I am going to switch a 97 obd2 z28 m6 car to Obd1 and was wondering if I have to use a PCM from a M6 or if I can get away with a A4 PCM. I know it won't work the other way but I was unclear as to the issues of going from A4 PCM to M6. Any help will be appreciated.
Thanks,
Insomniac92z28

 

Either will work, as long as you plan on editing the A4 ecm to delete the tranny stuff. Otherwise you will get an SES light because the ECM will be looking for all the A4 crap and it wont be there... I have actually run an STOCK A4 ecm in my car without it being programmed just to get me home once and it ran fine.. Speedo was off and SES light was on but that's about the most of it...

 

I agree its a peice of cake to do. All you need is to either turn off all the A4 diagnostic codes or dump a known good M6 file into the PCM. And don't forget to swap your knock sensors out for a 94/95 knock sensor. The 96 and 97 sensors are different.

 

It's funny you bring that up. How does tuners get by selling ECM's that don't require you to change knock sensors?? Like PCMForless I believe has where they can tune your ECM so you don't have to take your stock knock sensor out. How are they doing that?

 

No, its not that they "program" the PCM to be able to work with the 96 to 97 knock sensors. What they do is they add a resistor network to the PCM knock sensor circuit so that you can use the 96 sensors. To me there is no real benefit from this other than not having to go throught the trouble of buying and installing the correct sensors for a 94/95 OBD1 PCM. I guess in another sense is that you can go back and forth from the OBD2 to the OBD1 PCM if you needed to.

Personally I wouldn't want to take the chance to take the PCM apart and to solder the resistors in place. Plus once its done if you wanted to sell it to any OBD1 owner he would either have to remove the resistors or replace his knock sensors with the later model year sensors. Either way its not a big deal. The only thing that can be a real PITA is when they get a PCM from a B body. Most of the PCMs that I have received from B body owners for repair are badly corroded, and when I try to remove the screws to disassemble the PCM the screws often break off because of the corrosion. That means I have to drill them little number 6 machine screws out and its a royal PITA. I had one that broke all but 2 screws on day! It wasn't even close to being worth while for me to repair it for the guy.

 

Ahhh that makes perfect sense then Doesn't really concern me as I have my knock sensor bypassed anyways but I was just curious how they were accomplishing that

thanks