Nissan 300zx Misfire

[Damien Hill]

Hey Team,
I have recently purchased a Nissan 300zx Twin Turbo with 164,000km on the clock. I brought this as a project to do up. I live in New Zealand and drove the car 9hours back home after I brought it. When I picked it up, the engine was running fine, however after stopping for a break half way, I noticed it had developed a misfire at idle. Having been at highway speeds for so long nothing felt wrong. Back to highway speeds and you didn’t notice it.. From then till now it’s missing at idle.

What I have done:
-New Plugs
-Cambelt, Waterpump, Idlers & Tensioner
-Bleed Cooling System with fresh coolant
-Oil / Filter Change

I have also done a Compression, Leak Down and Power Balance Test. Here are my results.

For the compression test (This engine is a V6) One side had all three cylinders at 140psi and the other side was two cylinders at 150 and one at 100.

For the Leak Down test all cylinders were in the good half of the green, including the one which was picked up at 100psi – And yes I had each cylinder at TDC on the right stroke while testing 🙂

Power balance test was interesting… all cylinders made a significant difference when individually unplugged. But when I unplugged the suspect cylinder the miss was more of a smooth miss. So it’s sort of firing off and on. I swapped the coil packs around but it made no difference.

Overall I was hoping someone would have an idea, because I am confused that the Leak Down test came back ok. What could cause something like this? There was no leakage anywhere?

Here is a video of the engine running, hopefully the sound is good enough to hear –> https://www.youtube.com/watch?v=XYNHgxiClQc

(Yes I know it has an exhaust leak 🙂 )

Many Thanks!
Damien

Topic

[college man]

I don’t no the year but 142 is the minimum 186 is the standard.
Try a wet test to see if compression comes up. If so rings if not
valves. Either way the low cylinder is a problem.

[Bill]

Try moving the spark plugs around. If it’s the same move the injectors around. Check for vacuum leaks around the cylinder that’s misfiring.

[EricTheCarGuy]

Injectors are a common failure on Nissans. The cylinder you found during your power balance may be a prime suspect for that. That said, misses at idle but not at high rpm are usually vacuum leaks. You didn’t mention checking for those in your description. More information on solving performance issues like this here.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

Good luck and keep us posted.

[Author]

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