I need help with a 1993 gmc 5.7L tbi.

20

Asked by May 05, 2015 at 11:52 PM about the 1993 GMC Suburban K1500 4WD

Question type: Maintenance & Repair

Ok, so i have a 93 gmc suburban. I just put
a new engine in. It has flat top pistons
running about 9.2 to 1 compression and an
rv cam. The truck itself has about 282000
miles on it. I am having an issue with the
engine wanting to die at about 1000 to
1200 rpm, it never dies out but comes really
close. After that it clears up and runs ok. It
seems to correspond with the egr, because
as soon as the egr closes all the way it
clears up. But if i let off the gas quickly it
will do it again and almost die. But then it
clears it up and its good. I have replaced
the distributor, new cap and rotor, new plug
wires, tps, iac, knock sensor, both injectors,
ecm, egr control valve, the temp sensor for
the ecm (the one right next to the
thermostat).  I am also having a problem
with it stalling when put into gear, reverse
or drive. This is a new problem. It seemed
to start right after i put a muffler on it. I am
losing my mind over this truck. Someone
please help.

24 Answers

98,515

With engine off, use a hand vacuum pump and pull a vacuum on the EGR valve, watch the shaft and make sure it moves all the way open, then quickly release the vacuum, the valve should snap shut quickly, if it does the valve is good, if it is slow in the closing speed the the valve is bad and needs replaced, if the valve checks good all the way then check for a dirty EGR solenoid filter, if it is clogged the vacuum won't release quickly and you get the EGR stumble. As far as the dying at idle, it could be EGR related, pulling on too soon due too a weak internal spring, also did you do a complete reset and relearn of the ECM after all of the repairs? Is the new muffler a low restriction muffler? With an RV cam the lower the exhaust back pressure the better.

20

The egr is slow to close and is also easy to open. Thanks for the help im going to try that today. Will post results. Also i did disconnect the battery to let the ecm reset. Is there more i need to do?

98,515

Okay, that sounds like the valve is bad. After you replace the the valve and reset the ECM then set the park brake or block wheels, start engine then step on the brake put the drive turn on all accessories, ie A/C, heater fan, headlights etc. just let it idle for about a minute, then everything back off and shut it down, then drive it as you normally do, this system is fairly simple in the basic programming so 5 minutes should Bo the trick, and that's it. Hope this helps.

20

Ordered the egr from napa, it will be in tomorrow. After i replace it ill do the reset and relearn of the computer ill post back with if it fixed it or not. Really appreciate the help.

20

Replaced the egr, the egr stumble is gone. Still wants to die out when put in gear but not as bad as before. Thanks for the help. It is appreciated.

1 of 1 people found this helpful.
98,515

Ok great, now try cleaning the the throttle body, even TBI's get dirty, then carefully remove the ISC motor and look at the pintle, you should see a slight wear mark where the pintle seats in the port, make sure that wear mark goes all the way around the pintle, if it don't the shaft is damaged so the ISC will have to be replaced, if it does then it needs to be tested for proper operation, they do make a theater for those but you might try someplace like NAPA they may have an ISC tester just like they do for TFI ignition modules, or if you don' want to go through the whole hassle, just clean the ISC port and replace the ISC motor, just make sure that the new ISC motor pintle it as close or closer to the main body before installing it or you could damage the new motor. After that, set the park brake, step on the foot brake, turn the key on wait about 3 seconds, start the engine and put it into gear, and let the the unit hunt for the proper idle. That should do it. HTH

1 of 1 people found this helpful.
20

Is the isc the same as the idle air control? If so i put a new one in and made it. 1 and 1/8th like the instructions said. But it is still sucking air through the triangle hole. Should it be completely closed off when the vehicle is warmed up.

98,515

No, that is the idle air intake, it goes from there through the ISC pintle and seat and below the throttle plate. And yes the ISC is the idle air control motor.

1 of 1 people found this helpful.
20

So hpw shpuld that be adjusted. Clear closed?

98,515

Run engine to operational temp, shut down, block IAC port, start the engine and let it idle, if it won't reset minimum air rate until it will idle at 650RPM. Shut it down, unplug ISC port, restart engine put in gear, turn on accessories, let idle stabilize, and that should do it.

1 of 1 people found this helpful.
20

I have tried that. It still wants to die.im at the point where fuel is about the only thing That could still be an issue. I am going to change out the fuel pressure regulator tomorrow and see if that works. After that its pretty much time for a grenade. Lol

20

The only thing that seemef to make it run better was taking the iac and backing it out while the engine was running. Letting more air in was what made it run smoother and not die when put in gear. So im thinking the diaphragm in the regulator is bad and its just dumping entirely too much fuel. Tell me if that sounds reasonable. Again. Thank you for the help.

98,515

Usually if too much fuel you would get a code for it. Strange, loosing up the ISC would make it run better, so you are leaning it out, I guess the spring in the regulator could also fail and give you more fuel pressure than needed.

20

Well while i was stopped at a light and it was bogging down (im guessing flooding out). The service engine soon light came on. But i couldnt keep it on long enough to get a code read on it. When i put it in park at the parts store and the idle leveled out, a little, it would go off.

98,515

Did it by chance store it in memory?

20

Not sure.they said they cant run the obd unless the light is on.

98,515

Must be using a Baud rate reader. Go to. www,trouble codes.net/GM It will show how to pull the codes yourself, the code page is towards the bottom after the VIN identification info.

1 of 1 people found this helpful.
20

Ok, so i have done everything. There is nothing left to replace reset redo. Nothing. It still wants to die when it gets hot. Runs like a champ when its cold. Once i get to operating temp. It all goes to shit. The only thing i can thin of is that this problem started after i put the muffler on. Too much restiction? I have no idea. Im at a loss and ready to thrash this damn thing. I have sank a bunch of money chasing the damn problem. To no avail. Im losing my mind. If you ever thought you were a good mechanic work on a gmc. That will bring you back down a couple of notches.

1 of 1 people found this helpful.
98,515

It is possible, too much back pressure, but it should be worse cold when the mixture is richer, they make a kit for exhaust system back pressure testing, fairly straight forward too. I hope you did check the grounds on the engine for the ECM and the ground to the engine from the battery.

1 of 1 people found this helpful.
20

I have taken grounds off and cleaned them and rechecked them.

20

Still no change in the situation. Runs fine when its cold get to operating temp it wants to die at lights and sometimes even in park and at idle.

10

What happen with the truck.i have 93 1500 suburban im rebuilding the tbi.trying to get rid of problem, i thought it was fuel.pump.i think.its mi.throttle position. Sensor

1 of 1 people found this helpful.

Vary helpful ! Thanks to you both , I've been working with a similar issue 93 K1500 5.7, mine however is at start up just 30 sec to a couple of min.while cold, the goes away? Going to try the ECM and will keep updated, I too am chasen with parts that do not resolve the issue.

Here's what happened to my truck (1993 silverado). When I bought it someone had put on an aftermarket exhaust. I fought the same issues; engine ran great when cold, but when it got up to temp it would hesitate stumble and pretty much run like crap at all speeds except wot. the problem: not enough back pressure in the aftermarket exhaust. the o2 sensor was not staying warm enough to work properly so the ecm was dumping fuel into the mixture to compensate for what it thought was a cold engine. That is why the engine ran fine at cold temps but crappy at operating temp. What you can do: 1) new exhaust that maintains the stock back pressure. 2) install a "3 wire" o2 sensor which heats itself and doesn't need the back pressure to maintain temp. You see this problem all over the internet forums misdiagnosed as a egr problem when it is a back pressure problem. hope this helps.

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