I posted this problem last week under wierd engine problem. Tried alot of the suggestions, but still have the problem.
When cold, my 89 runs like a bat outta #$@#$! Excellent. After running about ten miles or once engine is up to temp, it starts running really rough, losing a cylinder. I ran it last week when temp outside were at 42 degrees and it ran great no problem. I got rid of the crappy multec injectors, did a leak down test and it was fine. Compression is excellent. New plugs, New wires, 8.5MM. New IAC, and temp sensor. Now my mechanic says he called two different chevy dealers and one told him to just replace the computer, that will probably fix it, the other said put in a new distributor and try that. He asked me how much I want to spend for trying things? I came here. You guys have helped B4. I can't just keep trying things, it's getting extremely expensive. Also, could Massair flow sensor have anything to do with this? Another idea I was given.....please help, someone else had to have this problem or know of it. Oh, one real important thing is that when you try to isolate which cylideris not firing, it's intermittent and moves around. Once we checked it was 8, next time it was 7, today it's three. And it's only there when the motor is warm. Never when it's cold. Thanks in advance

 

Have you checked for vaccuum leaks? Perhaps when something warms up it causes a leak.

Is there a certain temperature that the engine gets to when it begins to run poorly?

Does it knock?

MAF..possibly. My only experience is with a camaro which has a bad one and it doesn't run correct regardless of temperature.

 

Sounds like the OPTI is dying on you and possibly carbon build up in the cap.

Or.....distributor shaft wear.

 

Please forgive me, I'm not trying to be a smart a$$. Did you hook up a scanner & drive till the issue happens and see what the scanner sees the EEC system is doing?

On intermittant issues that maybe the only way you'll actually see what the management system sees at the time the issue comes up. Or if it will do it with the car sitting still and runing then I'd leave the scanner on it and let the car come up to temp and see what the issue yields in data reported to the scanner.

Again, I'm not trying to be a wise guy. I hate intermittants or things like that. My scanner is my new best friend ever since I bought one of these 'puter controlled vettes. My 72 was sooooo much simpler to work on!


Tom

 

Your symptoms indicate a defective spark module and/or a defective spark coil. The spark module is the most likely cause and I recommend replacing it first and driving until the engine gets up to temperature.

 

A bad water temp sensor or connection can cause this too. The ECM and dash gauge use a different sensor, so even though the gauge can be reading correctly, the ECM may be getting a false signal. A bad connection at the sending unit is very common, so the ECM thinks the motor is cold all the time. Runs great when the motor is cold (i.e. when you start it) but then runs worse as it warms up because the ECM is still adding fuel. Scanner is the best tool, but black smoke from the tail pipe will be evident too. I also agree a bad spark module or coil can do this too.

 

I don't think they hooked up the scanner while it was driving, but it was on in the shop while it was running crappy. I'll try this. There are no codes, which to me is strange. The dealerthat recommended the new distributor stated it would be due to shaft wear also, but do I need to put in a whole new distibutor? And the module seems to keep coming up in the distributor, third time I heard that so I think I'll try that too. I never thought of the water temp sensor...so it would make my car think it's cold and put in more fuel? Doesn't the temps sensor do that or are they the same? We just put in a new temp sensor. Does an '89 have an OPTI? What year did this start? I am not a mechanic by any means so I really appreciate all of you taking your time to help me. It's easy to get into thousands when you are just guessing. I'll take any ideas........

 

Get a scanner on that thing, your getting too many guesses here.
Your car doesnt have an Opti, either.

 

Yeah, but he could get one and keep in the glove box.

 

I thought it was later they had the OPTI. I'll get the scanner on it. Should it be driving at the time? If I start it cold and put it on when it runs great what will I see when it starts to run crappy? In other words, I've never personally used a scanner, so what will it tell me if I get one?

 

I can always count on a good laugh around here

 

Yes, the LT1 in 1992 was the first year with an opti.

 

You might also want to purchase a helms too. If you must get professional help, you might want to take it to a reputable dealer or mechanic. It sounds like too many parts have been thrown at the problem already.

Good luck!

 

I agree with Black LT4- I had a '82 Z28 & it ran great while the engine was cold( and the computer is out of the loop)- When the engine warmed, in about 10 minutes, it ran BAD! Brought it to mechanic friends, dealers, etc., & got the same story- "All we can do is change parts 'til we get lucky & it's expensive- My brother & I decided to remove the fuel injection (TBI) & install a 4 bbl Holley etc.- As we began disassembling we found that the twisted pair of wires going to the temperature sensor in the radiator( I believe) had brittle insulation & the exposed wires were shorting & sending bad info to the computer, which tried to compensate for the bad info by making corrections to the fuel & everything else - No problem when eng. is cold, only after warming-

 

Are you sure you don't have a clogged cat?

 

Or a gunked up EGR?
This you can test/clean cheaply. Take it out and see if the pintle valve moves freely. Also clean the carbon out of the opening and off the valve.

 

Thanks for all the great ideas guys. I'll get on them tomorrow!! I'll let ya know how it went.