my friend has an 86 sc 2.8. we swapped the motor to an 89 2.8 well anyway the car wont start. we changed the distributor the fuel pump,plugs,and wires. then i got code 51 ecm so we changed that too but still nothing. can anyone help.

 

Hello 84camz28,

When you said that you changed out the ECM, do you mean that you changed the whole ECM or just the chip. Code 51 = Prom Error (faulty or incorrect prom) check to be sure pins are fully inserted in socket. If ok replace prom, clear memory and recheck. If code 51 re-appears, replace ECM.

 

changed the ecm and prom. i checked the codes and only got 12 which is beginning of sequence.also before i put the ecm in the check engine light would flash fast with the key on. after i changed it it was on
steady
.

 

Okay,

check this trouble shooting chart out and see if it helps any.

 

page 2

 

Were the 2 harnesses the same? may sound stupid but 86-89 is a big jump. I think a few things changed in 88 if I am not mistaken.

The 89 ECM is also going to want the VATS code before it starts, or possibly even before it even cranks.
So just staying with the VATS, you will need the key from the 89 ECM car at the very least. Or disable the VATS system.

Does it just crank and crank? or not even crank? If it cranks and cranks, check the ignition while cranking. If you get nada, it's the VATS from the 89 working.

Alot of people forget about little things like the VATS when changing out ECMs...

 

I thought vats didnt come into play until the 1990s

 

No, it came into effect on some of the high-end f-bodies in 1988 and on all of them in 1989.

 

Correct, it came into play because the buying public was tired of getting their new car stolen.
While it did effect the theft rate, it can be easily bypassed by someone that knows what they are doing with a simple resistor.

That is also why I mentioned the VATS thing.