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rough idle, stalling, loss of power.

dragonflyoffshore
990

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?

116 Answers

tenspeed
45,645

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.

7 out of 7 people think this is helpful.
John Saffrahn
12,825

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.

6 out of 6 people think this is helpful.
dragonflyoffshore
990

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.

42 out of 42 people think this is helpful.
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dragonflyoffshore
990

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.

43 out of 43 people think this is helpful.
John Saffrahn
12,825

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

3 out of 3 people think this is helpful.
John Saffrahn
12,825

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.

2 out of 2 people think this is helpful.
dragonflyoffshore
990

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

1 out of 1 people think this is helpful.
John Saffrahn
12,825

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

1 out of 1 people think this is helpful.
dragonflyoffshore
990

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.

1 out of 1 people think this is helpful.
John Saffrahn
12,825

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?

3 out of 3 people think this is helpful.
dragonflyoffshore
990

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

1 out of 1 people think this is helpful.
dragonflyoffshore
990

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.

3 out of 3 people think this is helpful.
dragonflyoffshore
990

The new one still gives me the lean code 44.

2 out of 2 people think this is helpful.
John Saffrahn
12,825

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.

1 out of 1 people think this is helpful.
dragonflyoffshore
990

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.

dragonflyoffshore
990

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.

John Saffrahn
12,825

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.

dragonflyoffshore
990

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.

1 out of 1 people think this is helpful.
dragonflyoffshore
990

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

5 out of 5 people think this is helpful.
John Saffrahn
12,825

Awesome glad you got her fixed.

1 out of 1 people think this is helpful.
georgiacop1986
5

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

John Saffrahn
12,825

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.

2 out of 2 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
10

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

1 out of 1 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
10

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.

1 out of 1 people think this is helpful.
John Saffrahn
12,825

You try replacing the tank pressure sensor yet?

chrisdelia45
35

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?

3 out of 3 people think this is helpful.
Ryan McClung
20

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

1 out of 1 people think this is helpful.
Marcgmc96
95

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?

4 out of 4 people think this is helpful.
John Saffrahn
12,825

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?

1 out of 1 people think this is helpful.
Marcgmc96
95

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
20

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##///!!!!

1 out of 1 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
12,825

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?

Estep76
130

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

10 out of 10 people think this is helpful.
Estep76
130

Be greatly appreciated thanks

1 out of 1 people think this is helpful.
Estep76
130

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.

2 out of 2 people think this is helpful.
John Saffrahn
12,825

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

firemedic44
10

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
30

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
30

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.

2 out of 2 people think this is helpful.
John Saffrahn
12,825

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

John Saffrahn
12,825

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.

Marcgmc96
95

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.

4 out of 4 people think this is helpful.
You think this is helpful.
Marcgmc96
95

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
12,825

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

Marcgmc96
95

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.

firemedic44
10

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.

John Saffrahn
12,825

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.

1 out of 1 people think this is helpful.
John Saffrahn
12,825

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

John Saffrahn
12,825

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.

Marcgmc96
95

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
95

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

John Saffrahn
12,825

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.

Marcgmc96
95

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?

John Saffrahn
12,825

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.

John Saffrahn
12,825

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...

Wildfire Day
40

John need ur advice plz

Wildfire Day
40

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?

4 out of 4 people think this is helpful.
Mgmprofits
0

Testing

Mgmprofits
0

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
10

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..

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

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

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

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
0

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
12,825

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.

John Saffrahn
12,825

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
12,825

Rent a fuel pressure tester from AutoZone.

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
12,825

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

biggamer
20

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?

2 out of 2 people think this is helpful.
John Saffrahn
12,825

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.

biggamer
20

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
12,825

Yup

Vildobottomdiva
25

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
0

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

Vildobottomdiva
25

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
12,825

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

alexamador
5

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 ????

John Saffrahn
12,825

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

Certy
10

Dpfe sensor

1 out of 1 people think this is helpful.
John Saffrahn
12,825

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

alexamador
5

Thanks guys

bassmaster63
0

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

John Saffrahn
12,825

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

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
12,825

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
12,825

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
12,825

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
15

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
12,825

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
15

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
12,825

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
12,825

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

aarona74
15

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
15

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
12,825

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
15

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

aarona74
15

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

John Saffrahn
12,825

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
12,825

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
15

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
15

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
12,825

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
15

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
12,825

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
15

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

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