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Thread: Misfire - not Coils or Plugs

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    Misfire - not Coils or Plugs

    I have a 2012 VW Golf GTI, and the past couple months it's been running rough, particularly when cold.

    My Ross-Tech cable shows it missing on cylinder 3, usually around 1,000rpm - 1,100rpm.

    I've tried:
    * Installing new spark plugs
    * Swapping coils (2 & 3, and 1 & 3 just to be sure).

    It's fine under heavy throttle and generally only misfires when I'm gently on the throttle. The car runs better once warmed up or if I after I drive it hard. Cold weather seems to make it worse.

    Any ideas what to check for next?

    [90,000 kms / 5 speed manual / no mods]

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    Super Moderator Lucas_R's Avatar
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    Misfire - not Coils or Plugs

    Probably an injector thats clogged with carbon buildup given the km's on your engine.

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    Took it to VW village - they diagnosed a faulty injector (which has been replaced) and did an injector service. I also asked for carbon to be cleaned in the air intake after doing some reading (all up $1k in repairs).

    It's now running far, far worse than before, even after a long hard drive out of the city.

    Their mechanic thinks it might be fouled plugs from the service but I'm skeptical given it's the same symptoms... I'm wondering what else it could be (boost leak, faulty sensor etc.).

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    Super Moderator VADERR's Avatar
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    If it's spark/ignition cutting, it's usually only Spark Plugs, Coilpacks, or Injectors. Replace the cheap bits first. I've had issues with all 3 and misfiring on my GTI. Every time it was one of those 3.
    Driver Motorsport Tuned | Melbourne Car Meets | Insta: @RefrigerVADERR

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    Super Moderator Lucas_R's Avatar
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    If you still have the original ignition coils at 90,000km then i would definitely replace those. $150 will get you a full set from BMR Autowerks in Auburn. http://www.bmraw.com/r8-coil-pack-oe-genuine-4-pack/

    And when were your spark plugs changed? Were they done at the 60,000km service? If they have not previously been replaced, then it might be well worth your while to spend the $80 or so to get 4x new platinum spark plugs.

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    Quote Originally Posted by Lucas_R View Post
    If you still have the original ignition coils at 90,000km then i would definitely replace those. $150 will get you a full set from BMR Autowerks in Auburn. http://www.bmraw.com/r8-coil-pack-oe-genuine-4-pack/

    And when were your spark plugs changed? Were they done at the 60,000km service? If they have not previously been replaced, then it might be well worth your while to spend the $80 or so to get 4x new platinum spark plugs.
    ^ This

    The Mk5 GTI also had a silent recall for Coilpacks.
    Driver Motorsport Tuned | Melbourne Car Meets | Insta: @RefrigerVADERR

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    Plugs were changed two weeks ago (>200kms); NGK Platinums. If I'd known they could be fouled from the injector service I could have put the old ones in beforehand.

    Thanks for the Coils link - cheaper than i was expecting so I might give them a go.

    I'm anxious of replacing everything and not solving the underlying issue though, which is why I took it in to to be diagnosed / repaired in the first place.

    One last symptom I didn't mention: if I rev and hold the throttle in a single position (like at 1,500 rpm), the revs won't hold still (i.e. they'll vary ~100 RPM either side erratically). Throttle sensors look fine in VCDS.

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    Have you solved this problem? Pull the sump off and check for metal or do a compression test on the miss firing cylinder. Sounds like you might have a dud piston.

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    I took it back to VW Village (who I would not recommend); they did a compression test and said that it was extremely low on one cylinder. They poured some stuff (resin?) into the cylinder to fill gaps & seals. Said there was 50:50 chance the fix would last, and if it didn't I'd need a full engine rebuild.

    My thoughts:
    1) VW Village stuffed something up on the original repair.
    2) I complained it was worse when I picked it up and they instructed me to take it for a long, hard drive. This is where I think the real damage occurred.
    3) I went back the following week (it continued to get worse), and it sounded like they did a hell of a lot of work (resin in the piston, oil change, new filter, testing etc.) in the 3 days they had the car. But they didn't charge me for the second repair; I find it odd any mechanic would do that if they believed the cause was attributed to the original fault.

    I can't see how a leaky injector causing a mild low rpm misfire for a couple weeks could cause so much damage. I had the car checked out when I purchased it 3kms earlier and compression was perfect. Also when I dropped it off the first time they said they would do a compression check as part of the diagnostics, and never mentioned any issues. I wonder if some foreign matter was left in the cylinder or they didn't seat the injector properly?

    I'm sure VW Village are fine with basic servicing but I would not take my car back to them again or recommend them for anything remotely complex (not that a faulty injector is complex). For starters, they shouldn't have given my car back when it was clearly misfiring from the second I started the car (after the 1st repair).
    Last edited by Neothy; 25-01-2017 at 05:29 AM.

  10. #10
    Senior Member Parso's Avatar
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    Quote Originally Posted by Neothy View Post
    I took it back to VW Village (who I would not recommend); they did a compression test and said that it was extremely low on one cylinder. They poured some stuff (resin?) into the cylinder to fill gaps & seals. Said there was 50:50 chance the fix would last, and if it didn't I'd need a full engine rebuild.
    I have never heard of this.

    I dont think coil packs given its better under load
    Maybe you need to get a camera into to the air temp sensor hole to 'check; for carbon buildup - there shouldn't be any. You can only see cyl 2 and 3 this way but its a good indicator

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