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    Thread: MKIV VR6 Misfire... need help diagnosing

    1. Senior Member mujjuman's Avatar
      Join Date
      Jul 29th, 2004
      Location
      New York
      Posts
      20,985
      Vehicles
      2001 VW Jetta VR6, 2006 VW Jetta 2.5
      06-12-2019 03:56 AM #1
      Hey everyone, I have not posted in these forums in years. I still have my 2001 Jetta VR6 5MT which I bought brand new.

      So earlier today, I made a stupid mistake. I was in 3rd gear going downhill pretty slowly, and I slowed down even more because the road was VERY rough and I needed to go over the rough patch of road slowly. I THOUGHT I was in 2nd gear but I wasnt. Anyway, while slowing down, I kept it in 3rd gear and slowed down enough for the engine to start bucking a few times (oops!). Essentially, the engine was lugging for those 2 seconds. Upon realizing this, I quickly pushed the clutch in until I cleared the humongous pothole, shifted into 2nd, and gradually accelerated back to speed (30mph).
      However, my engine immediately began misfiring very badly. I thought it may have been a "glitch" because of how low the rpms got below idle so I cleared the codes, restarted, even disconnected the battery to "reset" the ECU but the misfiring is still there. The codes are P0300, P0302, and P0306 pending. I am also smelling a strong sulfur rotten egg smell which I am thinking is the unburnt fuel.
      What could have went wrong while the engine was fighting to stay alive as I was slowing down in gear and the engine speed dipped below idle? It only happened for a couple of seconds.
      I was thinking timing, maybe coilpack and wires? Not sure if this would cause the coilpack to get damaged.
      The timing chain and guides were replaced 2 years ago and the engine ran strong all day today until the incident. It has 216K miles. Spark plugs were replaced last year @200K. Oil change a month ago @215K.
      I am planning to check compression in all cylinders, check to see if coilpack is arcing, check wires to see if they are arcing, and check the condition of the spark plugs in case they somehow got damaged. The engine has misfired like this in the past if I run 87 gas in there especially when it's raining out so I only run 93. When I run 93 it has not misfired rain or shine (previously, before this incident).

      What other steps should I take to troubleshoot this? Please help this is my baby
      mujjuman

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    3. 06-14-2019 04:41 PM #2
      It could be a problem with your vacuum system, my MK4 VR6 has a split in the vacuum hose from the brake booster to the intake manifold and i was having a lot of problems with it misfiring.


      Sent from my iPhone using Tapatalk

    4. Member
      Join Date
      Jul 13th, 2001
      Location
      Oakland, CA
      Posts
      4,659
      06-14-2019 06:12 PM #3
      You didn't say whether the misfire occurs at idle, but if it does, try disconnecting the connector to the MAF sensor while the engine is running. If the idle improves, the sensor may be faulty.
      Kenji

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