DreAded p0300 - MY350Z.COM - Nissan 350Z and 370Z Forum Discussion



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Old 11-14-2017, 12:45 AM   #1
ZRcer85735
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Unhappy DreAded p0300

I have been chasing down this misfire problem.for weeks now. Ive.done all the obvious like'm plugs , intake gaskets ,checked coils , ect. I at my Wit's End what can I do next please help me ,05' 35th Anniversary Edition stock ,spacer plate ,high-flow cats, 6speed bare minimum on the mods and a performance chip that plugs into the OBD2 port.
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Old 11-14-2017, 06:47 AM   #2
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when does the misfire occur? At cold startup? While driving?

I was getting the p0300 and i pin pointed it to cold starts. I previously cleaned out my throttle bodies and I since had a hard time calibrating them. I get the p0300 once in a while.
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Old 11-14-2017, 06:56 AM   #3
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when does the misfire occur? At cold startup? While driving?

I was getting the p0300 and i pin pointed it to cold starts. I previously cleaned out my throttle bodies and I since had a hard time calibrating them. I get the p0300 once in a while.
It happens cold or hot. As soon I erase the codes it returns. Ive replaced all the intake and plenum gaskets, cleaned and replaced MAF, both o2 sensors on bank 1, and still the ahort term fuel trim is @ 25% adding fuel either in open or closed loop. The only thing I havenr done is replace the injectors. Id l : ke ro.pin point it further before shelling out the $ for injectors. Any help is welcome. I am getting 8-10 MPG TOPs and absolutely no.power .
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Old 11-14-2017, 06:57 AM   #4
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when does the misfire occur? At cold startup? While driving?

I was getting the p0300 and i pin pointed it to cold starts. I previously cleaned out my throttle bodies and I since had a hard time calibrating them. I get the p0300 once in a while.
Both actually.
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Old 11-14-2017, 06:58 AM   #5
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Welcome - First, I would get rid of the performance chip and reset your ECU.. How many miles are on the car? Did it throw the code randomly, or after you changed something? How did you troubleshoot the plugs and coils?
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Old 11-14-2017, 07:02 AM   #6
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I have reset the ECU and it still.tripd the code right away. I have put new plugs in it twice and last.rime.one plug had the irridium tip melted. I havent checked the coils. Do.I.just.unplug them one at.a time and listen for ? Thank you for.tour feedback. Yhe coils and.injectors are m last hope in finding this problem
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Old 11-14-2017, 07:10 AM   #7
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Welcome - First, I would get rid of the performance chip and reset your ECU.. How many miles are on the car? Did it throw the code randomly, or after you changed something? How did you troubleshoot the plugs and coils?
Randomly. Nothing I have done thus far has helped or.corrrrcted the issue. Thank.You
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Old 11-14-2017, 07:29 AM   #8
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Can you check and log your AFR's?

If you are melting plugs you are probably leaning out burning your cylander. Also check your cats, my buddy just had his car doing the same thing we chased for months until I finally talked him into looking at the cats.

And one was clogged aka broken and was blocking the exhaust for one bank. Apparently it happens more often than not with these cars as soon as you start messing with breather mods.

All he changed was his air intake.
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Old 11-14-2017, 07:32 AM   #9
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Quote:
Originally Posted by Atreyu'z 350 View Post
Welcome - First, I would get rid of the performance chip and reset your ECU.. How many miles are on the car? Did it throw the code randomly, or after you changed something? How did you troubleshoot the plugs and coils?
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Can you check and log your AFR's?

If you are melting plugs you are probably leaning out burning your cylander. Also check your cats, my buddy just had his car doing the same thing we chased for months until I finally talked him into looking at the cats.

And one was clogged aka broken and was blocking the exhaust for one bank. Apparently it happens more often than not with these cars as soon as you start messing with breather mods.

All he changed was his air intake.
It's running very veru rich. The raw gas smepl is so.bad I cant drive the car. The upstream O2 sensor on bank one is is reading very high and dont fluctuate.
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Old 11-14-2017, 08:16 AM   #10
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I have reset the ECU and it still.tripd the code right away. I have put new plugs in it twice and last.rime.one plug had the irridium tip melted. I havent checked the coils. Do.I.just.unplug them one at.a time and listen for ? Thank you for.tour feedback. Yhe coils and.injectors are m last hope in finding this problem


REMOVE THAT PERFORMANCE CHIP. THEN RESET YOUR ECU.. check back.
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Old 11-14-2017, 08:20 AM   #11
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The issue started before the chip install . The chip.actually.made a little.difference in being able.to driventhe car at all .without.the chip the car won't accelerate at all but voing out yhere now.and.try that. Thank you
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Old 11-14-2017, 08:28 AM   #12
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It's running very veru rich. The raw gas smepl is so.bad I cant drive the car. The upstream O2 sensor on bank one is is reading very high and dont fluctuate.




Sounds like one of your coils isn't firing consistently, causing raw fuel to pass through your cat.
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Old 11-14-2017, 08:34 AM   #13
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The issue started before the chip install . The chip.actually.made a little.difference in being able.to driventhe car at all .without.the chip the car won't accelerate at all but voing out yhere now.and.try that. Thank you


That may be so, but I'm trying to approach this systematically. So taking that thing out, resetting your ECU, and starting at ground zero(default ecu values) is part of the process.
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Old 11-14-2017, 08:38 AM   #14
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my guess is one or more coil packs going bad
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Old 11-14-2017, 08:40 AM   #15
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Ok reset ecu and took out.chip. Runnning.very rough and very rich. Do.I pull one coil at a time.to.test ?
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Old 11-14-2017, 08:51 AM   #16
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Old 11-14-2017, 08:56 AM   #17
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With it idleing, unplug each coil one by one. If you unplug a coil and the idle changes, then plug it back in its probably okay. If you unplug a coil and the idle doesn't change, then replace that coil.
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Old 11-14-2017, 10:42 AM   #18
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and still the ahort term fuel trim is @ 25% adding fuel either in open or closed loop.
This makes me think you have an injector that's in a stuck open position. How many miles do you have on your car? Are you running with the factory injectors? Did your bad plug smell like gasoline?
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Old 11-14-2017, 10:52 AM   #19
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Well first coil I checked was bad. That plug is soaked in gas now to check.other two in tjat bank and hopefully new coils will fic the problem
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Old 11-14-2017, 10:57 AM   #20
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I didn't see the OP mentioned the chip. That would have naturally been my first guess, remove it. I have not heard anything good come from those

Quote:
Originally Posted by Atreyu'z 350 View Post
Welcome - First, I would get rid of the performance chip and reset your ECU.. How many miles are on the car? Did it throw the code randomly, or after you changed something? How did you troubleshoot the plugs and coils?
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