Hey all, I have an 03 350z. I was having an issue where I believe there was a short in the engine harness which was causing the ECM fuse to blow and the car would lose communication with the ECU and shut off. I tried to find the issue and also had several shops look at it and no one could find the short causing the issue (however we found many other exposed wires) - my engine harness was pretty beat up, very brittle, parts of it were melted together that we repaired, and it was recommended more than a few times to just replace it to help fix the issue and avoid future issues.

I found a harness that I was told was an 03 harness. Took mine out, put the replacement one in. However, the upsteam o2 sensor connectors are different (6pt instead of 4pt from my oe harness) AND when we went to start it (with the upstream o2 sensors disconnected) it won't start and has the same symptoms as when I was popping the ecm fuse, except that now im not popping the fuse - symptoms: car cranks, no start, car wont communicate with ecu, fans turn on, immobilizer turns light on. SO, Im thinking the harness I got was maybe a late 03 making it an early production 04, which I've read the o2 connectors are different on, so that would make sense.

My Questions:

1. Would having an 04 harness in an 03 car with an 03 ecu cause this non communication issue?
2. If yes, can I just swap an 04 ecu in it?
3. If yes again, does anyone know if Ill definitely need to reprogram the immobilizer after swapping in an 04 ecu with the 04 harness to my 03 car?
4. And does anyone know about how much that costs from the dealer? (trying to avoid calling them as long as I can to avoid the 'you need to pay us to diagnose it' especially since its a modified drift car.)
5. Lastly, any issues with swapping 04 upstream o2 sensors in my 03 car? Ive read about later years having a wideband reading and not sure if thats the case for the 04 and if that would cause an issue if so.

Thanks in advance!

 

1) More likely is that the ECU is dead
2) Yes as long as you do #3 and #5 as well
3) Yes. I can do it for you with an Uprev reflash and make it run 10X better at the same time.
4) Stay away from the dealer. Get a used ECU then flash it with Uprev to disable NATS and you're good to go.
5)You will need the newer O2's to go with the 04 ECU and harness.

 

Thank you! That all greatly helps.
Regarding #1, I was thinking that also, however, before I swapped the harness we could get the car to start and would only re-pop the fuse during drifting. Im hoping we didn't damage the ecu hooking it up to the '04 harness.
There's another 03 harness locally Im tempted to just get instead of the headache of the 04 ecu. There's an event this weekend Im trying my best to make.

 

Update: I found a 2003 engine harness and swapped it in the car. The car still wouldn't communicate. Thinking maybe I fried my ecu when I plugged the 04 harness into it, I then also got the 2003 ecu from the same car I got the replacement engine harness from. Still no ECU communication.
Checked the grounds, triple checked all connectors are plugged in, checked all fuses and relays under hood and under dash.

Looking on Youtube, tomorrow I plan to pull all the ignition coils to check condition and also pull the IPDM to check its condition as well. Also going to check battery voltage as some weird effort because I saw that somewhere.

 

Update:
Checked ignition coils and those are good. I did pull the IPDM and there was some corrosion. It didn't look too bad but decided to replace it just in case since these cars seem finicky. Got it replaced today and same issue. Battery voltage is good. Im kind of stuck at this point, not sure where to go next. Suppose its time to find an Nissan electrical specialist in Salt Lake to take it to.

This is what my IPDM looked like before I got the replacement for reference.

 

Update: I took the car to a friends shop and he found a loose connector and a bent pin for the Ecu. This got the car started and after some testing the fuse issue also seems to be repaired. However, now it is misfiring. He found oil in the spark plug tubes so due to his schedule I took it to another friend who replaced the valve cover gaskets and spark plugs. He also found a crack in the intake plenum and so we grabbed one from the junkyard to replace it. It still has a misfire but not as severe, we thought a fuel injector was bad as we had spark and we had power to the injectors. So he pulled everything back apart but injectors were spraying. We then found the ignition coil connectors on the drivers rear of the motor were swapped and that fixed the issue. Did some more test driving and everything seems to be solid! I have event this weekend that will be the final test but fingers crossed, I have a good feeling this time!

 

Issue confirmed fixed this past weekend!