Here is the breakdown. 96 LT1/M6 in a 91 RS. I have run this car for 30k miles since the motor swap. No problems whatsoever.

Then I took it off the road in March to put a supercharger on. Got it running a couple of weeks ago. Other than put the charger on, I moved the battery to the back and wired some gages.

What happens is, I am running wot and it cuts out at about 4500 rpms. It has done it in 4th about 4 times and once in 3rd. Just like it was hitting the speed limiter. Not like the rev limiter. It has also made several pulls to 6k. I checked all the tables in Tunercat and they were all right. No ses light.

The speedometer stopped working once but it didn't coincide with the engine cutting off. It started working on its own.

What are some things I can check that would cause this? Other than this, the car runs excellent.

 

Im thinking it could be a coil starting to go. Although it could also be the opti. I had the same problem in my car when I first bought it. I changed the coil, plugs,wires, and opti and the problem went away.

 

I hope it isn't the opti. I replaced it not to long ago and I have no other symptoms of it being bad.

 

try a new coil and check the coil wire while you are at it.

 

Are you running an aftermarket coil or ignition setup? I know that a lot of people have had problems with stuff like that killing Optisparks. One member of my club used to have to replace his Opti every 2000 miles because of this ignition setup for his blower. He's since gone to the LTCC and doesn't have those problems.

 

I am running the stock ignition. I have Magnecore wires on it and the coil wire looks fine.

Is this a symptom of a bad coil? It cut out pretty consistent at around 4500. Noone thinks the speedo problem is linked to it somehow?

 

It is to me the symptoms of a bad coil or opti. Is the opti a gm one or aftermarket? The speedo wouldnt have anything to do with it. It could also be your icm. The easiest thing would be to replace the coil. If it is intermitant a shop will possibly tell you the coil is good. I just had another thought. check the grounds from the icm and coil bracket to see if the connection is good.
Good Luck!

 

The opti is GM. I will make sure the grounds are secure. I was concerned with grounds during the battery relocation. Up front it has a ground at the fender and one at the block. Possibly another, I don't remember. In the back, I only grounded it to the body in one place. And I took the ground strap off of the motor to the body when I put the charger on and forgot to put it back on. Does that mean the only way the motor is grounded(and as a result, the pcm) is through the motor mounts? If so, a bump could cause a break in ground.

 

So the only ground you have at this point is the one from the negative side of the battery to the motor mount? The one you removed went from the coil bracket to the body on the passenger side. those are the only 2 main grounds on the engine side of the wiring harness. You are correct in saying a bump could cause an interruption if it is loose or on the virge of loose. Reconnect that ground.

 

I wasn't clear. It "had" a ground from the battery to fender and block. When I relocated, I had to ground it to the body in the trunk well. I put the ground back on up front from the blower bracket to the frame rail. I had one from the back of the head to the firewall as well but had forgotten about that one. The theory about the bump probably isn't it. It would do it at all speeds if that were the case. I haven't had it happen in a couple of days now.

Although now, my doors will sometimes lock themselves I don't know if it is something I have done or maybe they have a bad switch.

 

I would say you have a bad ground somewhere. maybe in the car. Do you have the body control module from a 4th gen in it?

 

No body control module.