What could happen? 91 ECU in a 94.

[Crashsector]

I'm still troubleshooting some A/C problems and I want to swap out the ECU for a known working one to see if that's the problem. The car is a 94 Legacy L AWD 5MT.

I have an ECU from a 91 Legacy L 2WD 5MT. I know the replacement parts for each have different part numbers, but I'm wondering if I could do any damage hooking the 91 ECU up to the 94 and seeing what happens.

Anyone have any insights on what the difference is between the computers?

Thanks!

--Andy

[wtdash]

Hi,
I'd do some more searching, but the '91 should run it fine. Check the ECU pinout for differences: http://www.surrealmirage.com/vrg3/ecupins/

Td

[Legacy777]

91 MT ECU is a Hitachi ECU, the 94 MT ECU is a JECS ECU. They use different MAF sensors, and at the very least you would need to swap the MAF sensor to a Hitachi MAF sensor (silver metal bodied sensor). The injectors are also slightly different between the 90-91 MY's and the 92-94's. The 92-94 injectors run by the 90-91 ECU's will run a little rich, but should still run for testing purposes.

[Crashsector]

Thanks for the useful info as always Josh. I actually bypassed the ECU in the A/C system and my symptoms are still there. So I'm banking on a failed/failing coil on the compressor clutch. It's the last thing I'm going to replace until I give up.

Thanks again!

--Andy