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Help! P0300 misfire giving me headache!


JoshTSquared

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As the title suggests... 

 

I have a rev up 350z with 133k miles on it which had a misfire when we got it. The check engine light flashes from start up and sometimes disappears under load but the car sounds like it's missing a cylinder.  It sounds really rough, although it doesn't stall or splutter. A weird point to note is unplugging coil makes NO difference to the sound or speed of the idle. None. No matter which cylinder. Which seems mental to me. And I've checked that the wires for cylinder 4 and 6 are the correct way around.

 

Cylinder 3 had a particularly black spark plug but changing all coil packs, all spark plugs, and the injector on that cylinder didn't make it go away. We've replaced the PCV valve, tried a working MAF sensor, removed and inspected the flywheel (incase it was a timing thing), changed the fuel pump, none of this worked. 

 

We compression tested it dry and all cylinders were consistent (at the lower end psi-wise but within the limits according to this forum), and the only code it throws is p0300, nothing else.

 

I'm really struggling to understand what's going on here and really need some suggestions for what to try next 

 

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My thoughts would only be informed guesswork.

 

if I had the car physical I would plug into diagnostics and run a few checks, which is the same as what TDI North would do.

 

Do not expect TDI North to give you any pointers as to what the fault may be as that is how they make there money, in diagnostics and repairs.

 

TDI North will want you to book the car in with them for a chargeable diagnostic test.

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Bumping this thread because I managed to get my hands on a proper Snap on OBD reader and got these readings while the misfire was occurring. Can anyone help interpret this or does anyone know if this points to anything in particular? One of the O2 sensors on bank 2 is jumping between rich and lean very quickly

IMG_20191115_164226.jpg

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