2005 A6 Q BNK multiple missfire, running rough all of a sudden

Discussion in 'C6 platform' started by Darryl Snover, Apr 2, 2013.

  1. Darryl Snover New Member

    Hi All,

    Seems my A6 Quattro wanted me to have a bad weekend.


    2005 Audi A6 Quattro, 4.2 V8 BNK


    Driving to church on Sunday, and felt/heard something that sounded almost like we hit a bump in the road (except we didn't), and engine light starts flashing, engine running rough. At first, I suspected perhaps a coil pack went, but when I see that there are 4 cylinders affected, and lean run, that seems unlikely.

    Other thoughts: Timing chain skip (high mileage, and small rattle at startup). I'd think MAF, but then wouldn't all 8 cylinders be acting out?

    Looking for where to start to diagnose the issue (see attached scan).

    As an aside, I replaced the telephone module some time ago, can't get it to code, so ideas there would be appreciated as well (although it pretty much works).

    Thanks very much for any/all help.

    Best,

    Darryl

    Monday,01,April,2013,17:31:27:01367
    VCDS Version: Release 11.11.5
    Data version: 20121222



    --------------------------------------------------------------------------------
    --------------------------------------------------------------------------------


    Chassis Type: 4F0
    Scan: 01 02 03 05 07 08 09 0E 0F 15 16 17 19 36 42 46 47 4F 52 53
    55 56 61 62 72 77

    VIN: WAUDL74F15NXXXXXX Mileage: 265760km/165135miles

    -------------------------------------------------------------------------------
    Address 01: Engine Labels: None
    Part No SW: 4F0 910 560 A HW: 4F0 907 559
    Component: 4.2L V8/5V G 0010
    Revision: -------- Serial number:
    Coding: 0007772
    Shop #: WSC 02335 785 00200
    VCID: 2045F75CF3C6B41801C

    9 Faults Found:
    18061 - Please check DTC Memory of ABS Controller
    P1653 - 008 - - Intermittent
    18061 - Please check DTC Memory of ABS Controller
    P1653 - 008 - - Intermittent
    17538 - Fuel Trim; Bank 2 (Mult)
    P1130 - 001 - System too Lean
    16558 - Fuel Trim; Bank 2
    P0174 - 001 - System Too Lean
    16684 - Random/Multiple Cylinder Misfire Detected
    P0300 - 001 - - MIL ON
    16685 - Cylinder 1
    P0301 - 001 - Misfire Detected - MIL ON
    16687 - Cylinder 3
    P0303 - 001 - Misfire Detected - MIL ON
    16686 - Cylinder 2
    P0302 - 001 - Misfire Detected - MIL ON
    16688 - Cylinder 4
    P0304 - 001 - Misfire Detected - MIL ON
    Readiness: 0000 0000
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    PetrolDave Super Moderator

    What fault codes is the ABS controller at address 03 showing?
  3. Darryl Snover New Member

    00526 - Brake Light Switch-F
    1 Fault Found: 011 - Open Circuit - Intermittent

    The brake pedal switch misbehaves in cold weather with a very light touch. It's on my list of things I need to replace, but since it is very intermittent, I've not worried about that.
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    PetrolDave Super Moderator

    I'm thinking that the "bump" was the ABS controller wrongly (because of the dodgy brake switch?) thinking that it needed to do an EDL or TC or ESP, and that in turn caused the lean misfire situation?
  4. Darryl Snover New Member

    At this point, I suppose I can't discount anything as a possibility. That being said, I didn't have my foot on the brake at all. We were driving on the highway, about 80kph/50mph, smooth road.

    Erasing the codes, and they immediately come back (except for the brake light switch/ABS), car continues to run extremely rough. So I'm thinking something else.

    My 'gut' is telling me I've had a chain tensioner failure. Haven't had much time to really dig in to it. Could be a stuck secondary air valve too, leaning the one side badly.
  5. Darryl Snover New Member

    After months of 'other things' getting in the way, I've finally had a chance to pull the engine and see what's going on.

    As I suspected, chain guide failure. Two of them, to be exact.

    The real culprit is the upper right tensioner guide, from which the plastic guide material apparently came loose, and promptly went straight into the exhaust cam sprocket, which shattered the plastic material. I believe that was the 'bump' I felt. That caused the chain to jump one tooth on the sprocket as well, which caused the missfire on those four cylinders.

    I'm in the process of pulling the cylinder head to check for possible valve-piston contact. I don't believe there was any, but better safe than sorry.

    I'm reading of more of this type of failure on the 4.2, as higher mileage is reached. There are now a few companies which offer a 'kit' for the repairs, of various levels from basic only, to complete with chains and adjusters. Seems like the S4 people have seen this the most, but theirs are also the first generation that have the chain drive (2004 I believe, could be earlier).

    Failures tend to be the lower guide (every engine pic I've seen has this one cracked), but that doesn't appear to be the one that causes misfires. Rather, one of the upper adjusters/guides fails, and/or the mechanical timing adjuster on the intake cam, which has a wear point where a pin goes through. Those buggers are the most expensive part too.

    Provided I have no valve damage, I'll be replacing pretty much everything timing related, as well as having the fuel injectors cleaned and balanced, rebuild the torque converter (at 175k miles, I figure it's worth it), and a very good cleaning of everything.

    On to the CARnage pictures.. (pun intended)

    Lower guide cracked and broken: IMG_0562.JPG

    Upper right tensioner, with plastic guide material missing. Plastic was found in small pieces in recess on lower left of the picture.
    IMG_0565.JPG

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