Subject: 1993 3000GT SL
Question:

Hello,
I have the typical starting problems that point to the ECU failing...starts sometimes, not firing 3&6, and even have a CEL that reads 12Volts constant which means Bad ECU.
Is the CEL code absolutely right or could a sensor be shorting something that makes the ECU send that code?
When the CEL is OK sometimes, no bad codes are sent 12volts-0volts-12volts-0volts, over and over meaning normal operation....this is when it isnt firing cylinders 3&6,
Could the PTU (ignition module) be so bad or shorted that all these errors are showing up.

Thanks so much ...havnt been able to drive my car for a month now...miss it alot
Answer: Thor,
It's possible your ignition coil could be malfunctioning, but this sounds like an ECU issue. You can read more info about the poor ECUs Mitsubishi put in their early 90's cars and places you can check for replacement and rebuilds:
http://90gsx.com/eclipse/cap/caps.htm

It's pretty easy to pull your ECU and visually inspect it for damage. If the ECU does show signs of damage, have it replaced. Sometimes eBay is a good place to find a working, used ECU to replace yours at a low cost.
Good luck!