I've got a 2004 Coupe 6MT around 224K miles. I spun a rod bearing on the original motor so we recently replaced it with a used motor with ~50K miles on it that supposedly ran and drove just fine before shipment. When we first installed it, we were planning to also be installing a custom single turbo kit. We figured we should start the motor first and make sure it was good before installing the turbo. When we went to start the motor, it would simply crank then something began smoking from the engine bay. We discovered this to be due to insufficient ground contact due to the motor being painted. Once the motor was cleaned with a wire brush we attempted once again to start it. This time, it cranked and sounded like it was about to fire but it just wouldn't. I thought at this point that it could be either bad injectors (I had installed some cheap eBay 550cc "GT-R" injectors and an Aeromotive fuel pump in preparation for the turbo), so I pulled the plenum and swapped the injectors back to the stock ones. Still same results. Would crank and fire up at this point, but only for 10 seconds or so. It would idle around 500 rpm or less while mashing the gas pedal then die. Still no codes showing up at this point. I disconnected the MAF and tried to start to no avail. I swapped the throttle body with a different one and back to stock again with no difference in results and still no codes. At this point, I pulled the fuel pump back out and swapped it back for the stock pump. I made sure all the soldering was good and all the connections were correct, which they were. Still the same issue was occurring. Before the original motor went bye bye, it was running non-resonated test pipes, muffler delete, Nismo DE CAI, Blox 5/16 plenum spacer, and an UpRev 93 octane e-tune. I flashed the back to stock tune file and tried to start again with the same problem. The only differences were that every time I started the car, it would run for longer and longer and sound continuously healthier before inevitably bogging down and dying. The plugs are new, the full exhaust is installed. I've installed new cam position sensors on both banks. We're just kind of stuck now in the same cycle. No codes, will only start for one to two minutes at a time. I was able to start the vehicle enough to get the coolant temps at operating temperature and perform the idle relearn, but the issue has persisted. I've run data logs and nothing seems out of the ordinary as far as I can tell. The only slightly unusual issue is that we have killed about three batteries in the month or two that we've been attempting to start the vehicle, however I have just assumed that this is from repeated cranking with limited voltage from the alternator due to the low idle. I'm about ready to bite the bullet and pay whatever diag fees Infiniti wants to charge me, but not before I try every last thing I can do myself. I've been without my G for 4 months now and I miss it, so any help is very much appreciated. Thanks.

 

Compression test

Fuel pressure test

Idle air recalibration, throttle plate zero recalibration.

 

Also, if a 6MT are you 100% SURE you got the alignment dowel on the flywheel in the correct position.

Take the old existing cam and crank sensors from the old motor and use them since they were verified in working condition.