I have a friend who has a 1993 C4 that has been down for 18 months.

The car quit while he was driving and we towed it to a "Corvette Specialist" here in Cincinnati, the guy has been working on Corvettes since 1977. He diagnosed it with a bad ECU, had the ECU rebuilt twice, each time same code, he has replaced the Opti unit twice saying that getting a good one even new is normal. Same issues. He bought a rebuilt ECU and installed it, same issues. The Corvette Specialist has stopped returning his calls which leads me to believe he doesn't know what to do either. The car will run OK for a while, then it starts running rough and losses power.

I am going to bring it to my shop at my house, put it on a lift and start chasing wiring and cleaning grounds and connections as a start. Anyone with ideas or information, please respond, would appreciate any help!

Thanks!

 

Check the wiring harness pigtail from the opti to the engine harness connection under the passenger side fuel rail cover.

 

Thanks Buddy, I will, what am I looking for? Corrosion, chaffed wire, loose connection, voltage, or all the above?

 

All of the above.

 

I have heard of many problems with corrosion in the opti connectors, so check there.

Also make sure the ignition module has THERMAL (not dielectric) grease under it. It gets very hot and will fail when the engine is warm. It has a failsafe built in, so it's usually OK after it cools down.

 

UPDATE: The car is fixed! Having never worked on these before, I spent a couple of weeks reading, getting tips from people like you guys, and looking at wiring diagrams. Found out, the "Corvette Specialist" we took it to, put an after market "Rich Porter" brand opti on it. I went ahead and chased all the grounds and cleaned each one, Checked, cleaned and tightened all the engine control connectors, check all the voltage and resistance on all the components, verified fuel pressure, etc. It all kept pointing to that opti. I had the owner get a new Delco opti, I recommended a new water pump too, (which was a good thing since the old one was leaking when I took it off). In the process, I found 2 injectors that were pretty far out of range, so I suggested and we got a whole new set and installed them. While in there we replaced the pugs and wires too. The opti came with a new style plug that would not plug into the engine harness, so we got a new style connector from the local Chevrolet dealer and since everyone had talked about this connection being critical, I soldered in the wires and used heat shrink, rather than the crimp connectors GM supplied with the connector. After getting everything buttoned up, it fired right away, before it started as an older car with the timing greatly retarded, after letting it warm up to about 180, I blipped the throttle a few times and it revved very crisply, before it would just bog down, even without a load. After running through 3 heat cycles and getting all the air out of the cooling system, I called the owner and had him come over to drive it. He was gone forever, and I was starting to worry, when he finally came back, he was ear to ear teeth, he said in the 6 years he's owned the car, it's never ran as well or had so much power. I waned to update this to point out what seams to be a very common theory, and that is use only a O.E.M. opti on these things, I know there are people that say the MSD, Accel and others are good, but this thing had (2) "Rich Porter" brands installed, and that is what I took off. BTW, with the first Rich Porter, the car wouldn't even start. Thanks to everyone who posted suggestions, I was a stone cold rookie on the C4 when I started on this thing, and I do appreciated all the input!

 

Sounds like a job well done!!

 

nothing sucks worse then getting bad replacement parts..