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Help diagnose engine problem...

Keitha

Keitha

1/2 ton status
 Premium
Joined
Oct 13, 2008
Posts
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Location
Costa Mesa, CA
1991 Chevy Suburban
383
Holley TBI
TBIChips chip
I was driving home from LA to Orange County at 1:am last night and got stranded by my truck. I was about 1/2 way home (around Carson) doing about 75mph. My Suburban has been running good if not a bit rich. All of a suden I felt a loss in power and heard a sputtering sound. I pulled off the freeway and the engine almost stalled, I barely made it to a gas station. When I let off the thottle the engine stalled. I was able to restart it but it ran very rough and sputtered and smoked a bit (dark smoke). It would not idel if I did not give it some thottle. The next moring I bought a new ignition module and installed it but it did not help at all. I then tried a new coil, but that did not help.
It is showing a code 42. I have checked the EST wire and it is plugged in.
Any Help???

thanks,
Keith
 
I've had that happen before to me. It has something to do with the ESC module. You might want to unplug the wiring and clean it then hook it back up and see what happens. That is all i did and all has been good ever since.
 
Here is a question:
If my module did go bad, could that cause the plugs to foul? Before I changed the module out I was trying to run it and it was smoking and misfiring. After I changed the module it seemed to be about the same symptoms. Working on it today I noticed that it cleared up a bit at higher RPMs but still missed a bit. I pulled a few of the plugs and they were black and sooty (not oily). I may try all new plugs to see if that helps.
I just took it up the street and back and power seeked OK when I got into it. When I slowed again the idle was rough but it stayed running.
 
Keith, I can't help the situation but I'm just sorryyou broke down in Carson. Glad you had no problems with being broken down in that part of town that late at night. Really could be a scary situation.
 
Big Blzn said:
Keith, I can't help the situation but I'm just sorryyou broke down in Carson. Glad you had no problems with being broken down in that part of town that late at night. Really could be a scary situation.
Click to expand...

Let's just say it was interesting watching all the peeps come and go at that gas station. I just held up under the canopy at one of the pumps.
It is very humbling to have to call your wife after 1:00am. She had to get the kids out of bed and come pick me up. What sucks is that now every time we take my Sub to Mammoth or any road trip I know she will doubt the reliability.
I guess it goes with the teritory of loving these older trucks!
 
Thanks Dorian. That is a great link.
Working on it last night I discovered a bit more. The code went away: I think it showed because I tried running it w/ the bypass unplugged to see if it would do better.
I am hopping now that my post #4 above is the correct diagnosis. I just wont have time to swap the plugs till tomorrow. Has anyone else observed fouled plugs after a module went bad?
 
I'm a cheap bastard, I'd clean the plugs up and run them. Soot doesn't hurt them, just hurts the ability (and probably not much at all based on 30,000V) to ignite the mix.

If the ECM is in limp home mode, I'd expect poor driveability across the board, and fouled plugs as it defaults rich.
 
How do you know if you are in limp mode? The SES light is not on and I am getting it to flash 12 using a paper clip.
 
I believe certain codes put it in limp. What I was saying was that perhaps the plugs fouled because of the code and the resulting limp mode.

I have no idea what codes trigger limp, I was always under the impression that OBD1 was either in limp mode or running normally, but apparently GM wasn't that black and white, and at least with certain setups, there were varying "degrees" of limp mode.

You shouldn't be in limp mode if no codes are being thrown and you get code 12, but stranger things have happened I'm sure.
 
I pulled the spark plugs and 7 of them look normal but the number 3 sparkplug looked fouled. I then put all new plugs in, ran if for a bit (it still missfired) and same thing; #3 plug looks black and sooty while others look OK. What could cause one cylender to not fire?
Distributer and roter are about 3 months old and look good. I just replaced the ignition module. The coil seems good.
thanks,
 
Check the hose to the MAP sensor and make sure it is connected properly and has no leaks. Check and clean the connector at the coolant sensor as well. The only other thing I can think of that will make it go full rich is high fuel pressure from a bad regulator or restricted return line and is fairly unlikely.
 
Keitha said:
I pulled the spark plugs and 7 of them look normal but the number 3 sparkplug looked fouled. I then put all new plugs in, ran if for a bit (it still missfired) and same thing; #3 plug looks black and sooty while others look OK. What could cause one cylender to not fire?
Distributer and roter are about 3 months old and look good. I just replaced the ignition module. The coil seems good.
thanks,
Click to expand...
Do a compresion check on #3...
 
Try swapping plug wires.....Wait a minute, let me rephrase that.
Swap the whole wire, don't just move one over<G>.

A bad wire, plug, or distributer cap could cause one to misfire.
The plugs and cap are fairly new, and are less likely to go bad than a wire.
If it were MFI instead of TBI, I'd say a bad injector.

I guess one of the two injectors could be leaking and that cylinder is just weaker than the rest and letting it flood out.
Doubtful though.

If the wire swap doesn't show it, try the compression test.
Its about as likely to show a problem as the wire change, but the wire change is easier to do.
If you had an O'Scope and a clamp on ammeter, you could do a cranking compression test.

J.
 
Thanks for the help so far. I will try swaping the wires this evening.

What would happen if I had a bad ignition pick-up?
What else can go bad on an 18 year old ditributor? I am thinking about getting a new reburbished distributer from Kragen. How would a refubed distributer compare to an MSD (or simmilar brand) distributor?

thanks,
 
Holley TBI are notorious for blowing injectors, leaking, and generally being a POS just like their carbs.
Check your injectors and see if they are leaking or obviously dumping in too much fuel.
 
Thunder said:
Holley TBI are notorious for blowing injectors, leaking, and generally being a POS just like their carbs.
Check your injectors and see if they are leaking or obviously dumping in too much fuel.
Click to expand...

Injectors seem fine. No leaks. I have the new style Holley injectors on mine and it has always done well. I don't think this is a "too rich" issue. It seems to be limited to the #3 cylender only now.
 
Keitha said:
Thanks for the help so far. I will try swaping the wires this evening.

What would happen if I had a bad ignition pick-up?
What else can go bad on an 18 year old ditributor? I am thinking about getting a new reburbished distributer from Kragen. How would a refubed distributer compare to an MSD (or simmilar brand) distributor?

thanks,
Click to expand...
It's not the distributor...
 
could the results of a bad module (misfires etc) cause the catalitic converter to go bad? What are the symptoms of a bad cat?
I might be grasping here, but I am at a loss. I have gone through every bit of the ignition system but have not yet checked compression. This motor only has a couple thousand miles on it for what that is worth. It was running good till this came on.
 
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