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Help on diagnostic flow for multiple cylinder misfire with no codes or p0300

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3 years 5 months ago #43506 by Vtorr46
Need some advice or maybe a flow chart when checking multiple cylinder misfires no codes. Least invasive to most. I usually start with frp, 02 sensor voltage, sft ,lft, maf. But almost always check fuel pressure at idle and under load, spray intake and surrounding hoses and check plugged exhaust. Has seemed to work for the most part. I would like any advice on a diagnostic flow path I could follow every time as keep me from loosing money on headaches. Currently this week I have 2 vehicles with multiple cylinder misfires one with a p0300 and another with no codes one is at idle the other is under load.

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3 years 5 months ago - 3 years 5 months ago #43510 by Patrickreaves
when i have a misfire and no obvious culprit , i normally do plugs and wires first. make sure they are good before i try to find an issue with the other ignition components.
How often is the misfire? if its a dead miss or very consistent miss, i would do a cylinder drop test to try to identify which one is misfiring.
Last edit: 3 years 5 months ago by Patrickreaves.

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3 years 5 months ago - 3 years 5 months ago #43514 by Tyler
With any misfire concern, I usually check Mode $06 counts right after the code scan. Especially on cars 2008 or newer. Older is hit or miss.

A decent example was an 09 370Z I saw a couple weeks ago. Started out like this:



So bank one has some kind of timing problem. No surprise there. :silly: But what about the P0300? Related or unrelated? Mode $06 says:



All the miss counts are on bank one. Not all that random. ;) Very likely related to the timing problem. Fix the timing -> Fix the misfire.
Last edit: 3 years 5 months ago by Tyler.

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