91 c4 stalls when warmed up
 

Hello any advice would be great. I have a 1991 corvette L98 base with the automatic transmission
I’ve been experiencing some issues with stalling and misfiring. I replaced the head gasket and it ran decent before I replaced the head gasket.

It misfires really bad when the engine is cold but slightly improves when the engine is warm. However when it’s idling when it’s warmed up the car can’t seem to find idle and ultimately it decides to shut down and stall. I also have an issue where whenever I shift it into reverse and drive after the engine has warmed up it stalls. I don’t think this ties into it but I do also want to mention I’m 100% sure I have a bad catalytic converter because I can hear knocking coming from it.

The car also seems to be running pretty rich. I want to try to diagnose it before throwing any money at it so any help would be greatly appreciated.

If your coolant temperature sensor is bad it will not properly show higher temp and keep fuel rich when car should be leaning out for closed loop. That will cause car to stall. When i had my 91 had this happen. Replacing the CTS was easy even for my big hands. Just be careful pulling the connector because it will probably be brittle due to age. I say that because I did break mine getting it off and had to replace it.

I was kind of thinking the coolant temp sensor could be the culprit but would the coolant temp gauge still work even if the sensor is bad?

Yes, the CTS sensor in front of block is not the one that is used for the gauge.

Alright thank you. I just bought the sensor I’ll do an update when I install it and take it for a drive.

So I ended up changing the sensor and they both looked the exact same but when I went to start it to test the new one it would crank but not start I’m so confused

One really good tool to have is an OBD1 scanner. You can then see all the sensor outputs and how the ECM is reacting to them.

Only other things you can really do is check spark timing and fuel pressure.