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Thread: Help - Got a CEL P0300 Tonight

  1. #21
    Join Date
    Apr 2010
    Location
    Canberra
    Posts
    9,459

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    As per troy, I'd suggest new plugs... If the gap is correct on current ones, could be something wrong with the plugs themselves

  2. Default

    Hi everyone,
    Just wanted to revive this thread as I am now going through a very similar issue and not having much luck. I drive a 2011 BL Maz3 mps (completely stock not a single mod) and recently had engine light problems however have not noticed a single problem car hasnt skipped a beat. No rough idle no lag surges in driving nothing just that soul draining light. So to explain from the top. Ive had the car a little over a year and was perfect until about 6 months ago the light came on one morning upon startup. Went into paradise mazda they said car had a random misfire event of 10 recent misfires in 12 starts which they said was nothing to be worried about because it was random and not one particular cylinder misfiring so more than likely that it was a bad batch of fuel and they had cleared codes and good to go and said it shouldn't happen again but if it does come see them. I took their word for it however found it unlikely a fuel problem as i always fill up with 98 octane at either caltex or bp otr and not in the country. Anyway all was well and light stayed off until about 2 weeks ago when about an hour into a long 1.5hr drive the light came on and started flashing repeatedly. I pulled over to check everything i could think of and couldn't see any obvious issue and decided it may well be the same problem so i drove it home quietly none the less finding that anytime i backed off the accelerater or coasted down a hill the light would go from solid to flashing repeatedly for the next 20 seconds. I had someone from lube mobile coming out to service anyway so got him to check with a diagnosis tool and plugged in to find it came up with same reason code P0300 random misfire. He changed oil and filter and then said best place to start would be spark plugs so went ahead and put the expensive ngk ones in to be sure, he cleared code and took for test drive come back and it was on again. At this point he suggested possible buildup in injectors but from his research he felt more strongly it may be the cam sensor playing up as other sensor should have separate codes and should replace that but made no guarantee. So due to cost of cam sensor im on here in hope of some kind of confirmation as to what likely may be the cause? As ive said absolutely still running fine no issues just a light. Plugs are now brand new. Whats next?
    Thankyou all in advance. James.

  3. #23

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    Sucks to hear. What were the pugs gaped at?

    Sent from my Nexus 6 using Tapatalk

  4. Default

    Not sure on plug gaps i just know the mechanic said they were exactly the same as the originals that were in there but simply stamped ngk instead of mazda. Invoice says part number 95369 ngk iridium. Dont know anymore than that.

  5. #25
    Join Date
    Jun 2009
    Location
    Newcastle
    Posts
    1,413

    Default

    Random cylinder mis fires can be a mole, can be cpk, fuel system related, earths and power supplies. I suggest telling your Mazda dealer to diagnose the car following fault tree for that specific code... It's information they have.
    failing that become a vip member and download the repair manual, find the process for diagnosing that code, print it out and take it to a trusted repairer in your area.

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