls with just the key on. Good spray on both injectors when giving throttle. Can't find test port for the fuel line. Only see two lines one in, one out.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

It will be on the larger of the two lines and either near the firewall or sometimes they put them down below. Mine was along the firewall.

1 out of 1 people think this is helpful.
dragonflyoffshore
1,790

No test port, used the gm in line adapter and tested after the fuel filter. Seem it's only getting about 2/3psi key on, 5psi while running. Sounds like we've got the problem.

3 out of 3 people think this is helpful.
dragonflyoffshore
1,790

Fuel pump it was, truck runs better then it ever has. Thanks for the help, it's much appreciated.

8 out of 8 people think this is helpful.
John Saffrahn
17,585

Awesome glad you got her fixed.

3 out of 3 people think this is helpful.
georgiacop1986
15

What type pump did you go with? I am having the exact same problem except I am at 342k miles on the all original drivetrain

1 out of 1 people think this is helpful.
John Saffrahn
17,585

I see 1986 in your name Georgia, that isn't by chance the year of your truck is it? 87+ are fuel injected with an in tank electrical pump, 86 and older like my current one are carbureted so it will be a mechanical pump on the side of the block. The symptoms may be the same but the issues will be completely different.

4 out of 4 people think this is helpful.
Alex Garcia
20

I'm having a similar problem, codes 22 tps sensor signal voltage low 33 map sensor signal out of range, high Are coming up but I've already changed out the map sensor and the tps seems to be working I disconnected it and idle went up to around 2 or 3 rpm and when I hooked it back up it went back down to a rough idle like its been doing. I changed the cap and rotor wires spark plugs and still nothing. Also I had to put a cat on it to pass inspection (state of TX) but it was a used one. Could a clogged cat be causing something like a domino effect and making these codes come up? Any help is highly appreciated!

2 out of 2 people think this is helpful.
Alex Lawrence
30

Check and see if your manfoild seƱor gone bad. It main just is to mix air/fuel. Mine ran like crap unroll I replaced the part It took forever to crank. Had to to keep your foot down on the pedal and acted very slugy and like to die. Soon as I replaced it ran like a champ

3 out of 3 people think this is helpful.
Alex Garcia
20

The thing is, I already replaced it. So in thinking its not getting power but haven't had a chance to check it out or even how to fix that.

geddy
20

I am having a problem. I would really appreciate some advise, I drive a 2010 gmc sierra 1500 with 57k on it, I got a code 454 thrown today,it said it was a FTP sensor, and now it is idling rough. when you put it in gear it falls on its face.

2 out of 2 people think this is helpful.
John Saffrahn
17,585

You try replacing the tank pressure sensor yet?

1 out of 1 people think this is helpful.
chrisdelia45
65

I have a 1996 GMC Sierra 5.0L. I recently replaced the fuel pump, fuel filter, PCV and spark plugs. This past week, my truck started stalling at stop streets or when my truck was parked and idling. Fuel pump relay is new. I checked voltages back to the fuel pump and they seem to be fine. At this point, my truck won't start. It cranks but there's no fuel supply. Assuming that all other fuel supply and voltage conditions are ok and that there's not a short, what could this be? ignition Control Module?

6 out of 6 people think this is helpful.
Ryan McClung
50

your fuel line between the pump and sending unit has come loose.

3 out of 3 people think this is helpful.
Marcgmc96
195

Hi I'm have a problem with my truck too. It's a 1996 Gmc k1500, 5.7. It was throwing a p0300 so I changed the plugs the cap and rotor and the wires. Fixed the code. Now my truck is idling rough at stop lights and stop signs. I put on the ac and it stalls out. Anyone have any suggestions?

8 out of 8 people think this is helpful.
John Saffrahn
17,585

Chris D, have you tested fuel pressure? Just because the pump is new doesn't mean it's good... Ryan/nutsack, if the effin fuel line was loose then he would be dumping fuel everywhere, just because you watched fast and the furious 5x in a row doesn't mean you know how too fix a car... Marc I will ask you the same thing I asked Chris, have you checked fuel pressure? Did none of you read any of the stuff I talked Dragonfly through on this post? Marc have you cleaned the throttle body and idle air control?

3 out of 3 people think this is helpful.
Marcgmc96
195

I have checked the fuel pressure it's normal. No I haven't check the throttle body or the idle air control. Thanks a lot. I'll check it tomorrow.

Ryan McClung
50

John cutback do you know these trucks. If u read my. answer u would know that the fuel pump and sending unit are both in the tank therefore the hose that splits or comes undone is in the tank also. Not saying this is the case. And yes I do believe I know these trucks a lil better than u.***Oldfart###stuckinhisways##///!!!!

2 out of 2 people think this is helpful.
foxhound87
0

I had. a similar problem I heard a loud popping sound and a really rough bad idel on my foxbody I changed the sparkplugs and now the sound is gone as well as the rough idel

John Saffrahn
17,585

The pump sits in a cradle on the sending unit, the little rubber connector line is wedged between the steel fuel line and pump, the sock filter keeps the pump from going anywhere. If the line was loose then that means the pump isn't in that cradle which means the sock has fallen off, the pump has slid further into that rubber line so it had room to come up and out of that cradle and it now has nothing holding it onto that line. Is that what you're saying?

2 out of 2 people think this is helpful.
Estep76
260

I have a 1990 chevy k1500, ive had a hell of a time with it. Its running like its out of time. So i timed it and their was no change. It is hard to start i have to spray carb cleaner into the intake for it to start. When its cold And it will idle in park and neutral but if u put it in drive or reverse it stalls. I cant get it to go faster than 40mph and it wants to choke its self out it seems when i give it gas. it will rev up but when u stomp it down it misses and sputters like it getting too much back pressure or like i said choking its self out. It will only run with the map sensor unplugged also. If i could get some advise it would

21 out of 21 people think this is helpful.
Estep76
260

Be greatly appreciated thanks

1 out of 1 people think this is helpful.
Estep76
260

I have changed the computer fuel pump fuel filter distributor plug wires fuel pump relay. idle air control. map sensor throttle position sensor awile back when it messed up the first time it was the pick up coil and i chandged all that other stuff trying to figure out that problem. Now its messing up agin. And idk what the problem is.

4 out of 4 people think this is helpful.
John Saffrahn
17,585

Any codes? How many of the things mentioned above have you checked?

1 out of 1 people think this is helpful.
firemedic44
20

John, hey bud. You seem like you know ur shit. Need some advice. Got a 1990 Chevy CK 350. Wrecked the family car and its all we got now. Anyway truck was great but started backfiring and stalling etc. Then broke down, sat,got towed, etc. Got it back now. I'm in no way a mechanic but I do have good common sense Changed plugs, fuel filter and fuel pump. Cranks but will not turn over. Smell no gas either when cranking. Whats next? How do I get a code tester cheap? What do you advise...Help please

1 out of 1 people think this is helpful.
Sean Mccoy
50

is the pump getting power? have a helper turn the key on, and listen at the fuel tank inlet for the pump to operate for about two seconds. if it doesnt buzz, then you may not be getting power. check all fuses, and swap fuel pump relay with another one that is known good. next would be to check fuel pressure. that year the spec for fuel pressure on a tbi is 9-13 psi. you will need an inline pressure checker as there is no port on the line. the exception to this is if the vehicle is a R or V body designation. those didnt change until '92, so they may still be carbureted, so procedure will change.

1 out of 1 people think this is helpful.
Sean Mccoy
50

also, you need a piece of wire bout three inches long to make a code checker. under the dash below the steering column is the aldl connector. it consists of two horizontal rows of square holes, bout eight in each. using your wire, jumper from the top right hole to the next hole to the left. this will cause the check engine light to flash. do the procedure with the key in the on position, with engine off. (i know, it wont start anyway, lol). each code will flash three times, with code 12 ( one flash, pause, two flashes) being first. any stored codes will follow. after all codes have been flashed, it will start over with 12.

4 out of 4 people think this is helpful.
John Saffrahn
17,585

Paper clip will work if you don't have any spare wire laying around, Sean posted pretty much exactly what I would have posted.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

If you know how to use an ohm meter then you could also test the continuity of the whole fuel pump wiring at the relay also. Find the constant 12V power supply to the relay and check resistance from the hole kitty corner to that 12V to battery ground. OL means something is disconnected. There shouldn't be a lot of resistance, in the teens at the most, high resistance could be a burnt wire, burnt connector, bad ground.

2 out of 2 people think this is helpful.
Marcgmc96
195

Ok so I'm back. I have a 1996 GMC k1500 5.7 4x4. My truck has a bad idle in drive and park. Nutral and reverse it idels fine. Also when I come up the a stop light it wants to die and has died couple time. I have changed my cap and rotor, MAP, idle control valve, spark plugs, wires. Mass air flow sensor, fuel filter. I have checked the compression for a burnt valve and I have checked the fuel pressure. I can't think of anything else. The only thing left I can think of is a wiring problem. I pulled the wire to the mass air flow sensor and nothing changed. I put a bag on the air filter to see if I could get a change in idle. ( a buddy told me to.) also I have checked for vacumme leaks with brake clean. Is there anything else that u can think of? I just wanna get the idel better to sell it.

7 out of 7 people think this is helpful.
You think this is helpful.
Marcgmc96
195

Oh and when I'm driving down the road at high RPM's it fine. It has power when needed and run like it's off the show room floor. Just at idel it does this.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Does it idle rough when it's warm our at all times? Check engine light on? Have you cleaned the throttle body?

3 out of 3 people think this is helpful.
Marcgmc96
195

In the morning it idels a little more rougher. When it warms up its not as bad, but still rough. I have cleaned my throttle body when I changed my idel control valve.

2 out of 2 people think this is helpful.
firemedic44
20

Thanks for advice. Changed fuel pump relay today. My manual only shows one relay on the passenger side fire wall but there is another right beside it with same serial #s. Any idea what it is? I exchanged fuel pump even though it was new. I wasnt hearing it. Tested for power in the connector as I turned on key and the light came on but it seemed a little dull. (circuit tester) all I had. And I dont expect to be taught in a day but I'm new to this so my lingo may be wrong. Also at the risk of sounding ignorant where will I see the code numbers displayed. Thanks to all.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

The check engine light itself will flash, it will flash a two digit code starting with 12 then it will flash the next stored code in ascending order of stored codes. You have to count the flashes, a code 44 will be four flashes followed by a brief pause then four more, it repeats every code three times including the number 12, if it keeps flashing 12 then that means no codes are stored. Not sure what the other relay is for, unplug it and see what quits working. Possibly the blower fan relay for the high setting. Use that test light to bridge the fuel pump relay to see if you have a complete circuit, one of those prongs should receive constant power, jump that one to the one kitty corner to it.

3 out of 3 people think this is helpful.
John Saffrahn
17,585

Marc where do you live and how much are you asking for the truck as is?

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Marc what is the rpm of the idle? There is a possibility also that the distributor isn't tight and when you pulled the cap it may have turned a bit causing the ignition timing to change.

2 out of 2 people think this is helpful.
Marcgmc96
195

john I live in Ca. I was think of selling it for $3,000. I has a 4" trail master lift with 35x13.5x 15 toyo MT. With weld rims. It's a ext cab.

Marcgmc96
195

Also john the idle is at 400 then it bounces to 1500. Seems like it's starving for fuel.

John Saffrahn
17,585

400 is way low, check alternator output at an AutoZone, also check engine vacuum at one of the ports, could be a stuck open egr valve, did you get a chance to check the distributor? I live in Indianapolis, too far of a drive.

1 out of 1 people think this is helpful.
Marcgmc96
195

I haven't I worked 6 hours of Over time today on top of my 10 hour reg day. I'll check tomorrow. How do check the engine vacuum? I know u said a port. Does one of the vacumm lines have a port?

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Follow any one of the lines up to the throttle body, the metal nipple that the line slides over is a port, test from one of the ports by disconnecting one if the lines and put a T connector in and hook up a vacuum gauge to it, or unplug one of them and test from it if the vacuum is good then hook that one back up and unplug the next and test there, if the vacuum is still good then no leaks.. if the vacuum is low then just start gently squeezing the vacuum lines one by one until the vacuum comes up, that is the leaking line, let go and go further down the line and pinch it off, if the vacuum comes up then the leak is further down, keep going. Carburetor cleaner is a bad idea, I saw a guy soak down an engine bay looking for a vacuum leak because an engine had a miss and was shaking, he found out the hard way that the spark plug wire was burnt through and grounding to the side of the block. Luckily the engine was hot and the fans were on so most of the carb cleaner had dissipated and nothing was damaged. Propane is a better way to go. Even an arc inside the alternator could do the same with the cleaner if it were an accidental bad spray. Just be cautious with flammable propellants.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Also check to see if there is an idle adjustment screw on a bracket near the throttle cable connection point, if so does giving the engine just a tad more gas help, maybe you could adjust that screw a tad until it makes it run smoother...

1 out of 1 people think this is helpful.
Wildfire Day
80

John need ur advice plz

1 out of 1 people think this is helpful.
Wildfire Day
80

1995 gmc seirra pickup it idles fine while in park however when going three or four blocks it loses power and starts to act like a diesel truck. Tried replacing throttle position sensor, engine control temputure sensor, and fuel injector, what else is there to try?

7 out of 7 people think this is helpful.
Mgmprofits
10

Testing

1 out of 1 people think this is helpful.
Mgmprofits
10

Hello there John, Thanks for all your replies and help here. It sounds like you know what you're talking about. I don't know if you know about Lexus at all, but I have a 94 SC400 that has been an absolute NIGHTMARE trying to figure out the problem. I haven't brought it into Lexus yet because they charge a fortune for every little thing and I don't trust the dealers around here after getting ripped off by them in the past. But I have brought it to my trusted mechanics who haven't been able to figure it out. If you have ANY ideas, on what I should try next it would be greatly appreciated. Here are my symptoms- The check engine light is usually on, but it turns randomly and back on again at times. It was not on at all when I bought the car, but after I brought it into the mechanic (for stalling out in a drive through and it WOULD start back up but then stall out right away again. Then it started fine after sitting for a few hours. But I had it towed in anyway. Also in the MORNINGS only when it was cold, it would take a few seconds to crank/start before it started. But if I turned the key to the drive position for 10 seconds before trying to start it, then it would start right away. I was told that meant I had a fuel pump issue) So I figured the dying out was my fuel pump going bad so I have it towed to the shop as I said (Please bare with me here as the list of symptoms is kind of long and crazy but I need to get to the bottom of this) and the shop tells me that my fuel pump is OK, it tested fine they said under the pressure test. But I hear these tests are not always accurate? I still suspect it could be the feul pump but I need to tell you my issues and how the car progessively is getting worse with new symptoms. Everytime I bring it into the shop they tell me I need a new part, which has not fixed the problem. First they told me I needed a Crankshaft Positiion Sensor, because they said the Computer code told them I needed it. Well, I am 99% SURE I did NOT need that sensor. Never had any symptoms of a bad crankshaft sensor. My car always started up everytime, it never FAILED to start, which is what happens when that sensor is bad. So I fear the computer might be giving the wrong codes. I had an idea that MAYBE my problems are tied to a bad Computer in the car? Should I try to replace the main ECU for the car? I recently replaced the FUEL PUMP ECU, the 2nd time I brought the car in, as it DIED again, same symptoms, stalled out and it WOULD start again right away, but then die right away. I kept trying to get it to stay running and I could not. So I knew I got ripped off on that Crankshaft Posiiton Sensor, as it never fixed the problem. Also I forgot to mention that AFTER they put that sensor in, my car had a NEW problem (which they denied causing, but it NEVER did this before I brought it to the shop) The new problem, which is really bugging me, is that when the Car is COLD, it STUTTERS AND BUCKS EXTREMELY BADLY. Infact the RPM's are hard to get over 2000 RPM. And it won't go faster than 20 MPH when it's cold. As it starts to warm up, it stop bucking so much unless I hit the gas harder, then it still does it. So, the symptoms are COLD- I barely hit the gas and it bucks/Stutters. HOT- I can hit the gas LIGHTLY and it won't stutter and I can drive over 20 MPH. lol But this is soooo annoying that they have done this to my car. It all started after they put that CPS Sensor in (Crankshaft position sensor) which I have no idea if it's connected to that or not. I think they might of messed up some wires or created a vacuum leak or something in the process of their repair. So I bring it in again, and the 2nd time they tell me I needed a FUEL PUMP ECU and that is why my car is stalling. So, I bought one and had a Fuel pump ECU installed, and since then (This was only 2 weeks ago) the car has NOT stalled yet, but I fear that it will again and that they diagnosed it wrong again. Who knows. But I am more worried about this BUCKING/STUTTERING problem, as the car is basically undrivable until it gets warmed up. Even then it doesn't seem to run as good as I can never hit the gas hard to speed up or it will bog down again. Another thing which I find strange is that my Check Engline Light was NEVER on before I brought the car in there, and it even had a SMOG cert when I bought it. I think they may have messed it up and caused the light to come on (that would mean they are dishonest though, since they told me my Light bulb was just burned out and they even charged me for a new bulb) I believe they are honest, as the reviews say they are and I never had a bad experience with them. I think they just have NO clue how to fix a Lexus. I am leaning towards something to do with the MAF sensor (although they claimed they checked this and it was good, but it could still be the wires or something right?) I also have a REALLY BAD SMELL (Not rotton eggs) coming from the exaust. Smells like I am running rich or something. There is definitely some kind of problem(s) going on with the car and as I said before the Check engline light turned off for a BIT when they installed the Fuel Pump ECU (Also they claimed they changed the spark plug wires for me as well, since they said those were bad, but that did nothing to help this problem) And they said they checked out my Spark Plugs and those were good. PLEASE HELP!! Anyone, if you know what part I should try to replace next let me know. Should I try the fuel pump itself? even though it passed the pressure test and they assured me it is not the pump? I think it very well could be from what Ive read online. Or should I try replacing the entire MAIN CPU for the car? Because I can get one on Ebay for $30 so it would be really cheap, and I could have them put it in and see if maybe that's it. They have run out of ideas themselves, they said they have no clue what is causing this. Which I hate to hear supposed car experts say that. I really need to fix this before it really damages my engine. Also I am sure it won't pass smog like this. I just put over 5k into this car and now I have to get another smog test in a couple of months. If I can't figure out what's wrong I will have to lose the car and all the money I put into it. Nobody would even think about buying it in this kind of condition.

Forrest Adams
20

I had the same problem and the little chunk of rubber hose between my fuel pump and pickup tube had a hole in it after I replaced that all my problems went away... you have to drop the gas tank for this job..

2 out of 2 people think this is helpful.
Joshsk
20

Does your car only do that when hot? I have similar problems. When cold, it accelerates like a champ, but after driving for a few miles in this heat, it starts to act up. From a stop, I can't rev it too high or else it cuts out real hard, as if the gear popped out. When in motion and constant, it'll sputter for a fraction of a second, 2000 mustang please help

2 out of 2 people think this is helpful.
italianrob
10

Hi John.. I have read the past with dragonfly at the top here.. I'm experiencing these same problems as him. . But I don't have. Or can find this gm inline fuel pressure tester. .I can however tell you that when I cleaned out the throttle body it ran smooth and i could Rev it up with no rough idle or bog..i stop spraying and it bogs stalls or back fires out the throttle body.flames as well .. I have done the other checks you discussed. Changed rotor cap plugs wires . vacumn line. cleaned egr valve haven't done the pcv valve.. Going to change the fuel filter today. . My question is about the idle smooth while spraying ..

italianrob
10

Changed fuel filter was severely plugged ... started up instantly but idle is fine just not so good when Rev it up.. sounds like back fire a couple times while reving engine. .. Oh It's a 1989 v8 305 5.0 gmc vandura 2500

John Saffrahn
17,585

The spray smoothing out the rough rpm is an indication of the engine running lean, could be low fuel pressure, could be a vacuum leak. With it running rough at an idle and smoothing out at a higher rpm is a general sign of a vacuum leak. The larger amount of air and fuel mixing at a higher rpm prevents the small vacuum leak from altering the air fuel ratio. Idling smooth and running rough at higher rpm is generally a low fuel supply issue, it is demanding more fuel but isn't receiving it. Since the fuel pressure regulator is in the intake that can be ruled out. Having a plugged fuel filter will cause the pump to work harder and prevent fuel flow which is the pumps main heat dissipation source, the added work load and heat can cause the pump to go bad very quickly. http://www.sjdiscounttools.com/ta3 7650.html Check the link for spaces when you copy and paste, this temporarily replaces the filter to do fuel pressure testing.

1 out of 1 people think this is helpful.
John Saffrahn
17,585

http://www.actron.com/product_det ail.php?pid=16175 You can see the little adapter piece in the top left, this one ties into the fuel line at the throttle body.

1 out of 1 people think this is helpful.
wierzchowski
0

Hey john my name's Matt and I have a 95 Chevy k1500 4x4 with the 5.7l and my problem is that when I start my truck it idled rough right when it goes but then catchs itself and then idles at the right rpm and if I hold the rpms at a specific area they will hold but when I put it in gear reverse or drive the truck idles low and shuts itself off I replaced the plugs the whole distrubtor made sure it was in time. Also the map sensor ,the tps, iacv, egr, egr vacuum solenoid, no vacuum leaks cleaned tbi and intake out and the only thing I can think is wrong is the fuel pump or the fuel pressure regulator bladder the redish/Orange seal but I don't have a compression test tool so iam at a stuck point and I do have a check engine light on and don't have the ob1 reader so will try the paperclip or wire trick and iam leaning towards the fuel pump. Please let me know what you think on that

John Saffrahn
17,585

Rent a fuel pressure tester from AutoZone.

2 out of 2 people think this is helpful.
Thomas Campbell
0

hey john i stay in indianapolis and have the above rough idle at any rpm below 900 and hard cold start issues with carbureted 1968 307. my question is will a combination of a toque converter out of a v6 700r4 stall be too low (1000-1100) a oem alternator from 3.8 v6 cause these issues along with stalling at light and when shifting into gear. symptoms- loss of stable vacuum reading when shifted into gear-drop off in rpm from idle to Rev= 500. advancing distributor helps without causing pinging but the advancement causes "kickback" on starter(replaced twice 2nd time with shims) HELP!!!

John Saffrahn
17,585

Hard telling, I really don't know. Idle seems a little low to begin with but like I said idk.

1 out of 1 people think this is helpful.
biggamer
30

Hi john I have been reading your answers and u seem to know what u are talking about. My name is brad and I have a 1997 gma sierra 4x4 5.7L. I have put a new rear end a new tranny a new fuel filter and a new battery. My issues... it is giving me a really hard time starting, my lights radio ex all come on. And it roles over just acts like it isn't fireering but the minute I hook jumper cables up it starts.Once started it idles fine and drives fine but when I put my foot to the floor it bogs out and when I back off the peddle it catches any ideas of What it could be or were I should start?

3 out of 3 people think this is helpful.
John Saffrahn
17,585

Test fuel pressure, it should be 11- 13psi before starting, 10-11.5 at idle and 11-13 under hard acceleration. Have the coil tested. Check the electrical timing. Check your alternator output while idling, your truck only needs about 9.5-10 volts in a good battery to start and run but it will do both roughly. If the alternator is only putting out 10 volts it may be preventing both the fuel pump and ignition from working at full capacity. It will also prevent the battery from ever getting a full charge causing a hard start.start with whatever is easiest for you, AutoZone rents out a fuel pressure tester you will have to get the inline adapter that temporarily replaces the fuel filter for testing.

2 out of 2 people think this is helpful.
biggamer
30

Thank you john I will look into these things and will let you no the out come of the results once done. If I have any more questions I will be sure to get a hold of you again thank you

John Saffrahn
17,585

Yup

1 out of 1 people think this is helpful.
Vildobottomdiva
45

Ok Im new to this forum but really confused about what my truck is doing. I have a 1995 GMC K1500 4x4 Z71. About 3 weeks ago my fuel pump went out on my truck. I removed the tank removed the old fuel pump and replaced it with a new one. I cleaned my tank really good before installing the new one. I also replaced the fuel filter on the frame under the driver door. About a week ago it started acting all kinds of crazy. At start up when cold it runs like a top for about 1 to 2 miles. Once the engine gets heated up it starts spitting and sputtering. If you baby the gas it goes on but still cutting out. If you cram it to the floor it picks up fuel and goes on like a top but then when you let off it then it goes back to the spitting and sputtering. My son put it on a ob1 scanner and it registered the code for the EGR but he said he didn't think that was happening because he took my EGR out and looked fine and he could even blow through it and it wasn't stopped up. So I took it to a local shop here and had it put on a machine and they informed me it was the map sensor so I changed that. Still doing the same thing. However when you unplug the map sensor it runs like a top at idle and in drive/reverse with my foot on the brake. I was standing there when they put the fuel pressure gauge on it and at start up/ idle/ and in drive it registered 10 psi. It never changed. The shop told me if the map sensor didn't fix it then it could be the computer. I just don't really believe that. I truly feel it would be another sensor somewhere that the shop missed. After it warms up if it is sitting idling it runs rough as crap and then dies. Once it dies I smell some nasty fart smell or something rotten. I am so confused with all this. Sometimes my service engine light will come on and when it does my truck runs like a top but when it resets itself it starts running rough again like it losing fuel. Just today on the way to work it sat and idled for a few minutes and started running a lil warm from where it usually runs. Could all this be caused from a coolant temp sensor. I am so confused with all this crap. I HATE SENSORS!! Anyones help would be appreciated. Thanks Tam

italianrob
10

That rotten nasty smell.. Does it smell like Sulphur if so it would be a plugged up/melted catylinic converter getting red hot....

Vildobottomdiva
45

Thanks but my truck doesn't have a cat it was cut off and new cherry bombs put on. but i figured it out and it was a broken ground wire from the frame to.the back of the block and an o2 sensor that fixed it. Im not confused aanymore lol she runs like atop again. thanks for all ur answers though.

John Saffrahn
17,585

O2 sensor was keeping it in open loop mode flooding the engine out at low idle.

2 out of 2 people think this is helpful.
alexamador
15

Hi i have a 96 chevy c1500 with a 5.7 liter and tpi. I resently installed distruburator cap , rotor,camshaft position sensor, ignition coil, pcv valve ,wires,spark plugs, bank 1 sensor 2 oxygen sensor ,mass airflow system,and fuel filter. My check engine light was on and it pulled those code so i did all the work myself to save some cash. And now my truck is back fireing when its at 1500 rpm. Can anyone help ????

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Sounds like you crossed some wires, it's a pretty common mistake. Double check that you have the wires in the correct order on the cap

1 out of 1 people think this is helpful.
Certy
10

Dpfe sensor

1 out of 1 people think this is helpful.
John Saffrahn
17,585

I can assure you none of these GM vehicles have junk Ford parts like a dpfe sensor or fuel pump inertia safety switch.

alexamador
15

Thanks guys

bassmaster63
10

hi i have a 1995 gmc 1500 4 by 4 with a 5.7 .does not do it all the time but runs great while warming up for about 5 to 10 minutes then goes into a rich idle ,but does come out of it some times going down the road at low speeds it acts like it hanging there until you step on fuel pop out of throttle body and goes lots of times will come into a skip then go away.this thing making me pull my hair out tryig figure out whats going on dont have much more to pull out

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Sounds like it's stuck in open loop, What have you done testing/replacing so far?

1 out of 1 people think this is helpful.
Acheron61
0

Mr. John, Here is an oddball one for you. 95 K1500, 5.7. Truck runs great at idle and at above 1200rpm. When between 700-1200 the truck falls flat on its face. Coming to stop lights it falls flat on its face. New=spark plugs, wires, rotor button, dist cap, all new vacuum lines, throttle body spacer and gaskets, IAC, cleaned tbi. Maf/map sensor is good. With the EGR solenoid disconnected from tbi the truck runs like a champ, no issues at all. But if you plug the line coming from the tbi to that solenoid and give it gas, it craps out. Fuel pressure is right up to tbi. Would this be the regulator in the tbi? going to adjust the IAC and TPS this morning. Any ideas?

Acheron61
0

BTW, I did try replacing that solenoid and it did no good whatsoever.

John Saffrahn
17,585

Have you checked ignition timing and to see if the advancement on the distributor is working properly?

ChevyMade
0

I have a 1991 Sierra fresh motor out of nowhere started sputtering under load at any rpm or mph when accelerating and will not go over 35 mph and ppd I can tell the exhaust sounds lean. Also smells like it's running really rich so I rebuilt the throttle body new map sensor new iac new coolant temp sensor new cats. I have no clue what it could be now any help would be greatly appreciated

John Saffrahn
17,585

Have you done any kind of diagnosing? Fuel pressure, ignition timing, check for a misfire, pulled any codes?

ChevyMade
0

No I'm taking it to my mechanic tomorrow to try to pull codes and I'm hopefully going to autozone to get a fuel pressure reader. But I pulled plugs on both sides and both are charred black from the gas I assume I can even smell it in my oil.

Jlpruitt81
0

I have a 99 Chevy suburban k1500 5.7 4wheel drive. I am also having idle troubles. I'm only do basic mechanic stuff so when my truck started dying at idle I replaced the fuel filter, spark plugs, and check the PVC valve. At this point I have ran out of daylight to work on it but I don't know where I should start tomorrow. My truck when I initially start it up won't start unless I give it some gas to aid it at which point it will run rough idle around 500. As long as I have high Rpms the truck will keep going but it will die as soon as I slow down for a light or stop. I plan on checking on the erc sensor and trying to figure out what my psi is at but what else can I be looking at? ( also doesn't seem to be a vacuum leak but I could be wrong.)

Jlpruitt81
0

Oh also advance ran diagnostics and only code pulled was p300 multiple misfires which is why I replaced the spark plugs. Also keep catching a whiff of oil n gas m

Jlpruitt81
0

Mix as well

John Saffrahn
17,585

Definitely check fuel pressure, could be an injector stuck open or pressure regulator diaphragm ripped, could be idle air control solenoid is stuck or egr stuck open. Doubt it's the coil since it goes away at a higher rpm.

aarona74
45

Hi john seems like you are the guy to talk to on here I've read many posts very good input. I'm working on a 92 ford f150 with the 5.0 and this truck runs great when the engine is cold good shifting etc. But after the engine warms up it sounds like its missing and backfires and choughs and it also shifts early now while this is happening I can put the transmission in park or neutral and rev the motor up and it sounds fine with no miss etc. But as soon as I put back into drive just misses and wants to die. Please please help thanks Aaron from Illinois

John Saffrahn
17,585

You scan it for codes? Sounds like it may be stuck in open loop. Do you also smell gas and notice your gas mileage has gone down? That is a sure sign of open loop.

aarona74
45

Thanks yes my gas mileage is horrible and it seems like its getting way too much fuel where you will try to get it going down the road pumping the gas as it is stalling and backfiring what is a open loop

John Saffrahn
17,585

It makes cold starting and cold running easier, it's the computers version of choke. You would need a scanner capable of reading obd1 live data to see if it's in open out closed loop, engine coolant temp and oxygen sensors are what control the loop status. When the engine is up to temp and the oxygen sensors are warned up and cycling properly it will go to closed loop. Bad engine coolant temp sensor, cold running engine, or bad oxygen sensor is usually the culprit for this. There are other possibilities but they are less likely. Open loop can cause the engine to run colder due to the extra fuel being used so just because your temp gauge is reading low it didn't mean the engine being cold is the cause.

John Saffrahn
17,585

Typo, out should be or, "open or closed loop"

aarona74
45

actually true my engine temp gauge in the truck always runs low never gets past the n on normal on the gauge although the engine is plenty warm even after driving for 15 to 20 minutes

onixmydog
0

hi I have a 2005 jeep liberty when I start my jeep it idles high then slowly goes down. when I go to drive it, it starts to vibrate an seems like it wants to stall. I had my water pump replaced yesterday

aarona74
45

Hi john I was curious if you can check the o2 sensor or temperature sensor by chance with a multimeter or such thanks

John Saffrahn
17,585

Yes you can but it involves removing it from the exhaust and you need a torch and a second person would make testing it a lot easier.

aarona74
45

Oh OK I have a second set of hands if needed.

aarona74
45

Would you happen to know how I could pull the codes on my 92 f150 efi 5.0 thanks

John Saffrahn
17,585

Phone http://m.youtube.com/watch?feature=youtu.be&v=QM2jO0_Cah0 Computer https://www.youtube.com/watch?feature=youtu.be&v=QM2jO0_Cah0

John Saffrahn
17,585

Obd1 code scanner, Ford usually put the plug either under the dash or under the hood by the firewall, passengers side near the blower motor, if it isn't there then you will understand why I don't like Ford.

aarona74
45

Yeah thanks mine is under the hood labeled EEC TEST I thought I needed a obd2 tester from some of the information I've came across

aarona74
45

I tried pulling codes and my check engine light never came on any suggestions. When I bought the truck the check engine light was on and now it hasn't been on since?

John Saffrahn
17,585

It's obd1 not obd2 some scanners do both, the scanner AutoZone usually uses is obd2 only. Obd2 has a mandatory plug location under the steering wheel, same place gm has pot it since day 1. Turn your key on and see if your check engine light is on while your engine is not running, if the light is on then the bulb is working and it's likely no codes are stored if you used the correct scanner or jumper wire method. If the light doesn't come on then you may have a stored code or you may not and you won't be able to pull codes with the jumper wire method. A bad oxygen sensor on an obd1 vehicle won't always trip a code. If it is reading like it's still cold then it will keep the computer in open loop. A bad upstream oxygen sensor will always keep the engine in open loop.

aarona74
45

Oh OK I see thank you very much for all your great answers I really appreciate it. Just out of curiosity if the truck only has one oxygen sensor but running dual exhaust would this mess with how it runs since one side of the exhaust has a o2 sensor and the other side does not?

John Saffrahn
17,585

Usually if it only has one from the factory they put it where it will pick up both banks like at the y pipe or just before the catalytic converter. Then again it is a Ford, if it only came with one from the factory and it's only on one bank then issues it would have caused would have been day one. So they made it work if that's the case

aarona74
45

Very true john when I purchased the truck they actually had the oxygen sensor unplugged not sure if your able to drive like that or not on the fuel injected engines I'm all for regular carbureted engines and a Chevy man at heart. On another note drove the truck yesterday with no missing or backfiring just wants to buck when you give it too much gas now I am leaning towards the tps sensor oh this Ford lol

Brandon O'Neal
10

Hello. I have a 1992 chevy k1500. I had to take it down to the block and the heads because it was spewing out steam. Ended up being the intake manifold gasket. Anyways I decided to go ahead and replace allot of the stuff because its an older truck. Rebuilt the throttle body ( changed out the gaskets and cleaned it) new water pump, distributor, and etc. Anyways we finally got it in time by pointing the distributor towards the back of the manifold. But me nor my brother in-law have really never worked on a 350 engine and uncooked the wires and vacuum hoses and not sure if there all in the right place. Pretty much put it where it fit. Well anyways the problem I am having now is that when I drove it the engine is revving up high and there is no power. Just kinda scooting. When cleaning the diaphragm in the throttle body the spring piped out. But was put back in. Not sure if that could be causing the issue. Sorry for rambling I just wanted you all to understand what all I've done. Anyone have any answers it would be much appreciated

1 out of 1 people think this is helpful.
John Saffrahn
17,585

You get ask the rockers tightened properly?

aarona74
45

Hi I have a issue with my truck bucking while driving runs great at idle with no hesitation but after putting in gear wants to hesitate and buck usually in the lower gears only slightly at 40mph thru 70 mph and gas mileage isn't the greatest. Runs the best if you gun it through the lower gears wondering if I have a bad tps (throttle positioning sensor or maybe need to install new tranny filter and fluid) Thanks

pnutbttr
0

Ive got a 88 c1500 with a 305. Changed: fuel pump, fuel tank, fuel lines, O2 sensor,distributor, cap and rotor, knock sensor, head gaskets, TPS, MAP, fuel pressure regulator, fuel injectors, and ignition coil. Its hard to start cold, idles rough, lack of power, barely holds 30mph, it acts like it is going to stall when creeping through parking lots. I have also checked the comp board for shorts and burns: nothing there. It keeps spitting out code 44. Please help.

epalacios
25

Hi John! I'm hoping to get your sound advice and recommendations regarding my issue. I have a '94 Chevy C3500 with the 7.4L motor. It was running fine until, one day, I stomped on it and noticed that it hiccuped. When I got home, I changed the plugs, wires, cap and rotor. When I tried to start it up after these changes, it wouldn't immediately start. When it does start (it tries to turn over a few times), the idle jumps to over 1,000RPM and then it dies out. Also, I noticed that the fuel pump is louder than it's ever been. Please help me. Thank you.

chazzychaise
0

Ok I have a 90 gmc k1500 350 5.7.. wasent paying attention while driving and hit a flooded road and truck instantly stalled... couldent get it to start so pull it back to my grauge and found out I wasent getting fuel threw the injectors so I rebuilt the tbi and still wasent getting fuel so I took off my fuel filter and blew it out and then I was getting fuel to my injectors so I started it and ran like crap and my buddy said it sounds like my fuel pump so I was pretty pissed cause the filter and pump were 2 months old but I replaced them and it dident change. . It runs like its surging . .. its a head ack.. now ok I put all new sensors on the top of the motor because I kept throwing the map sensor tps sensor error on computer being hooked up ?? And yea but changed out everything like all the sensors and computer and got it to start and idle but I have to unplug the map sensors or wont idle at all.. so at that it idles like crap and I was messing around .. ohh and no vacuum leaks or cracks in the PVC pipes.. but I took off my egr valve idles great can plug in the map sensor and it idles great but cant start it I know I cant drive it like that but yea and so I pulled my wire harness and found out I have to burnt wires from the exhaust pipe going to the speed sensor so would that do anything?

Camruncarr
10

I have a 98 5.0 chevy silverado 1500. I just bought it a lil while ago and when i got it the check engine light wasn't on it ran pretty good. I fixed a leaking exhaust gasket after the cat before it goes into the muffler. Before that i had the pipe where the gasket divides the two pipes and cranked it up and it idled up and down a couple times and then died and threw on the engine light. I cranked it 3 more times after that and it went away and idled fine. That same weekend i went to crank it and the battery lost connection (the SOB left me a ghetto rigged boat/marine battery). So i unconnected it all brushed it with a wire brush then sprayed it down heavily with WD-40 and it cranked up good. Same thing happened a couple weeks ago (idling part) and the exhaust had been put together for a couple weeks but there is still a slight leak. It threw a code P1351 I think (ignition control module) is what it said. I got a friend to clear it, it hasn't thrown the light since but i looked online and i couldn't find a solution. Now heres the real problem: a couple days ago i ran the tank all the way from full to E and the next day it idled low at startup, but it did crank and not stall. I took it to the gas station filled it up and then the battery had somehow lost connection again and when i went to crank it it didn't for 2 trys then turned over the 3rd but stalled then the 4th try i put my foot on the gas and it cranked and i got home. I was wondering how I can check what it is (I'm thinking fuel pump or filter) (Im not a machanic but ill know what your talking about if you explain it) and for the code it threw I have no idea where to start, i was gona see if you knew anything or have heard anything about it. Also i did turn the throttle stop so it would idle a little higher (it helped a lil) and someone said to try some fuel system cleaner so i put that in but it didn't seem to help much. It will idle fine after it gets into gear but at first crank (cold or warm) it starts but I have to keep my foot on the gas then put it into gear. I know you must be getting fed up with all these breaking down trucks by now but id love to hear something from someone who really knows what their talking about!

1 out of 1 people think this is helpful.
MMRacing
0

Hi I have a 99 Yukon 5.7 Vortec engine that is dying out after driving it for about an hour and a half. It just shuts off. We restart it and it'll drive for another two minutes and the cycle continues. We replaced the fuel cap, changed out the relays, replaced head gaskets, rebuilt the whole engine but the problem continues. Any further advice?

John Saffrahn
17,585

You check fuel pump, fuel filter? Other than that it's an electrical problem that won't be fun to chase down.

MMRacing
0

Replacing the fuel filter today. Fuel pump was replaced 2 years ago.

MMRacing
0

If it ends up being an electrical problem what's the best place to start looking?

John Saffrahn
17,585

Could literally be anywhere, with the key off check the resistance of the fuel pump, heat increases resistance causing electronics to fail until cool. Once it's acting up check the resistance again, you should check from the relay to a good ground like the battery, make sure you're in the pump lug and not one if the other three spots. Seems like a fuel issue due to the fact that it still starts back up even just momentarily. Usually a bad sensor or ecm will take significantly longer to cool before you can get it to start again at all. Since the pump sits in cold fuel it tends to cool a but quicker, the wires and plug are in a much cooler place also showing them to begin cooling quicker. If it passes the resistance test then check fuel pressure when it starts acting up, you can do those in either order or even at the same time, checking resistance will be easier than the pressure test and less messy. Post what you come up with, do NOT try spreading anything into the intake like starting or carburetor fluid to try starting it. I'm not responsible for any damage and if you have any questions just ask, I'll check my emails after work. You posting here sends me an email.

MMRacing
0

Can you explain the resistance and how I would check it?

John Saffrahn
17,585

Working with the fuel pump relay. Four leg relays are reversible, can't screw them up when installing, looking at the relay you should see it's marked with numbers, 87 and 30 are your only concern. They will be across from each other. Find the slot they go into, one side will have battery voltage, the opposite corner runs straight to the fuel pump and then to ground. Pull the relay, find the power slot, test the other slot for resistance. If the pump is overheating due to a bad brush then it will have a higher resistance causing less power to be fed to the pump so it won't run as fast causing you to loose fuel pressure, same exact thing goes for bad wire or connector, electrical diagnosis is a whole different thing. A shop would connect a fuel pressure gauge and check it that way, I'm giving you the resistance test as an alternative that won't be as messy. If you decide to hook up a pressure gauge, before you hook it up pull your fuel pump relay and start the engine. When it dies that means there is very little pressure on the fuel rail making servicing, like hooking up a gauge, less likely to spray fuel on your hands and engine. I'm going to bed, I'll be back in about 15 hours after work.

MMRacing
0

Alright I'll try it tomorrow. Thanks a lot I really appreciate it John!

MMRacing
0

Ok I ended up doing a couple things changed the fuel filter and went through all the wiring from front to back. The ground was burnt and there were a few pinched wires by the fuel tank. It's been running good so far got some extra power now. Hopefully we got the problem.

John Saffrahn
17,585

Sweet

MMRacing
0

Doesn't look like our problem was solved. Once we attempted to go to a race loaded up our trailer and bikes we didn't get halfway before dying out. Now the gas is coming up where you fill it up, which is a new problem. Also when pushing the hazard light switch it triggers the electrical system. One thing we noticed is if we keep it under 40 mph it won't die out.

John Saffrahn
17,585

Hazards trigger what electrical system? You ever do a fuel pressure test? Could be fuel pressure isn't high enough to meet the demands of a higher engine speed, I have seen fuel pumps, alternators, and starters test bad right out of the box. How dirty was the fuel filter? Filter that is pretty clogged can destroy a pump pretty quick,if you still have the old filter place a rag over the filter inlet and blow, a new one will have almost no resistance.

MMRacing
0

The filter was hardly dirty.

John Saffrahn
17,585

I would still do a fuel volume test, fuel pump may create good pressure but if it doesn't pump enough volume it will start dropping pressure at a higher rpm.

mkvealsh
15

OK guys, I have a 1996 GMC Sierra SLE Z71 5.7L, it starts ok cold, when it warms up it stalled immediately unless you keep the gas petal partly depressed, after start it idles rough, seems to surge and misfire almost buck while driving at any rpm, more pronounced when in overdrive at around 1200-1500 rpm under load, I have replaced the crank sensor, camshaft sensor, mass airflow sensor, TPS, EGR Valve, coil, cap, rotor, wires, I have double checked to make sure wiring is correct. I also replaced the fuel filter. Any help would be appreciated

1 out of 1 people think this is helpful.
John Saffrahn
17,585

Sounds like you're stuck in open loop, you get the codes pulled? O2 sensor and engine coolant sensor can both cause this.

jamesgitt
0

Everyone on here has a truck, mines not a truck but i am having trounles with my car. Im hoping maybe someone can help me. You guys seem to know what our talking about. I have a 94 civic with a 98 engine. It hesitates to start unless i am pushing on the gas. Also, it was start kicking back and spuddering around 25-3000 rpms forcing me to shift. It will do that through all gears. Occasionally when it warms up it will run like a champ but not always. Also it seems like my rpm gauge isnt working correctly, it will jum around, hesitate, and act weird. My car also will have different idles as well. Somedays it will idle around 2k others around 1k and everywhere in between. And its not just on different days. Ill turn my car off and start it a few hours later and it will idle at a different rpm. It has tendencies to stall out every now and then as well. Ive done a tune up with new plugs, wires, caps and rotor. Ive put in a new fuel pump and filter as well. Im not sure what to look at next. Please help.

mkvealsh
15

Well, I had the codes pulled and got Vane air flow meter, and cam sensor, both have been replaced as well as the coolant temp sensor, same problem runs rough when warm, occasional bucks and misfires while driving, after it warms up you have to crack the throttle to start it or it will stall right away, also the left bank spark plugs are sooted up, only cyl #2468, fuel pressure key on engine off 52psi, running 48- 50psi. I am getting frustrated with it.

Mark Gardner
10

Hey there, I have a 94' Chevy G20 van with 67k miles that stalls when I put it in drive. It started the same time the heater control valve was leaking fluid but not sure it thats causing the idle problem. I had trouble codes 54, so replaced the fuel relay sensor, was getting 35 and replaced the IAC, then was still getting it for a while with the new IAC, and was getting 34 so replaced the map sensor, but now I'm just getting 34 again with the new map sensor. The IAC makes a loud hissing noise when the throttle is opened sometimes. The spark plugs, rotor, distributer cap, and fuel filter were also all changed. You think it could be a bad ECM, or bad ground, fuel pressure regulator, or maybe bad ac compressor taking too much voltage away? Thanks for your help.

1 out of 1 people think this is helpful.
italianrob
10

Did you check all your vacuum lines

Thomas Hilderbrand
0

Hey John you seem to know ur stuff soon I have a question also. I have a 98' suburban k1500 it has the 5.7 in it. Over the last few days it has had a really rough idle so much it shakes the trk and it sputters when I'm driving it, if I try to get on the gas it hesitates and then slowly picks up whole sputtering. It doesn't do it all the time but seems to be getting worse daily. I've checked the plugs, wires and vacuum lines and couldn't find anything wrong no cracks or loose lines and the plugs and wires were still in good shape. It almost seems to be starving for fuel butiI'm not 100%. What would u recommend checking?

Thomas Hilderbrand
0

Sorry for the misspelled words my spell check attacked me. Any ways I also have no codes or coming up/ no ck engine light even coming on

John Saffrahn
17,585

What is the engine temp when doing this? Check fuel pressure.

Thomas Hilderbrand
0

It does the same cold or hot, do you know if AutoZone, orielly etc. Rent the fuel pressure testing tool

John Saffrahn
17,585

Yes I believe you will need the adapter that sits in place of your fuel pump, just a piece of line with a Schrader valve on it.

Thomas Hilderbrand
0

Thats usually by the fire wall under the hood correct?

Mark Gardner
10

Ya the vaccuum lines seem fine from the spraying the lines with starter fluid test, I'm gonna adjust the timing tomorrow and if that doesn't work I'll check the fuel pressure as well with an O'reilly rental.

italianrob
10

Sounds like you having the same problem I had. After taking to John I bought the fuel pressure tester and when I removed the fuel filter to use that line to test pressure I realized the filter was plugged severely. I had the same sputtering stomp on gas symptoms ..7 dollar part who would of thought I didn't change it for 25 years...

Mark Gardner
10

Oh that's cool you found it, I had my fuel filter replaced with the tune up I had and didn't fix the problem unfortunately but I'll keep plugging away at it and see what happens.

John Saffrahn
17,585

No Thomas, unfortunately these didn't come with a factory Schrader. Mark fuel filter is inside the frame, drivers side, right around the back of the drivers door.

John Saffrahn
17,585

Be very careful when using starting fluid to check for vacuum leaks. Back in high school I was at a shop and a guy brought a car in that was shaking all the time, running horrible, you could hear the electrical arc from the misfire. I brought it in and as the know nothing teen I told one of the older techs it sounds like a misfire, I can hear the spark jumping. He proceeded to push me out of the way and say it's a vacuum leak I see this all the time, the noise is knocking from running lean. Thought whatever and walked away, I could hear that arc clear as day and a vacuum leak small enough to allow the car to idle rough will have 0 effect on the engine once the throttle is depressed about 1/4. He grabs a can of carb cleaner and proceeded to check for a vacuum leak, luckily he found the burnt spark plug wire pretty quickly so the engine wasn't soaked in flammable carb cleaner when it went up in flames. Fire was small and nothing was damaged but the lesson to learn is that even if there is a vacuum leak something as small as a loose wire can ignite carb cleaner. Use propane or some form of flammable gas not liquid, have a fan at the front of the car, turn on the gas, cup your hand behind the line and trace one line at a time. Remove the gas source from under the hood after each pass for about ten seconds, everything should dissipate and go to the next line. Little propane bottles are good for this. Tape the air holes at the base of the torch so it's straight propane coming out of the end. If it does manage to ignite the propane bottle can be removed quickly and the fire won't last more than a split second, it will be more like a puff of fire.

Thomas Hilderbrand
0

Hey John on my 5.7 I was wrong I thought it seemed pretty even from when it was happening being cold or hot. I changed the fuel filter yesterday to see if that would help before doing the fuel pressure testing(AutoZone wants 150 deposit for the rental and can't afford that right now lol) and ways it seemed to run better yesterday and the sputtering only happened a few times but it was hot. This morning was colder than it has been and it ran horrible taking my kids to school it was sputtering so hard trying to drive the trk started shaking and had no power even trying to get on it a little harder didn't help. Do you still think fuel pressure problem or maybe something else? I dont think its connected but on cold mornings my tranny acts up and bucks when coming to a stop it doesn't want to download shift and taking off shifting from 1-2 gear it jumps could that be causing any of this or what would that be? I appreciate all your help.

John Saffrahn
17,585

Does it take a long time to shift and then it's solid, gas mileage is crap, and the sputtering and shifting happen together? No check engine light?

1 out of 1 people think this is helpful.
aarona74
45

Hi John mine has almost all the symptoms of the other guys but shifts early,bad gas mileage replaced vacuum lines and does a lil better but still runs kinda crappy especially from 0 mph to about 35 mph then I can just keep pressure on the gas pedal and runs really good and runs good at 70-75 mph almost perfect. Thanks for any help John. Aaron 1992 Ford F-150 4x4 5.0 efi

Thomas Hilderbrand
0

Gas mileage is worse than normal, the shifting happens right in the normal range it justice jumps when it does shift especially the down shifting at a stop light etc. The sputtering happens even when the tranny is acting good the tranny only does this cold once its warm it doesn't happen anymore at all, and ck engine lights on. There used to beone that would come on occasionally but then go away but atthe time it ran great no mech issues then but no light now that it does all this

mom091213
40

Havein the same problem on a 89 Oldsmobile cutlass ceira.. changed the fuel pump twice first time didnt work so we had to replace it the sec time ran but cuts off under 20mph. Also has new fuel filter

Thomas Hilderbrand
0

Hey John I never learned what the smell of running rich smelled like but I did notice this morning while it my trk was running horribly a smell that was like exhaust and fuel mix pretty strong I never really paid attention tobefore. Is that running rich? If so that would pprobably mean a vacuum line I missed leaking correct? Thank u for any help

John Saffrahn
17,585

Rich is the sam smell you get when you first start a cold engine. No vacuum line would be lean. Sounds like it could be the mass air flow buti wouldn't throw parts at it. Try getting some mass air flow cleaner pull it out and spray it down.

Thomas Hilderbrand
0

Ok thank u I'll try to clean that, it could be one of the O2 sensors to correct? I'm gonna try to clean the maf first though thats cheaper lol

John Saffrahn
17,585

O2 sensor usually throws a code and won't cause hard shifting.

DirtyDave0528
5

i have no check engine light like you said a few comments ago and all the symptoms you mentioned along with it. what would make this happen? FYI my 89 sierra has 350 tbi with heddman hedders w/o 02 bung. No 02 sensor at all. I can spin the tires like no other when power breaking but on the road it dies when i give it too much pedal...

John Saffrahn
17,585

Your check engine light come on when the key is on and engine isn't running?

Thomas Hilderbrand
0

Hey John I cleaned my maf sensor and changed my air filter cause it was dirty to. My trk is running better but still has some sputtering, it does have more power and I can hear a difference in the way its running but still has some sputter what shouldiI look at now?

fireman123ca
0

Hey guys maybe some one can help me here I have a 1999 chev suburban 1500 the truck will idle nice but when you step on it about 4000 rpm the engine starts to pop and cough won't die but run real rough at idle it's OK if you step on the throttle slowly you can get past 4000 had it on the diagnostics could find what was wrong so the guy said try replacing the cap and rotor well they were pitted pretty good so changed it with no change still runs rough. Could it be my fuel pump I have 52 psi on the purl pump now when running ? Help lol

Thomas Hilderbrand
0

Hey John so I cleaned the maf sensorand changed my air filter for good measure it was filthy my truck had completely stopped the sputtering and loss of power, until this morning it was our first morning where it was pretty cold out. The truck went right back to idling rough but seems only when in gear, and the sputtering while driving. Any ideas on what to ck next? Thank u for your time and help.

John Saffrahn
17,585

Fireman sounds like air filter or clogged exhaust. Thomas You cleaned the maf in the intake tube or iac in the throttle body? Carb cleaner the throttle plate, idle air control if you haven't, and if you can easily get the egr off clean it too. No codes?

Thomas Hilderbrand
0

No codes at all, I cleaned the maf sensor in the intake tube, I will clean the iac and ck on the egr also thx

John Saffrahn
17,585

If you try pulling the egr and it doesn't come easy just leave it for now.

aarona74
45

Hi again John I had talked to you in the past about my Ford nightmare lol and thanks for all your great advice. I recently unplugged my map sensor and seems to idle regular and drive pretty good. I am curious if this could have any side effects if I just leave it unplugged although it does die once in a while? I was curious if there is a way to set fuel preassure mine runs really really rich can smell it from the exhaust. I was also curious how hard it would be just to convert to carburated and just take all the sensors and crap off for the efi and just run simple wires and vacuum lines. Or would it be cheaper to just buy a Chevy since I am getting about 5miles to the gallon now with no performance. Thanks again, Aaron

John Saffrahn
17,585

Replace your map sensor, the freightliner semi trucks I work on get 9.

aarona74
45

I will have to try that thanks john I am getting about 40 to 45 miles on a quarter of a tank of gas. Is this a common trait of the map sensor going out by chance causing poor gas mileage. Thanks

John Saffrahn
17,585

Any bad sensor decreases gas mileage, the fact that you unplugged it and it got better usually means it's bad but within specs,

Thomas Klar
0

John, I have a 1990 GMC 5.7 liter suburban with 289,xxx original miles on engine and trans. had it for about 11 years now, I keep it serviced and parts replaced as needed, 2 radiators 2 alternators starter, water pump and so on... It started running rough at idle 1-2 years ago, it starts up and runs ALMOST PERFECT when cold in the mornings, however the problem is most pronounced when I start it back up when it's still warm, (has been run in last 3-4 hrs.) It fires right up smooth, but when I barly push the gas it starts like going choppy. If I let off the gas it'll [engine] slow way below idle almost die and then catch back up to normal idle ( 1-3 times a week it will stall in this situation). In stop and go traffic or parking lots is what I hate. If I step on it a little she will go good, the problem is starting to become more pronounced as the miles keep clocking. Fuel pump has about 25- 30,000 on it, new fuel filter a year ago, the fuel press is within tolerance, low mileage plugs, and dist. Also new o2 sensor 1.5 years ago. I replaced the PVC valve a month ago with no help to the situation. However I noticed that the vacume port that it goes to has NO vacume. Can a clogged throttle body vacume port cause this problem. Ask me any question I probly know the answer cuz I've had this truck for so Long. Anything I've tryed in the past to fix this only helped a little but never "cured" the problem. Thanks, Thomas

John Saffrahn
17,585

Pcv port shouldn't have idle vacuum on it, should have very little vacuum at a higher rpm. Fuel pressure stays good after shutting the truck off? What kind of engine tennis are we talking about on restart? Only runs rough at around that 3 hour mark on the restart? Have you gotten a good throttle body and fuel system cleaning recently? I have a lot of maybe things but nothing I could set you straight onto. Have you hooked up a vacuum gauge when it's doing this? Does giving it more gas help if make it worse? I would start by pulling the spark plugs at the the hour mark. If they look good then put them back in start it, make it run bad for about 5 seconds and pull them again.

Thomas Klar
0

Fuel press is good, have not done any vacume gauge test, however I have cleaned the throttle body THOUROUGHLY several times with carb cleaner in the arosal can and a few recent in tank treatments also, and it runs rough and a little choppy at low rpm and low speed any time I start it warm to hot, it pretty much runs choppy as stated above after it warms up and goes to closed-open loop, I can't remember which is which[open- closed loop] I know the sensors take over engine management after warm up. What did you mean by saying "What kind of engine tennis are we talking about on restart?" What do you mean by "tennis"? My engine never backfires at all ever, timing it perfect, I've replaced almost all vacume lines over last several years, any more suggestions? I guess later this month I'll try running my computer on it and see if good info is being fed to computer. It's just annoying cuz I take care of my car and don't run like it should sometimes. My dad doesn't do a dang thing and his runs like a champ....

Thomas Klar
0

And when It does it's thing I just give it some gas and it goes fine.

John Saffrahn
17,585

Hahaha damn phone, temps not tennis.... you give it gas when it starts running choppy and it will run fine after giving it gas or run fine with gas and then run choppy again after the pedal is released? It runs fine once it goes into closed loop after warming up? You try pulling the plugs? See if they are wet?

Thomas Klar
0

Any engine temp 100-190 will run choppy right above idle. (Pushing gas slightly for slow acceleration) Like I said unless it's cold in the morning it runs bad a little above idle, ESPECIALLY right after warm restart but also normal op temps. and yes I give it gas or I let off when it starts chopping or bucking. Eather way helps. The plugs look pretty good considering the mileage on engine, there is one cylender that let's a little oil in but not much, it's only a quart or 2 between changes but only half that it from burning, I need to replace the pan gasket just never get around to it, anyways the plugs have never really been wet from too much fuel if that's wat your asking. Lastly, I was reading another post and someone mentioned the car not "breathing" good, my catalytic converter probly needs to be bored through(something I've done on several cars) I would take it off but I need to make it look like it's there for inspection. Could that help at all? Also imma check for any codes tonight I just thought I should check, engine light came on one time a few months ago for a few min,

John Saffrahn
17,585

Cat might be getting a little clogged, I doubt though. Clogged cat usually restricts higher rpm, doesn't usually mess with the idle.you checked the plugs right after it was running bad? Gap looked good on all the plugs? Just because they are newer doesn't mean one isn't worn pretty bad, if you have one not firing it will cause a bad vibration in the engine and make it buck. Usually once the plug starts firing again it won't show an issue until it gets fouled again. Could be getting fouled at idle or when it's getting started. Replaced a set of plugs today on the brother in-laws car because it was very hard starting and would shake until you hit the gas and got it to clear up. Gap on the plugs were a bit off from the metal wearing away which is normal and one was carbon fouled.

Thomas Klar
0

I'll pull the plugs and see what's going on there, but when I replaced them a year ago it did not help or make the problem worse, I will have to get back in a while on that one when I got time to get elbow deep in my ride, I just got through replacing front ball joints last week, upper and lower, u know how that can be after almost 300K

John Saffrahn
17,585

It's more whether or not the plugs are going to be fouled rather than worn.

1 out of 1 people think this is helpful.
tim4548
0

Have a 94 gmc box truck 7.4L. Runs great in park but wants to die in drive. Changed plugs and wires, now i have a code for IAC would that cause it to die in gear?

chrysler4201
0

I have a problem with my 90 gm k1500

chrysler4201
0

Code 15 33 34 42 44

chrysler4201
0

when started initially it starts then dies immediately when I unplug the MAP sensor from the vacuum line it seems to run just fine but when I plug it back in it stalls out when it gets up to operating temperature it seems to idle okay but still rough when I unplugged the MAP sensor from the actual prongs it also seems to run okay I put a new one in it does all the same symptoms keeps telling me I have a signal to low and signal too high I put a test light up to each prong I have good power and good ground but unsure of signal my coolant temp sensor will always read -36 though the test gauge reads proper temperature I have replaced the temp sensor with three new ones and all the same symptoms happening I have a feeling that the temp sensor is causing most of the issue with it not being able to run it a proper temperature it's telling the system to run lean any ideas on how to fix it

chrysler4201
0

Dash guage ** when's she's warm she seems to be ok ....kinda it idles up and down

cploysy
0

Hey guys. I have the same exact problem. But I have a 91 acura integra with 150k on it. The car runs fine when it's cold. But as soon it's warmed up. The idling sputters when I half or fully throttle it and when I get over 3000rpms, it OK sometime. Should I try the brake/carb cleaner first before checking or changing fuel pump? Some advice or answers would be very much appreciated. Thanks in advance

cploysy
0

And I also meant checking All the other stuff like hoses and what not

WarIII
10

Hi John, I have a 1992 chevy k1500 5.7L just recently it started bogging down when I try to accelerate. It gives me the code 44 for lean exhaust. It runs ok as long as I baby the throttle up to 35 mph after that it won't gain no speed and acts as if it's bogging out. There is no power at all and when the gas pedal is pressed all the way it's like it tries to die. Would a bad O2 sensor cause this?

1 out of 1 people think this is helpful.
Richmond Bullock
0

Hello everyone got a ? I have a 1996 chevy 4x4 ive pluged up the code reader and it keeps telling me mass air flow sensor ive replaced that and the secondary air flow sensor. But the truck still when you put it in gear chokes out and then you have to recrank it. when the truck finally gets going it runs like a top with no problems just have a rough time when you put it into gear. thank you for your help and advice

kingjames6
0

I have a 95 mustang gt 5.0 v8 while I was driving the car just shut down and I got my friend to come look at it cause he went to school for mechanic work and he said it's either a bad fuel pump or fuel filter is clogged, when I turn the key over to I can hear the (buzz) sound so I'm getting fuel and my friend checked if I had a blue spark and I did, and I don't have tools on a ranch and screw driver and I already replaced my fuel filter still won't start. Pls help or call me and walk it over with me pls 4793407122.

Jr. Doran
0

someone help please i have a 1988 chevy c3500 with the 7.4 454 it will start and idle good fo a min and if you get in it and go rite away it is driveablr but with in a min it starts acting like its runing out of fuel and popping through the tbi heres what ive done so far fuel pump,map sensor, ets, distributor, coil, fuel filter, i forgot to mention whe it acts stupid if you switch it off then start it rite back it is good for a min again then starts acting up does this every time

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