Engine light flashing p0300 misfiring - Nissan 350Z Forum, Nissan 370Z Tech Forums
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post #1 of 5 (permalink) Old 08-14-2016, 11:35 PM Thread Starter
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Engine light flashing p0300 misfiring

iv got a 2003 nissan 350z 98,000km with cold air intake, cat back exhaust, headers, and high flow cats. driving home the other day the engine started misfiring, found code p0300, and there is a code for 02 sensor heater that is older and has not been affecting anything. So far i have changed out the spark plugs. (The back 2 were soaked with oil.) I ran the car while disconnecting 1 coil pack at a time with no noticable difference. I checked the temperatures at each header tube and they are all the same. Have a new PCV. Checked the MAF which was clean and harness is good. could not find any vacuum leaks. removed intake manifold, there were no blown intake gaskets. there is oil going in the manifold going into the rear 2 cylinders. checked the resistance at each injector and they are all the same. im at 3/4 of a tank of gas, so i wouldnt think that i got bad gas. fuel mileage appears to be ok, and its not going through any oil.
does anyone know what the resistance should be for the coil packs and if thats worth checking. i think next ill do a compression test.
The engine starts misfiring about 10 seconds after initial startup and does not stop. it constantly misfires and the only way that i can even make it driveable is if i feather the gas pedal and very slowly get up to speed or else it starts coughing.
I think im running out of things to try. Any Ideas???
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post #2 of 5 (permalink) Old 08-15-2016, 09:00 AM
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Welcome and sorry to hear about your problems. Since you've tried a lot of solutions without results, it seems like the best solution would be taking it to a dealer and having an experienced tech work on it with a CONSULT III. They can use a diagnostic tree to solve your P0300 issue without just throwing parts at the car. The key will be to find a dealership nearby with a strong electronics and VQ diagnostic background. Good luck.
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post #3 of 5 (permalink) Old 08-15-2016, 10:07 PM
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There are so many factors that can cause a misfire in a modern engine
The generic ODBII readers don't capture enough information for a focused diagnosis
Certainly a qualified workshop is the recommended approach

But if you want to tinker - some simple checks:

The oil was over the plug electrode? That's a bad start
Oil gets into the plenum via the PCV - so maybe you have some blow by - do a compression test
Replace the plugs or at least measure the plug resistance, if it's more than 0.1 ohms it's toast
Make sure the plugs are clean and set to the correct gap

How is the cat? Exhaust smells bad? That's a sign...

Run some injector cleaner through the engine - strong dosage

How did you check for air leaks? They can be very hard to detect
Spray degreaser onto pipes and joints while idling
If you hear an immediate change in engine running you've found a problem
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post #4 of 5 (permalink) Old 08-16-2016, 06:18 AM
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I also encountered a similar situation, zman1!
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post #5 of 5 (permalink) Old 08-16-2016, 10:07 AM
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Quote:
Originally Posted by shipbig View Post
I also encountered a similar situation, zman1!

So, why not fill in the rest of us on what you encountered? What was the ultimate solution(s)?
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