1990 Cadillac Deville Starting Problems

What you need to do is check if the engine is getting spark and fuel when it won't start. If both are present, either check to see if there is a signal to the injectors or see if it will start for a couple seconds using starting fluid.

Let me know what you find. Also, the security system will still allow the starter to engage but will shut spark and fuel off to the engine so it won't run. If your security light is staying on or flashing, turn the key to the run position (engine off) and wait around 10 minutes until the light turns off. It should then start.