I have a 1994 Z28 (1LE Package) that I ordered from Chevy in 1994. I have driven this car for 25 years and about 125,000 miles - almost 100% bone stock. Best car I have ever owned! The car has been absolutely perfect until recently. I had to replace the Opti-Spark ignition a few years ago when it totally failed. I have not been able to get the car right ever since. The first replacement was an OEM Opti-Spark that lasted for less than 1,500 miles and failed. I replaced it with a GM replacement Opti-Spark that lasted for less than 1,000 miles and failed. I replaced that with an MSD Opti-Spark recently and put the car back on the road. It runs like a champ from cold start to about 120 to 130 degrees, then the motor idles rough and runs like junk. When you try to accelerate the motor stumbles and staggers and it takes forever to get up to speed. It runs slightly better at higher rpm, but at 1,000 to 2,500 rpm it is total crap. We have since replaced the air intake hose to the throttle body, installed new fuel injectors, new spark plugs, and checked for evap and vacuum leaks - repairing all leaks that we could find. We checked the Mass Air Flow Sensor and it is good. There are no check engine lights or computer codes showing. Still no improvement. The mechanic wants to go back and look at the ignition system again to see if it is bad. I am really tired of the problem and just want my Z28 back. Does anybody have any suggestions or a diagnosis?

Thanks....

 

Thanks, Tony. We replaced the coil and the ICM checks out OK. I guess we go back and look at the MSD unit again.
This is frustrating. I absolutely love driving this car, just can't get it back to 100%.

 

Thanks so much, Tony. I will give that a try and get back with you. The two most confusing parts to me is that it runs great when the motor is cool. After it reaches 120 and up, it runs like crap. It seems to me that if the Opti-Spark was bad, it would not run right at any temperature. The second confusion is that as bad as the car runs at temperature, I don't get a check engine light.

 

I know it's been a little while and I am getting older lol, but haven't a few people had this sort of issue and it had to do with the temp sensor in the water pump being faulty causing issues with the computer from wrong readings?

 

The bad opti codes don't turn on the check engine light, so a scan should be done as normal procedure. MSD optis have had continuing problems.

 

i have, worst 26 dollar problem i've ever had!

 

Thanks much! I checked with the mechanic and he said that he checked both sensors and they were good. I guess we go back to the MSD Opti-Spark and check it.

 

Thanks. Can anyone suggest the best option for the Opti-Spark. I have tried an OEM (non-AC Delco), and AC Delco, and the MSD. So far none have worked well.

 

Does anyone have experience with the ACCEL unit? I found two versions of their Opti-Spark - a replacement for Opti-Spark I (1993-1994 LT1) and a replacement for Opti-Spark II (1994-1997 LT1/LT4). Not sure which one I would need - my car is the 1994 LT1. There is only $10 difference in these two units.

Thanks.

 

Thanks!

 

You should have the spline opti being as yours is a 94. Also, lining up that spline is not the easiest in the world, so be prepared to get a little agitated lol.

 

Thanks. I have found Opti-Spark replacements made by AC Delco, MSD, and ACCEL. Some vented, some not. Does it seem to make any difference which brand is used or if the vented or non-vented is used?

 

95 was the first year for vented, but I think they make hybrids now since they are all basically aftermarket parts now a days lol. You will need to find a splined unit and if it's vented, well that's just a plus lol. As for the Access, back in the day they were not very reliable, but may be better now, but I doubt it lol.