1990 JDM T-II Motor, modified S5 N/A engine harness, is on ‘91 GXL trying to run the car with N374 ECU. I need help in diagnosing / troubleshooting of incompatibility of running US spec S5 N/A engine harness with N374 ECU. The ECU does not allow injectors to supply fuel to the rear rotor even with HKS fuel cut defender hooked up. Another N374 ECU was tried on from a known running car with the same results. From what I understood, only time ECU would cut fuel to rear rotor was during over boost or over rev condition, but neither of these conditions have been met, it is just idle and normal driving. Currently, the vehicle is running with N351 ECU and vortech FMU please, advise steps in resolving this fuel cut issue.

 

My guess would be your "modified harness" is giving you trouble. Did you check your connections?

 

Vehicle is idled well with no vaccum leak and running strong on N351 ECU, all of engine sensors were left in placed when testing vehicle with N374 vs. N351 ECU.
If any of essential connections were left diconnected, the car would not run even with a godsend ECU. ???

Where did you get your FMIC for your car?