Got a 91 RS, swapped out the 305 with a 355 from a chevy full size pickup. Gone through thoroughly, wiring is good after putting the new motor in.I do have gauge issues I had before the swap but I don't believe it would cause the motor to do what it is doing. It fires very rough, computer picks it up and smooths everything out but then the service engine light comes on. The motor runs for 10-15 min. then dies. Gets to a certain temp and dies. I plan on putting manual gauges in cause most of the instrument panel gauges don't work anymore. I've upgraded the computer chip to match the motor, from TBI chips.com. I've followed the list of needed things for a swap from this website, been talking to people and they have mentioned something about a piece inside a distributor that needs to be changed. How much truth is there in that? I'm hoping to get this thing going someday soon, been working on it, on and off for about 3 years. Thanks.

 

Not so much " needs" to be changed but the ICM (ignition control module) inside the dist may be tired and failing when it heats up
Very common problem with old age

Read
http://easyautodiagnostics.com/gm_ic...n_module_1.php

for how to test all your spark system

 

The fact that the CEL is coming on and you have new problems with gauges that aren't working sounds to me like you didn't hook everything up correctly after you swapped motors. Then once the car warms up and the ECM goes into closed loop it dies because some sensor is not plugged in or damaged. You might want to double check your harness connections again and pull the codes to see what the ECM is complaining about.

 

Thanks, the gauge problems were not new, had them before the swap. The 305 seemed to run fine. I keep getting the feeling that the problem is right at the end of my finger tips but just can't get it. Many times I've been wanting to just convert it all to Carb.