jordankeck

So I have been battling issues with how my 93 Z28 has been running since the day I picked it up. After a few years of on and off troubleshooting, I have narrowed the details down to a point where I am hoping that I have identified the issue as the opti. Here is a list of symptoms:

• After car has sat for extended periods of time (winter), car will start and run until engine warms, then die. Car cannot be restarted until it has had time to cool off. If car is ran daily, it will not have this issue of dying once warm. This problem has existed the entire time that I have owned it (roughly three years). I pulled the codes this spring and found a DTC 16 (OptiSpark low resolution pulse not found). This code coincides with the car stalling when warm, no longer occurs once the car no longer dies when warm.

• After removing from storage, and hurdling the first dying when warm situation, the car will run awesome for some time. At some point however, the car will begin to miss and run poorly. Performance, especially at low RPM, is poor.

• One of the times that the car had shut off once warmed up this spring, I checked spark and found that I had zero spark to the plug. As soon as the car had sat long enough, spark returned and the car fired right up.

• I have also ran through the exercise of checking fuel pressure at idle, at WOT, removing the vacuum line from the pressure regulator, and have enen checked pressure bleed off. There is absolutely no problem with fuel pressure, and my issue is all related to ignition.

• One VERY rainy/wet morning a few weeks ago, the car would start and want to die, would not idle at the designated RPM. I drove it and had to keep my foot on the gas when shifting or stopping to keep the RPM%u2019s up. The car eventually would hold the RPM (assuming the moisture problem worked itself out), but still ran like it had a miss.

• The car never ran without the miss since that rainy morning, but another morning recently the problem with holding the RPM started again. I drove the car about 20 miles, and it still had the problem. I left it sit for a few days, starting occasionally with no change. I then started it and drove it, and after a few miles the RPM would hold, but the miss was still present.

• The problem with the car running like it was missing has always came and went. There is no pattern to when that will happen, and things like rain, humidity and temperature do not seem to be a factor.

• The car has an MSD opti that was installed professionally before I bought the car. I understand this to be the 2nd time that the opti was replaced. The water pump was replaced during the first opti replacement. I have not noticed a water leak onto the opti, but I know that the water pump and/or opti oil seal is leaking. This oil could be getting into the opti and causing ignition problems.

• I have replaced the spark plugs, wires, ignition coil, and have twice replaced the ignition control module (the first one went bad and would shut off the car, the second tested bad at the end of the warranty, so I replaced it but it made no change in the way the car ran).

I data logged the car when it would not hold RPM correctly earlier this week, and have uploaded that. Can anyone with experience review that log to see if that helps connect the dots between my symptoms? I am very appreciative of the info that I have already received from the members of this site, and any additional help would be fantastic!

https://docs.google.com/file/d/0B7xg...it?usp=sharing

Injuneer

At startup, as the engine warms up, the engine is idling at 400+ RPM, vs. a target idle speed of 800 RPM (stock programming for a 6-speed). The IAC valve is commanded fully open (160 counts). Appears the IAC valve may not be working, or the idle air passage is plugged up. The "counts" are what the ECM is telling the IAC valve to open up to. There is no feedback provided to the ECM as to the actual IAC position.

Because of the low idle, your system volts are very low, less than 12V.

Later on in the log it idles closer to 800 RPM, and the idle counts are still on the high side at 94.

It goes into closed loop when it's supposed to, but then starts dropping out of closed loop. Seems to take a long time for the coolant to warm up.

The DTC is for low A/C pressure. Not really important.

Have you ever examined the short Opti harness for corrosion or damaged pins? Have you checked the plug wire towers on the Opti for corrosion?

Kevin Blown 95 TA

Sounds like the opti might be the problem, but double check the pigtail that goes into the opti connector first, cause those also go bad. If you replace the opti, see if there is a way to install the vacuum harness and that will help it live a longer life. Another good tip is to space the ICM off the head to keep the heat out of it.