Successful wiring of OBDII with 1991 Engine
So a while back I did a TT swap for a customer using his 1998 SOHC 3000GT. The donor engine was from a 1991 TT. There were several additional wiring issues we had to work out since we started with a SOHC, not a DOHC, and a 3rd gen motor with a 1st gen engine. ECU and harness from the 1991 car were also used. The guy could never get anyone to pass him through VA safety/emissions inspection. We were told they MUST be able to hook-up to the OBDII port, no exceptions. After cross referencing all the wiring diagrams I finally decided to actually put the 1998 SOHC engine harness back in and wire the OBDII port as it should be, and also the grounds, and the power signals for the 1998 ECU. I did not wire any sensors to the 1998 ecu at all. Then I spliced the 1998 MFI relays into the 1991 harness and also left them plugged into the 1998 harness with the 1991 MFI relay also there, and plugged into its corresponding harness. This appears to be working as the scanner will now hook up to the OBDII port and it actually reads and comes back NO CODES. I will continue to drive it another day or two to make sure but this definitely seems to be working.
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