2 cylinders not firing...suggestions?

Nissan 300ZX technical discussion forum: Maintenance, performance, installations, modifications, how-to's and troubleshooting.
denraweb
Posts: 35
Joined: Sun Jul 22, 2012 9:43 am
Car: 1992 300ZX Twin Turbo

Post

Ok so I just changed out 2 injectors that were out of spec. After firing it up and checking over, the idle was still rough and power was still low. The injectors I changed were the right side closest to the front (I'm guessing cyl #1) and the middle left side one (cyl #4?). Anywho, i started checking around the engine bay for any plugs or clips or anything that wasn't plugged in right. I also did a diagnostic and the ecu gave me code 55, no malfunctions. While I was checking near the back of plenum, I leaned on it and had put pressure on the harness and all of a sudden the engine stopped vibrating so bad and almost sounded perfect, aside from the leaking precat. The part of the harness I leaned on is that part on the top that holds all the plugs for the coilpacks and injectors. My question is can that harness be pulled with the engine in to be inspected and repaired? I've seen a lot of mixed answers on this matter and after looking at actual oem pictures of twin turbo harnesses, I really cant see why it can't be, other than some clips holding the harness to the engine side firewall. To be more specific, this harness runs on top of the plenum for the most part, and then runs down the back to the passenger side to run inside the cabin to the ECU. From what I understand, it isn't the ENTIRE harness, it's just part of it, and I think it's called the EFI harness. Has anyone got any PERSONAL EXPERIENCE doing this with the engine in?

Also for those that will ask, all injectors and coilpacks are testing within spec.

Heres what I'm getting for cyl firing now.

When I remove injector or coilpack connectors (assuming only 1 needs to be removed to see if idle drops since BOTH are needed to fire a cylinder), 4 out of 6 cylinders drop the idle. The 2 cylinders that do nothing when either plug is removed are the first (2?) and last (6) on the left side (passenger) head. I'll use the diagram below to show my numbering.

Firewall
6 5
4 3
2 1
Front of car

^^Is that correct numbering?

Or is it like this...

Firewall
5 6
3 4
1 2
Front of car


denraweb
Posts: 35
Joined: Sun Jul 22, 2012 9:43 am
Car: 1992 300ZX Twin Turbo

Post

Oh also tomorrow I will be checking the CAS as well as the PTU. For the CAS I read that you can remove it and turn it by hand it you should be able to hear all 6 injectors firing in their order. Is that correct?

Also does anyone have the instructions on testing continuity in the injector wires to the ECU?


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