P0300 misfire - Nissan 350Z Forum, Nissan 370Z Tech Forums
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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?
Thanks.
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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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Old 08-06-2017, 05:11 AM
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If a rev-limiter were not in place the engine would have a high likely-hood of experiencing valve to piston contact. Valve to piston contact occurs when the valve cannot close quickly enough to get out of the way of the piston on an upstroke.


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Old 08-07-2017, 10:25 AM
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Quote:
Originally Posted by Herought View Post
If a rev-limiter were not in place the engine would have a high likely-hood of experiencing valve to piston contact. Valve to piston contact occurs when the valve cannot close quickly enough to get out of the way of the piston on an upstroke.
Rev limiters only work to prevent issues on upshifts. In this case, the OP says he downshifted and a rev limiter wouldn't have helped in any case. But you're right about a strong likelihood of piston-to-valve contact.

But this thread is over three months old, and the OP never bothered to respond. My guess is, he's already found the source of his problems and slunk off to either sell his problems or fix them.
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