Ok Here is what I was I got the car from some guy. He had a 305 but put in a 350. do I have to change the ECU (computer) in the car too. Cause my car was working fine the other day. then in just died on me. If I hook up the OBD 1 scanner to it the car will start. But if its not hooked up then it just wont start. Does anyone know what this could be?

 

First, what type of scanner ar you using? If it is simply a code scanner, you are not doing the ECM any good by starting the engien with it connected. If it is a data scanner, follow the instrument manufacturer's instruction and connect the scanner only after the engine has been started (usually).

If the engine has been changed to a 350 from a 305, you do not need to change the entire ECM, but the MEMCAL needs to be changed. If the injectors were changed to the appropriate size for a 350, a stock 350 MEMCAL shuld work well. If the injectors from the 305 were used with he 350, a custom PROM is required in the MEMCAL.

When you connect a data logging scanner with the engine running should do nothing to change how the ECM operates (mode). Connecting a simple code scanner (or grounding the diagnostic request terminal in the ALDL connector) it invokes Field Service Mode. If the engine is running while in this mode the ECM will flash the SES lamp rapidly and constantly. The ECM may or may not enrich the mixture in this mode.

Which are you using?