P0300 misfire - Nissan 350Z Forum, Nissan 370Z Tech Forums
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post #1 of 2 (permalink) Old 04-03-2017, 11:32 PM Thread Starter
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P0300 misfire

Hello, I have a stock 03 350z I accidently double down shifted causing an over rev.
Since doing this it misfires under load, (P0300- multiple misfire) it idles and drives fine if you take it easy.
So I put new spark plugs in and checked the compression all 6 were right on 150psi.
I'm not finding any vacuum leaks, any ideas of a sensor or something that could have been affected, or I am wondering about injectors, but it doesn't seem like multiple ones would go out at once?
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post #2 of 2 (permalink) Old 04-04-2017, 10:01 AM
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Welcome and sorry to hear about your problem. By "double downshifting", I assume you missed TWO gears as you attempted to shift down? If it was a fifth to third misshift, and you hit first gear instead, you might have a BIG over-rev. It also depends on how close to redline you were when the mis-shift occurred. Did you note how far your VQ revved to?

One of the biggest problems with a big over-rev is a bent valve, or other valvetrain damage. That's something the Z's diagnostic system, or even a compression check may not detect. I doubt sensors or injectors would cause a multiple misfire, but continued misfires under load are not good for a precision built engine like the VQ.
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