I ran into this problem while toying around with the speed density system (1227730 ecm). I thought I had a prom assy. for a 92 Z28, but it turns out it was for a V6. After re-programming the EPROM with a V8 program, I was getting a cylinder select error code, and the car would not run correctly. However, I had more than a few memcals lying around for the MAF TPI systems (1227165 ecm). However, as you know, the knock module is integrated onto the speed density memcals and not on the older MAF memcals. I simply removed the prom from the MAF memcal (27c128) and replaced it with an AT29C256 (or you can use a 27C256). I then removed the knock module circuitry from one of the many V6 memcal chips I had and soldered it onto the MAF memcal package in its respective pin locations. Using a knock sensor that is compatible with the V6 knock circuit, the older MAF memcal with the new prom seems to be working fine with no codes.

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1987 Trans Am GTA WS6
-5.7L SuperRam
-4L60-E Transmission
-3.73 SRD

1988 Pontiac Grand Am
-3800 SFI V6
-125-C Transmission

1985 Pontiac Fiero SE
-3800 Supercharged
-125-C Transmission

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