My cousin and I replaced the head gaskets on my 01 monte carlo *3.4L*and now the car wont start. The car will crank but wont spark. I've been told it's the ECM. I have also been told its the PCM...idk what the difference is or if BOTH are on the car. I know the PCM is in the air filter box. It is not throwing a code, just wont start. Please help!