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  1. #1
    Established Member Two Rings
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    Borescoped the cylinders- what does this mean?

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    Been chasing a bank 2 misfire for a couple of months and finally got around to borescoping the cylinders today: https://www.dropbox.com/sh/fpbk9wo7c...qL645juJa?dl=0

    how would you read these?

    Not seeing a ton of scoring, but lots of caking atop all cylinder heads. See some pooling of liquid (oil?) across bank 2 cylinders so i'm guessing this is related to my misfiring (symptom or cause). Compression is 140-150 across bank 1 cylinders. bank 2 cylinders range 125-150. Bank 2 breather hose had lots of sludge.

    This thread has more background on the misfire saga: http://www.audizine.com/forum/showth...gh-rpm-misfire

  2. #2
    Veteran Member Four Rings q_dubz's Avatar
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    So you have more than a 10% difference from the lowest compression cylinder to the highest? Can you post each cylinder's compression value please?

    You're clearly burning oil. Valve seals and/or guides are shot which leads to oil pooling onto the pistons. No real scoring.

    This is why borescopes are BS. They dont effectively relay the severity of an issue.

    Your cylinders look like mine did. Rings are wearing out. Side effect of the 16~18% silicon in the block alloy. It's abrasive

    Expect sludge in the breather hoses as a result of the blow-by increase.
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  3. #3
    Established Member Two Rings
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    Here are the compression numbers I got

    1: 140
    2: 145
    3: 140
    4: 145

    5: 125
    6: 135
    7: 135
    8: 150

  4. #4
    Veteran Member Four Rings 65vetteC6's Avatar
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    Quote Originally Posted by b57 View Post
    Here are the compression numbers I got

    1: 140
    2: 145
    3: 140
    4: 145

    5: 125
    6: 135
    7: 135
    8: 150
    Can you do a leak down?

  5. #5
    Established Member Two Rings
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    Won't be able to spend that kind of time on the car for a couple weeks, but a leakdown has been on my list.

    Can the oil burning / leakage point to a cause of the misfiring? (or is it just a symptom of it)

  6. #6
    Veteran Member Four Rings q_dubz's Avatar
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    Quote Originally Posted by b57 View Post
    Won't be able to spend that kind of time on the car for a couple weeks, but a leakdown has been on my list.

    Can the oil burning / leakage point to a cause of the misfiring? (or is it just a symptom of it)
    Sure. Oil burning fouls plugs with carbon.
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  7. #7
    Veteran Member Four Rings q_dubz's Avatar
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    If you have oil in the spark plug holes, then your valve cover gasket is leaking which will cause a coil to miss. You also could have a cracked wire in the harness (typically around the connector) get some cheap copper NGK bkr6e plugs and Gap them to .032 then see if the problem goes away. If it does then it's carbon fouling. If it doesn't then it's coil or wiring.
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  8. #8
    Established Member Two Rings
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    Ah...we're getting warmer. Def lots of oil in the spark plug holes of the misfiring bank. I already have a gasket sitting around so will pop it in when I have a cpl hrs this week.

    Can you explain some more about why / how the cheap copper plugs will help in diagnosing source of misfire? Btw, the entire bank misfires but only at high RPM.

  9. #9
    Veteran Member Four Rings q_dubz's Avatar
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    Quote Originally Posted by b57 View Post
    Ah...we're getting warmer. Def lots of oil in the spark plug holes of the misfiring bank. I already have a gasket sitting around so will pop it in when I have a cpl hrs this week.

    Can you explain some more about why / how the cheap copper plugs will help in diagnosing source of misfire? Btw, the entire bank misfires but only at high RPM.
    As simply as possible, your current plugs look a little fouled. So either you clean them with a stainless wire brush (which doesn't always work) or you get some cheap ones to swap in and test.

    As rpm/temp goes up dwell time (time to full charge) can decrease, so the coil isn't charging to max voltage because there's not enough time before the next ignition event.
    It's not a defect. It's normal for more modern ECUs.

    Swap the plugs, change the gaskets. Make sure the ground on the fire wall next to the brake boost hose is tight and the wires aren't shredded. Make sure the ground below the TB on the back of the pass.side cylinder head is tight and the wire isn't shredded.

    Then, try again.
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  10. #10
    Established Member Two Rings
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    Quote Originally Posted by q_dubz View Post
    As simply as possible, your current plugs look a little fouled. So either you clean them with a stainless wire brush (which doesn't always work) or you get some cheap ones to swap in and test.

    As rpm/temp goes up dwell time (time to full charge) can decrease, so the coil isn't charging to max voltage because there's not enough time before the next ignition event.
    It's not a defect. It's normal for more modern ECUs.

    Swap the plugs, change the gaskets. Make sure the ground on the fire wall next to the brake boost hose is tight and the wires aren't shredded. Make sure the ground below the TB on the back of the pass.side cylinder head is tight and the wire isn't shredded.

    Then, try again.
    Glad I asked, thanks. I did swap in new plugs after I borescoped. Problem still there. Will check out the wiring / ground tomorrow. Anyway to test resistance at the coils?

    Could a rich mixture be a cause here? Misfiring bank is running rich (Or would that just be a consequence of the misfiring?)

  11. #11
    Veteran Member Four Rings q_dubz's Avatar
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    what happens when you dont burn all the fuel?

    if you want to rule out coils, swap them to the other bank and vise versa....
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  12. #12
    Established Member Two Rings
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    Quote Originally Posted by q_dubz View Post
    what happens when you dont burn all the fuel?
    so let me see if i have this right: bank 2 burns / leaks oil into the plug or cylinder --> resulting misfires --> bank 2 O2 reads exhaust as rich. this might explain why i'm simultaneously misfiring and "running" rich


    if you want to rule out coils, swap them to the other bank and vise versa....
    I did, no change

  13. #13
    Veteran Member Four Rings q_dubz's Avatar
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    Quote Originally Posted by b57 View Post
    so let me see if i have this right: bank 2 burns / leaks oil into the plug or cylinder --> resulting misfires --> bank 2 O2 reads exhaust as rich. this might explain why i'm simultaneously misfiring and "running" rich


    I did, no change
    then follow the rest of the steps i outlined above. Too much thinking, not enough working
    Boost EVERYTHING!
    B7 S4 Turbo 4.163L BHF <<<CLICKY ;) #willraceforcookies #gapcity #gapcounty

  14. #14
    Established Member Two Rings
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    point well taken. with a 2 year old and 60 hr / week job, trying to study up ahead up of the next chance i get to work on the car.

  15. #15
    Established Member Two Rings
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    An update here from OP-
    - changed the valve cover gasket (major PIA since i stripped the back corner bolt - added 3/4 hrs to the job) -- no change
    - replaced the fuel filter (it had 50k miles on it) -- no change
    - borescoped the bank main cats -- looks clogged and that's making me think this is the culprit. Plan is to gut it and see how the car reacts

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