Stephen68

Hello everyone, i have had my 94 LT-1 running for about 2 days now. When the motor is cold it starts right up with no problem at all. After running the motor it seems to run very good except i think it is running rich judging by the exhaust fumes at the rear of the car. After the motor has been ran and is warm it does not want to start right back up like when cold. It acts like it is out of time or something. I know these cars use the Opti Spark system but dont know a whole lot about them. Can anyone give me some recommendations as where to start trouble shooting or any ideas as to what it might be? The motor supposedly just has a little over 1k miles on it according to the previous owner. Thanks!.....

Injuneer

Have you scanned it for codes? Sounds like you may have a problem with the coolant temp sensor. It's telling the PCM the engine is cold, so the PCM richens the mixture for a cold start. If it's actually cold it starts fine. As the engine warms up and the coolant temp sensor doesn't read "warm" the engine runs rich. Try to start a warm engine when the CTS reads cold, the engine may not start

Stephen68

Fred, that actually makes a lot of sense to me....i have not seen any codes come up on my dash but the way the previous guy just pieced this Z together, it's a wonder it runs as good as it does. The only good thing i have going for me is the motor is supposed to be newly rebuilt and the body top side and under is 100% rust and dent free lol....Should i just replace the coolant temp sensor?

Injuneer

Check the sensor..... it's the one on the water pump housing. Rob/Shoebox has a guide to testing the sensor:

4th Gen LT1 F-body Tech Articles

If you have access to a real-time scanner, or scanning software, take a look at the coolant temps the PCM is receiving.

Stephen68

Thanks Fred, i followed his steps and the sensor was bad..already replaced it but it seems it didnt make any difference lol...time to check some more...