gimpsy

I have a 1995 coupe that has had a stumble or miss since I had the transmission re built, (see other threads) I took it to a GM mechanic and he hooked it up to his Tech 2 I believe and said the low resolution signal was dancing around and that meant it needed a new Opti spark. I replaced the Opti (see other threads) and when I got it running again the miss or stumble remained. I ended up replacing the opti with a Delphi that I got from Summit in the end. I talked to my buddy and he says the Opti is probably bad and should be replaced again, I plan on getting down to him to hook the computer up to see if he is getting the same bad signal this weekend. The car has not thrown any codes that I can see.

My question is what else could be causing this signal to dance around? The only thing I can think of is a bad cable from the opti to the ignition system but I replaced that or the PCM.

I don't believe in coincidence and would like to believe the opti I put on should be ok I would like to make sure it is nothing else that could be causing this before I replace the opti again. The engine is starting to run worse now I guess you could say the stumble is actually almost starting to want to stall.

Thanks in advance for any info

Art

TorchTarga94

Doesn't really sound like a low res signal to me. You will almost certainly get a code 16 when the low res side of the optical sensor starts to malfunction. In that case the power to the fuel pump is cut off and there will be no spark.

What condition are you plugs and wires in? What brand? How old? Are all the pins in the opti harness nice and straight and make good contact? Water pump in good condition? (I.E. nothing dripping out of the weephole?)

Could be a multitude of things, but the low res side of the opti is a very fragile piece, and when it quits, it will usually just quit, not give you a miss or any warning.

Paul Workman

AIR - FUEL - SPARK

SPARK:

Hmmmm.... Well, you did the right thing by having it scanned first. But, the problem seems to be in the info gathered from the Tech 1. Just for future reference, if a scanner indicates this or that is at fault, I've learned the hard way to ALWAYS verify the "findings" by a second method (scanner or whatever) whenever possible.

Anyway... So you changed the opti and the results on the (same) Tech 1 are identical as results before the opti was replaced? The chances of an Opti w/ identical fault having identical symptoms would mean you need to buy a lottery ticket soon as possible! People DO win lotteries too, and so the second opti can't be totally disregarded. But, I'd put that dish on the "side burner" for now, and look deeper. (The fact that the one thing common to both sets is the Tech 1. That would definitely be something to run down before moving on, methinks!)

The ECM is not out of the picture, but the likelihood is rare enough that I think we would be safe by putting a "bookmark" there and moving on (for now).

FUEL:

Note: some issues with fueling do not readily appear in a scan directly (if at all). And, if they do, it could be a parameter fault at a sensor that is the result of something else failing and affecting the reading, e.g., catalytic converter fault might be shown as a bad O2 sensor or visa versa.

Fuel pressure, injectors, filter(s), O2 sensors - the fuel itself?

AIR:

TPS voltage, MAF sensor, MAT?

I sound like a broken record, but only because "throwing parts at a situation until the problem goes away" is ever so prevalent in these troubleshooting threads, it bears repeating (and repeating.....). But, anyway, more info would be helpful in at least eliminating some of the AIR - FUEL - SPARK questions.

Paul Workman

Yup! beat me to the punch.

gimpsy

You guy's are saying all the things I figured, that it might not be the opti. I have gone through the FSM on this and I have to admit I can wrench and replace but troubleshooting this kind of thing I am rough at. I am going to look into a ground problem because when I swapped the Transmission I took off the grounds maybe I missed one going back on or didn't tighten or clean enough. Also the O2 sensors came out and were disconnected would they provide a faulty signal back that could make the car run like this?

Art

gimpsy

Just to close up my thread I finally gave up trying to fix this myself. I took the car to Abel Chevrolet in Rio Vista and they diagnosed this as a bad ground, they checked the resistance between the battery and the block and it was like 400 ohms. They said the paint on the new tranny was some of the problem and the connection on the grounds not on the Tranny was rusted bad. This has fixed the problem and I am happy. I would have never checked this, they came across it when they were checking the fuel injectors and couldn't get there light to work.

Art