stalling 5.7 tbi

[BamBam]

:neutral: Ok, guys...I joined this forum just for this problem. Recently bought a used 92 Sub with 5.7 TBI. It's my first GMC ever . It ran ok, but was in need of a tune-up. It would stall while sitting at idle in park or when in gear at a stop sign. It fires right back up very easily. I replaced the plugs, wires, cap, rotor, and air filter. Ran better, but still stalled. Did some research and replaced the Idle Air Control Valve...still stalls. Replaced the TPS next...same prob. Runs great as long as you're on the gas. I can take it down the highway with no problem at all. But if I sit and let it idle for more than about 10 seconds it dies. So I end up double-footing it to keep the rpm's at about 800 so it doesn't stall. Any insight? Thanks in advance!

[unplugged]

:sign0016:Intake manifold gasket leaks are common. Test for a vacuum leak.

[BamBam]

The adventure continues! In all, I have replaced the TPS, IAC, MAP sensor, EGR valve, all vacuum lines, fuel filter, plugs, wires, cap, rotor. I took the injectors off and cleaned the assembly, however you can't really clean the injectors, can you? I have yet to test for vacuum leak, but it did run better after I replaced the vacuum lines. Just thought maybe someone had some more insight now that I have replaced more parts.

[Chris Miller]

It's your intake manifold gasket. My mother had the exact same problem in her '94 suburban. The passenger side gasket was leaking at the #2 intake port.

[justcuz]

Does it lope or just stall. Put it in park and rev it up, look and see if the EGR valve is opening. This is the problem I am having. The EGR valve is opening with the vehicle in Park or neutral and is almost stalling when you stop and idles very lopey.

I have swapped out the EGR Valve, the EGR solenoid, the MAP sensor, the Temp sensor and adjusted the neutral safety switch. I swapped these out with known good parts from my 93 Suburban. Nothing worked.

It throws a code 32 (EGR) and when I plug the vacuum line or unplug the EGR solenoid it runs fine, minus the EGR function of course.

I looked at a wiring diagram and see that the EGR solenoid shares a curcuit with the O2 sensor. I wonder if the O2 sensor is bad?

[BamBam]

Ok, in addition to all the work done previously, I have replaced the intake manifold gasket...same problem still. The only other things I can think of are fuel pump (which I was told by previous owner was replaced), and possibly the coil???

[Project Reaper]

i dont know if you can get this tested but if your running rich as hell because of a bad O2 sensor it will lope and stall at idle. it might even throw, i would check those. if it was just a bad fuel pump then you could just check the fuel PSI lvl and that would tell you right there.

[BamBam]

Well I found another vacuum solenoid for the egr valve that I overlooked while replacing stuff so I'll replace that as well as the O2 sensor and the coolant temp sensor. That will be all of the solenoids and sensors on that engine. Other than that I have no idea and will probably take it to a GM Garage and let them diagnose it.

[k.daddy1]

Ok, in addition to all the work done previously, I have replaced the intake manifold gasket...same problem still. The only other things I can think of are fuel pump (which I was told by previous owner was replaced), and possibly the coil???

Replace your fuel pressure regulator. Your not keeping a constant pressure to the fuel system.

[BamBam]

Ok, I replaced the EGR Vacuum Solenoid and coolant temp sensor. No change. Everyone seems to have a different idea as to what it might be. In all I have changed:

1.) plugs
2.) wires
3.) cap & rotor
4.) fuel filter
5.) EGR valve
6.) EGR solenoid
7.) Idle Air Controller
8.) Throttle Position Sensor
9.) Map Sensor
10.) All vacuum lines
11.) Coolant Temp Sensor
12.) Intake Manifold Gasket

It throws no diagnostic codes other than 12, runs great down the highway, never fails to start on the coldest of days. When it's stone cold, it will idle fine for about 15 minutes till it warms up and then stalls. I'm at my wit's end and it's quickly turning into a money pit.

[Viper]

if it idles fine until it warms up you might have and O2 issue, but seeing as you've thrown parts at it hoping for success I would recommend taking it to a GM dealership, or another garage to have them fix it,

[Viper]

there is something the computer is not liking once it runs in closed loop mode, and its either dumping toom much fuel or not enough.

also just because you replaced the sensor doesn't mean the circuit itself is working, it could still be a simple wiring issue ie bad grounds, or short circuit.

[BamBam]

Thanks for your input. I think I will take to a service center and see what they come up with. It seems to me if a circuit wasn't working the service engine light would come on and a code would be generated. I probably would be money and time ahead if I would have taken it in sooner, but I rarely have this much trouble fixin' junk.

[thattallguy32]

could you perhaps post an update once you find out from the shop what they find the problem to be, as i am having these exact problems and cannot figure it out for the life of me.

[BamBam]

As soon as I get it fixed I will post the info! Thanks for all your input.

[thattallguy32]

just got mine fixed and thought i would post a quick update... incase anyone else was following this with the same problem.

Turns out my Diaphgram was actually leaking gas, the rubber gasket was cracked to ****. So the engine wouldn't get the full amount of gas that was being pumped so the computer kept over and under correcting for it. got a new diaphgram from a wrecker, replaced all the gaskets with a rebuild kit and now it works like a charm!

[94bluebeast]

I have a 94 burb. bought it 4 years ago with about 237,XXX miles on it for about $2,700 and both intake manifold gaskets leaked pretty bad. It now has a little over 365,XXX miles on it KBB said its still worth about 4 grand, lollololololololololollolololo.. and I have still not fixed the gaskets. It never caused a problem( except I had to change oil every 2,200 miles).Question, do you notice any oil in you radiator or overflow tank,,,,and is there and water in your oil, check dip stick for a light brown foam.
In fact I only just started to strip off the manifold to fix it to kill time while I replace my entire braking system... Well it seems that you spent near a grand or more and still not fixed... Try this tho most of us guys love fixing our own truck. Go to a pepboys or any other locally known garage, pay for the diagnostic then go buy the part you need and fix... 60-80 bucks is not a bad investment as long as it points you in the right direction... Good luck and best wishes... Ray Z...

[BamBam]

just got mine fixed and thought i would post a quick update... incase anyone else was following this with the same problem.

Turns out my Diaphgram was actually leaking gas, the rubber gasket was cracked to ****. So the engine wouldn't get the full amount of gas that was being pumped so the computer kept over and under correcting for it. got a new diaphgram from a wrecker, replaced all the gaskets with a rebuild kit and now it works like a charm!


What diaphragm sre you referring to? Fuel pump?

[BamBam]

Okay, replaced diaphragm for fuel pressure regulator and TBI gaskets...still same problem. Truck does not throw any codes, I have been to Autozone and Advance Auto for scanning. I guess all thats left is the fuel pump and injectors.

[justcuz]

I remember reading some where you can check your TBI injector spray with a timing light. However since it is just doing it at idle you should be able to see it with the air cleaner off. It should be just a little spray at idle, no drips from the injector nozzles. If the injector nozzles are dripping fuel it is too rich and the IAC will cycle to compensate and cause your problem.

Do a compression check also, if you have a weak valve spring or a burnt or non-sealing valve it will smooth out at speed but be rough at idle. Sometimes you can adjust the valves and fix it. Worse case scenario here is a cam lobe going away.

Lastly does it use oil? If oil is leaking down the guides and causing an over rich condition when you come to a stop. You can tell if your guides are leaking a little by a puff of oil, after a hot restart. Normal cold starts should be OK but a hot restart will burn off oil that has run down the guides into the cylinders. If that is the case you may be getting a temporary overrich condition when you suddenly release the throttle and the vacuum created pulls oil down the guides into the cylinders, resulting in a uneven idle untill the oil burns off.
This usually happens when exiting the freeway or after a long stretch on a highway or road.

[thattallguy32]

What diaphragm sre you referring to? Fuel pump?

umm the one on the throttle body itself, its like a little pod thing, on the back part of it. i could post a picture if you need me to?

[92WT]

Next time it does it when its warmed up unplug the O/2 sensor, thatll piss it off but it should force it to ignore the sensors as if it were cold. Thatll tell you if the problem is the computer reading from the sensors and doing something stupid or if its actually a heat related problem. If its heat related I didn't see a distributor on your replaced list, could just be the ignition module in the distributor overheating but for some reason on mine when it warmed up the magnetic pickup in the distributor would crap out and it would die under a certain rpm.
If its the distributor put it on #1 top dead center compression stroke if possible though I got lazy on mine and just marked where the rotor was pointed and how the distributor itself was indexed, then set the timing. Also note how much the rotor moves and in which direction as you pull it out, makes install easier since the drive teeth are heli cut and the rotor will rotate as you push it in or pull it out.

[BamBam]

Finally figured it out guys! I was going to take ECM off distributor and have it checked. I noticed metal shavings on rotor. I grabbed the dist. shaft and it moved back and forth about 1/8" !!! The bushing was shot. So at idle the shaft wobbled all over,causing the rotor to gouge the cap contacts, and at speed, the centrifugal force on the shaft made it spin true. That's why it ran great on the highway, but poor at idle. Bought a reman. distributor with the ECM for $99 at AutoZone, and this thing runs sweet. It has 257,000 miles on it now, but you could never tell by driving it. I want to thank all who responded to my posts. I really appreciate it. I am amazed at how tight knit a "family" you GMC owners are!:party: