NL22 Posted March 22, 2020 Report Share Posted March 22, 2020 I have a 91 Skyline with a RB25Neo swap utilizing the Neo Harness. Vehicle was running with a Plugin Apexi PowerFC unit. I recently just switched to a Link G4+ GTT plugin. Updated the firmware to 5.6.7, calibrated all the proper sensors, make sure all those sensors were reading in the PC LInk which they were, I go to start the car and it just cranks. Checked fuel pressure, and pressure was reading at 35psi when cranking. Before I checked the trigger, I wanted to make sure the injectors and coil were firing utilizing the manual controls in PCLink. I switch on each injector at a time, 1-6 all turn on as they should. I then switch on the the ignition coils and none of them fire at all. Checked for power at each coil, no 12v power. Disconnect the coil harness and check for power at the main harness where it connects to the coil harness, no 12v power there either. I thought there maybe a bad connection somewhere so I started tracing the schematic for the power source of the ignition coils. With Key-on( no crank), there's 12v power at both pin 1,3, and 6 of the ECM/IGN coil relay. From the schematic, the relay is grounded at pin 4 of the ecu which then turns on the relay and gives 12V power supply to the ignition coils. I checked pin 4 and there is a open 12v power. If the ECU was suppose to ground that relay, Voltage should read close to 0. I checked for input voltage at pin 80 and 109 of the ECU connector, there's 12V power supply there as well. I plug the PowerFC unit back in and the car fires right up, in key-on(no crank) there's 12V at the ignition coils. I go to check pin 4 and it was reading less then 1v which means its being grounded turning on the Ignition relay, and giving 12v power supply to the coils. I then switch back to the link ECU, key-on(no crank), there's a open 12V at pin 4 of the ecu. If I manually ground pin 4, there's 12V power at the coils in key on and vehicle starts right up. At this point, I'm not sure what other inputs I'm suppose to check for at the ECU that maybe causing pin 4 not to be grounded. This is the schematic I am using, anything else I should be checking for? Quote Link to comment Share on other sites More sharing options...
XR Pilot Posted March 22, 2020 Report Share Posted March 22, 2020 Check your harness and see if you're missing pin 31 which is a 12v ignition feed. I went through similar on my Stagea RS4S and it appears Nissan omitted this pin on the later build manual Stageas which may be what your swap harness came from. Unfortunately the Link GTT plugin appears to use this pin rather than pin 24 which is present on all Neo harnesses. The fix in my case was just splicing in to pin 24 and adding an extra pin to the ECU connector. Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 23, 2020 Report Share Posted March 23, 2020 XR Pilot is correct, Pin 31 needs a +12V signal before the ECU will ground pin 4. Quote Link to comment Share on other sites More sharing options...
NL22 Posted March 23, 2020 Author Report Share Posted March 23, 2020 Checked pin 31 and there was a wire there but no 12v power. Jumped a 12v wire to pin 31, vehicle starts now. Thanks for the heads up. Quote Link to comment Share on other sites More sharing options...
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