bad injector maybe??

[mhplaas]

I'm a brand new fairlady enthusiast. my beautiful 1990 300zx 2+2 non-turbo seems to have a miss in one of the pistons. it's not the fuel filter, not the timing, and not the plugs. so i'm thinking it might an injector. any tips or suggestions?

[es.biggs]

Could definitely be an injector. Have they been replaced? Less common possibilities might be a bad coil pack or ptu.

You can narrow it down to one cylinder by doing the power balance test. Search on it, you will find lots of information and how to do it

Also, you can check an injector by measuring the resistance across both pins. I don't know the spec off the top of my head, but it's easily found with a quick search as well! Try, "ohming injectors"

[mhplaas]

thanks alot man i dont believe they've been replaced, but im not sure. i'm definitely gonna do some research.

[es.biggs]

Even if they have been replaced, it's still possible to have one go bad. Injectors are s*** on these cars man it's the biggest weak point under the hood IMO.

[Chattzx]

^Isn't that the truth. A buddy and I finally got around to replacing all of mine this summer. The original injectors are complete junk on these cars.

[mhplaas]

That sucks. Atleast the injectors are semi-easily accessable as opposed to most things in the engine bay. I love these cars, but daggum they are tough to work on. Haha!

[marty1mc]

First step, pull codes. Second step, clean all connectors for CAS, coil packs, injectors, PTU.

I had a bad miss on #5 cylinder when I first got my Z. It became a 3 cylinder miss in a few days. It was green corrosion on the coil pack connectors. After cleaning them and using some di-electric grease, it was cured.

[augiec]

I have a 1990 2+2 as well, 112K miles, always garaged. I had a very bad miss which turned out to be the coil over #1. Just did not fire and was obvious.
Ialso had intermitent misses, at 2-3K rpm with very little load - changed lots of stuff, but when we got to replacing the injectors it worked--car runs very well now--but something still wrong because every once in a while the engine misses badly while driving under the same condition--2K-3K RPM very light load. Dealer has suggested to change the EFI harness--not sure about that.

[DMeN Z]

Check your plug's gap. The gap for two of my plugs were off and caused a miss fire under higher loads. This under the assumption your connections are clean,timing is correct, PTU, coilpacks, and injectors check out.
PS: If you have a break in a wire or someone prior to you tried to replace a connector and its wire without properly sealing, you could have corrosion in and around the wire + solder point itself.