fergymoto

I am trying to track down an issue with my car. It has perfect fuel pressure, a healthy ignition system, new 42lb injectors. No matter what you do with the tuneup, it wants to retard .1-1.0 degrees timing at idle, and it is usually there but somewhat random. There is no noises that I can head such as a noisy valvetrain that would cause the knock sensor to go nuts. Is also will retard timing at WOT, but the plugs show no signs of detonation, at all. And lastly, the AFR stays in the 10.7 to 11.0 range at WOT which is way rich. AFR is OK while cruising in closed loop, but it is changing long and short term fuel counts a lot.

To me it seems as though the injectors are not being controlled right. I know there is nothing wrong with my injectors though, I have had 30lb SVOs, stockers, and the current 42lb Racetronix. Same behavior with all of them. I actually changed my engine harness too to be sure there was not any problems within it. The new harness was in better shape too, so between that and the peace of mind knowing there is no wiring issue, it was worth it.

I am almost certain that my car has the wrong ICM in it, because a while back I was trying to track down a problem and had swapped ICMs from several other motors I had, a 94, a 95, and my car which is a 97. Today I was thinking about this and I decided to look into if the ignition control modules were different, what the differences are, and what consequences come about when running the wrong one. I have found that 93 uses its own module, then 94-95 share, and 96-97 share. So we have three different ones.

What I cannot find any info on, is what problems can occur by running the wrong ignition module? Keep in mind, car is a 1997 car, with a OBDI computer, not OBDII

Anyone have any insight?

shoebox

All I know is the coil is a different part number to go with the ICM, so they both are different.
I don't think that the ICM could be responsible for ignition timing changes, because it only does what it is told to do by the PCM.

Injuneer

If I read that correctly, your only problem is knock retard at idle. Have you checked for a loose motor mount on the passenger side? Possibly a high voltage wire running close to and in parallel with the knock sensor wire? How much knock retard to you get at WOT?

It isn't likely you would see signs of detonation on the plugs, since the PCM is pulling timing to prevent detonation.

Then its running rich at WOT, but that could be the tune. Who tuned it? Have you asked them to lean it out?

fergymoto

I made some progress tonight. Josh (ws6terror) pointed out that my MAF readings at idle were high (in the 18afgs range). He recommended I clean it or swap it with another one, so I did. It now reads in the 10-11afgs range at idle and the car runs better throughout the RPM range. My AFR at WOT went from running in the 10.7-11.1 range to the 12.0-12.1 range. It pulls harder too.

I still have to figure out the timing issue, but I have a hunch I am going to find the problem in my passenger side headers. It sounds like they may be making contact with the K member at times. The exhaust noise follows the timing retard too. I think that is going to be it though, I know it was close. Probably only cleared by 1/16" or so.

The motor mounts are tight and I have poly motor mounts with only a few thousand miles on them. I guess I may have to just clearance the k member some if that is the problem.

I am going to quit worrying about the ICM for now, I will be going back to PA this weekend and I have one there that I know is a 96. I will change it and whether it makes a difference or not, it'll be the right one at least.

Hopefully tomorrow I can get the timing issue resolved. If I do, I'll be heading out to Mooresville Dragway to make some passes and mess with the tune.

Thanks for your help guys. I'll keep you posted

fergymoto

The headers contacting the k member is definitely the problem. There is actually a rounded spot worn into the k member and the header primary has a slight dent in it. I had no idea it was hitting that hard. All I ever heard was a little rattle here and there. Here's a pic, pretty poor quality but you get the idea. Apparently this is not enough clearance.




Once I fix that my timing issue should be resolved.