Guys,

I am hoping someone can lead me in the right direction. I have been all over all of the Corvette boards with little help. Three years ago I saved a 1990 Corvette 6 speed from the crusher after an engine fire. I replaced everything in the engine compartment including the engine and wiring harness. My current setup is a rebuilt 350 with a tpis mini ram, ignition is a camaro distributor with a blaster 2 coil. I replaced the ecm with a used one. I started the car and it ran alright until it got into closed loop then it threw a check engine light for code 41 and code 42 and runs rough like it has a huge cam, stalling from time to time. Since then 2 years has passed, I have checked every wire on the ecm and replaced the ecm and memcal with a refurbished one a second time. I still haven't driven the car yet and have at this point been working on it in my spare time. But I think I am out of ideas and patience. Recently I used a mail order tune company to "burn a chip" to try and cure the problem, but that was unsuccessful as well. I don't know how to proceed. Any help is appreciated as always.

DG

 

You're saying you're running a Corvette ECM with a Camaro distributor?

I assume you did a conversion to run the external ignition control module?

 

Being a Corvette (plastic), you need to pay attention to system grounds. Every ground MUST be clean and secure and all must be present. Your code 41 is cylinder select error and could be caused by bad ground to ECM. Chevythunder has the ignition diagrams for the 165, 730 and 727 ECMs and explains the code 41 as related to ECM wiring. You say you had an engine fire, was the ECM (under hood) damaged in the fire and swapped? A lot of times, people will sell the ECM without a prom. In that case, acquiring the correct prom may become time consuming and expensive so someone may have substituted a 4 or 6 cylinder prom. Have you confirmed the correct prom is present? Just a couple of things to check. HTH!

 

Yeah, an authentic 1990 Corvette PROM should have a Corvette 4-digit broadcast code on the EPROM Chip.

https://www.thirdgen.org/forums/diy-...rt-number.html

And BTW, if you swapped over to a small cap distributor, you have to alter the Spark Latency Correction values in the calibration, otherwise your spark timing will be off. Don't know if your chip guy did that or not.

 

Great advice. I will recheck all the ground. C4s tend to ground a stack of wires directly to the block. I might have some corrosion somewhere, or maybe one of the wires just isn't grounding well.

The ECM under the hood was melted, so it was replaced with an ECM from another car that came with the harness. Then the ecm was replaced a second time (I have 2) as well as the prom because I had thought the wrong ecm and broad cast code could have been the problem. From what I remember over a year ago we were very careful to select the correct broad cast code prom chip.

 

Wow, I was not aware of that. We went to a camaro distributor because the HEI was a little too large for the TPIS mini ram. I don't remember mentioning the distributor to the tuner so it is likely it was overlooked. Is this the likely cause of the code 42?

DG

 

I doubt the distributor itself is the cause. But if you didn't re-pin the Corvette harness (at the distributor connector) correctly to work the the external ignition control module, my guess is you could potentially cause it there.

BTW, I'm running a Corvette distributor with the Miniram.

 

I have an HEI distributor, so I will try swapping it over but last I remember when I did have it in there, it allowed for limited mobility. But I will certainly try again!

Thanks,

Dan

 

Yes, that's what I currently experience. But I set it up such that I get the timing I want within the window of movement it allows.