Strange problem...SR running weird

[issanni]

This isn't my SR, but a friend of mine, I'm posting this for him. It's a very long story how we got to this point, but I'll sum it up as best I can...

It first started when he swapped his redtop sr from his previous chassis (S13 hb), to a newer chassis he bought (another S13 hb). For reference, the SR in his previous chassis ran almost perfectly for 2 years except for a minor boost leak. On the new chassis, there was an electrical problem that prevented any electric in/on the car form working (headlights, interior lights, radio, windows, etc etc) So he figured he'd put the motor in the car and then tackle the interior electrical problem later. Also, when he swapped the motor in, he also purchased a Power FC D-Jetro model, the version that replaces the MAFS with a MAP sensor. After doing all the mechanical aspects of the swap, he tried to start it. As expected, it didn't start since he knew there was an electrical problem. He fixed the interior electrical problem...the junction box on the driver side was loose. So when he tried to start it again, he noticed his fuel pump wasn't priming when the car was started and the PowerFC was smoking. He tried the stock ECU, same result...ECU toasted. Turns out what was causing the ECUs to fry was a short in the MAFS wires that he had extended in his previous installation, but since he wasn't using a MAFS, the wires were wrapped into harness and thought to be ok. So after fixing the MAFS wires and getting the ECUs repaired...the car finally runs, but runs like ****.

The car idles fine, almost perfect, when the car is first started. But after giving the engine a little gas, and revving the engine to 2k or more, the car will return to a VERY rough idle. The same thing happens for both the stock ECU and the PowerFC. Naturally, the stock ECU doesn't run very well or at all about 2k rpm (i think) since the MAFS is nonexistent, but it still idles fine and revs a little although the rough idle is more pronounced with the stock ECU, I assume becuase of the lack of a MAFS. The problem continues when the car is idling, every so often you will hear an electrical arching sound similar to the sound spark plugs make, but coming from outside the motor. The sound seems to be coming from the area of the fuel injectors or from the coil packs or towards the top rear of the motor...it's hard to pinpoint, but it's in that area. When ever this arching sound occurs, the car stutters a bit and idles a bit more rough for a second. He was thinking it's the coil packs, but after trying another set of coilpacks, his original ones were ruled 'ok'. He tested continuity between the ECU and injectors, all fine. As far as I know all the wiring is correct and tested for continuity, but I could be missing something. Another weird thing, when we were testing the coil packs, the car would idle close to normal with the number 3 (third back from the front) coil pack removed. I think the same thing happens with the number 2 coil pack, but when testing the number 1 and 4 coil packs, the engine would die almost immediately. But all 4 coilpacks are producing a spark. I'm not sure what kind of a test he was doing, but as the car was idling, he would unplug the injectors from the harness one by one for a second. From the front...the number 1 injector removed would cause the motor to stumble, injector plugged back in..engine returns to same idling state. When unplugging the number 2 injector, the stumble is barely noticeable if at all. Number 3 injector i believe had the same result as unplugging the number 1 injector. Number 4 injector I know had the same result. That's all I can really think of right now that he tried. It's just strange how it will start up fine, idle like a champ, then after giving it a little gas, it returns to a very rough idle. It could be that the ECUs that were repaired, were damaged more than we thought, but we're hoping it's not...the PowerFC is expensive to send to Japan to get checked out and fixed.

Any suggestions on what we should check or what could be wrong? We've (actually more like "he's") gone through too many baffling problems in the last 2 months, but they turned out to be minor or stupid causes. We're hoping it's something stupid this time as well.

[Nismo_Freak]

Check grounds...

[Nismo_Freak]

Also recheck the wiring...