1988 Chevy 3500, 5.7 Stalling Problem Persists

Many of you may remember my posting this problem a couple weeks ago. I followed up on many of the suggestions you kind folks made.

Throttle body equipped engine stalls unpedictably while vehicle is at an idle. This can happen while it is in gear, in neutral, or shifting forward to reverse, (automatic transmission). Truck runs perfectly down the road and has good power.

Previous owner had MANY parts installed, (throttle position sensor, coolant sensor, EGR valve, pick-up coil and distributer, fuel pump and sending unit, knock sensor etc.) to try and correct the problem, but no luck.

The truck starts/re-starts perfectly.

Today, while the truck was idling I jiggled the wires to the pick-up coil, throttle position sensor, coolant sensor, etc. but was unable to cause a stall.

I plugged off the vaccum to the EGR--no difference.

Fuel filter is new. Last summer fuel pressure tested normal at various rpms while running in the shop, (truck has sat in garage since last October).

I did notice a lean smell when it stalled while I fiddled with in the shop today.

I could ramble on, but will respond to all suggestions/questions you kind folks make.

I'm not too techy, but this thing has me baffled.


Thank you,
Glenn FitzGerald

I had an 89 that had a grounding issue with the in tank fuel pump. replaced and still same problem... had to ground it correctly in tank. not sure if 88 had same tbi set up or not. irritating problem cause it came and went. have you checked for vacuum leaks at manifold--sensor issues?

i think there is a idle air soleniod on the side of throttle body.could be carbed up or air passsage pluged

I suggested you replace the gasket under the throttle body, don't know if you did it, all the symptoms sound lean like sucking air, stumbling at idle and running right at speed then you even say smells lean.
Here's the other thing, my 88 was doing the same thing. Good luck.

Has the distributor cap and rotor been changed or checked? Very common for these two to cause issues like you describe, as spark/fire will jump around if they fail or are manufactured with inferior quality. Pull them off and look to see if there is corrosion or obvious signs of cracks /defects/etc.

Just had a similar issue with my '97 K2500 w/ Vortec 5.7L, the cap and rotor were corroded and worn. Replaced them and so far the issue has been resolved.

Hope this helps!

Friend at work has a 95 that is doing the same thing, gm mechanics are stumped as to why it is doing it, thrown tons of parts at it, now they are thinking that it maybe a exhaust vale stuck open or has some carbon holding it open partially, or the computer is going whacky in it! Bob

Hello Glenn F.
Pullimg the vacuum hose from the EGR valve does not prove it is not the problem. You need to block the opening off with a heat resistant gasket, so there is no chance of leak in either directions. Even without vacuum the sealing may not be 100%. It may not be your problem, but this way you'll know for sure.
Guido.

Have you tried tapping on the ECM with screw driver handle while running. Or,wiggling the ECM connectors while runinng ? No codes ,correct ? What is fuel pressure and volume now ? Seen some magnatized dist shafts cause some werid intermittant problems. Did you sweep test TPS with ohm meter ? may be able to unplug it and ECM uses substitute value ,could then rule it out if still dies . Can you determine if your loosing spark or fuel ? Can you spray carb spray into Throttle body and keep if from dieing? darn I wish this thign was in my shop ,,kinda hard trouble shooting online , lol

(quoted from post at 22:55:20 08/05/11) Hello Glenn F.
Pullimg the vacuum hose from the EGR valve does not prove it is not the problem. You need to block the opening off with a heat resistant gasket, so there is no chance of leak in either directions. Even without vacuum the sealing may not be 100%. It may not be your problem, but this way you'll know for sure.
Guido.

Click to expand...

uido, you have that right! BTDT

My 99 f250 with Triton V8 did the same thing ran fine at highway speed but let off the gas it would die the idle air control sensor was bad changed that and it fixed it I"m not familiar with Chevy"s but I"m sure it has one (I"m a Ford guy but those duramax diesel sure sound mean) think I might swap before much longer I hope.....well goodluck

There was one or two years that Chevy had tubes that went inside the intake manifold and they would carbon up, but I can't remember what years they were. Chevy has made some good stuff and also some junk. I think there is a test where you apply vacuum to the egr valve. The engine should stumble if it is working properly. Just pulling the hose off doesn't tell you if it is working properly. Have you sprayed starting fluid around the intake manifold and hoses to check for vacuum leaks?

Glenn,

I had a mysterious stalling problem with my '88 C-1500, same engine. It turned out to be the distributor pickup coil, which I think you said you've replaced.

What I did was leave it a a garage that had a scope. They hooked it up to the scope and left it running until it quit. It took several hours, but when it finally quit they were able to pinpoint the problem immediately. I'd suggest you stop shotgunning the problem and take it to a garage with the right equipment to diagnose the fault.

I think they still had oodles and gobs of vacuum hoses to rot and crack in 88.

Hey Guido, I use tin foil. Gerard

Wait till you see what the Scorpian 6.7 Ford diesel does ! Monster ,and pretty indestructable , unlike 6.0/6.4

Wait till you see what the Scorpian 6.7 Ford diesel does ! Monster ,and pretty indestructable , unlike 6.0/6.4

Gerald .i wear tin foil hats from time to time too ! lol

My '89 K1500 with the 5.7 has been idling rough lately, although it's never stalled. Runs fine on the road.

The cap, rotor, plugs, wires, and EGR valve have all been replaced within the last year and a half to cure specific problems. When I get time, maybe I'll try cleaning the throttle body.

Hello ASEguy,
It works for me too!
Guido.

You are just throwing parts at this.

Have you taken it anywhere for diagnostics?

It is quite common for the torque converter to lock up and not let go. Unplug the cable and run it for a while.

My throttle body was leaking and pooling fuel in the air cleaner housing. It would die when shifted from reverse to drive due to the fuel sloshing down the throttle bores. It took me 6 months to figure that one out.

Aaron

It would pay to look at thew catalitic converter.

One of the simplest things you can do is to clean the throttle body. A procedure, with a can of carb cleaner, can be done with the TB on the vehicle.
I would be glad to go through this if you don't already know.

Jiles

Throttle body was cleaned and new gasket installed at a shop before I bought truck. TB is not leaking.

Cat converter...I removed the rear one. I haven't tested/removed front one, but it still stalls the same with the O2 sensor removed. Removed sensor would decrease exhaust restriction. I re-installed the O2 sensor.

Previous owner had the ECM scanned numerous times (and new parts installed).

I unplugged transmission and it stalled while idling in shop. In nuteral and shifting forward/reverse.

All vacuum hoses appear to be new.

Two clogged tubes in intake manifold...??

I sprayed starting fluid around TB and intake manifold. No rpm increase.

Idle air control motor sure appears to be functioning properly. First start, brings rpms up to 1200. Soon backs down to @500. When unplugged engine stays idling at 1200 rpm.

I have tapped ECM with screwdriver handle while driving truck, (glove box is out). No change. I did not wiggle connections while running. A different ecm was installed=no change. No codes/check engine. Maintains 12 lbs. fuel pressure even as it stalls. I do not know the volume. TPS runs full range. I do not remember if I tested with an ohm meter. If I did it was last summer. I have not unplugged TPS while running. I will try this. I do not know if it is losing spark or fuel. Stalling occurs suddenly without the slightest stumble/warning. I have thought about spraying carb cleaner in TB when stalling, but this may not be easy as it stalls so quickly/unpredictably.

I have EGR valve off. Will install a foil gasket in the morning. Previous owner had new EGR installed. It appears to be working properly when I watch action as I suck on a test hose.

Distributer cap and rotor = new. They still look good.

I don't think it's a fuel pump ground situation as it maintains 12 lbs pressure as it's dying. I installed in-line tester just before the filter (new).

I have had engine scanned by a skilled tech. Results were inconclusive. I may, indeed, have it scanned again.


I am seriously considering switching over to carbruetor fuel system and standard electronic ignition....




Thank you for all your suggestions/support thus far.

Glenn F.

I'm not sure what you mean by a "standard" electronic ignition. Assuming the vehicle is stock, it's already "standard". The TBI on an '88 is dirt simple; compare it with the carbureted '87 engine and you'll see what I mean.

Leave it stock, otherwise you'll just be adding new problems on top of the unknown one. Like we learned in first year algebra, it's easier to solve the problem if there's only one unknown variable.

This morning I put a tin foil "gasket" between the EGR valve and intake manifold = no improvement.

Interesting: While I had to be VERY quick, I was able to keep engine running, (as it was stalling) with a shot or ether into the TBI. I'm gonna switch the TBI & gasket out with a known working one this morning.

Thanks,
Glenn F.

1987 also had some tbi

hmmm . check resistance of injectors . warm and cold . May have winding bad in one . they make a noid light harness you can run in series to injector and watch it flash as inj is pulsed. No pulse = ecm side . pulse ,no spray = inj side . Good luck

Glenn, go through the IAC calibration instructions in your manual. It sounds like it doesn"t know home. Otherwise Your idle speed should be 700 rpm.
JB

My 89 GMC 5.7 did the same thing. Would not idle. It would just stall. Couldn"t get the problem fixed until I took it to an older mechanic who pulled the distributor out and popped a rebuilt one in. Problem gone.

I"ve had experience with 3 of these. Two of them were fuel pumps. That year uses the low pressure for fuel injection. They can measure within spec, but still be too low. Mine was like that. Had a friend with the exact same problem - was looking to buy a pickup with the same symptoms. The previous owner played the part swap game, and eventually got frustrated and listed the truck for sale. My friend bought it, replaced the fuel pump, and that was that. A coworker had one with same symptoms. His ended up being the distributor. The diagnostic codes are not always conclusive. Mine had multiple codes, including "mixture too rich", and "mixture too lean" at the same time. Try the easy (and cheap) stuff first - vacuum leak, bad ground somewhere.