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Thread: Misfires On all Cylinders - Help

  1. #1
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    Misfires On all Cylinders - Help

    So the car developed some rough idling a couple weeks ago, does not appear to have an issue when driving (power is good). Only when stopped or in park. Decided to do a plug change as it had been a while. Also cleaned MAF's and new airfilters - well misfires still happening. CEL starting blinking, ran Vag Com and came back that all cylinders have random misfires. No other codes. Gregg (fellow RS6 owner) came over a we looked at some measuring blocks and initially saw cylinder 4 having a higher count of misfires, but then another also showed a higher count than the others. Car also smells to be running rich (car always had a somewhat "rich" smell even before this, but now much stronger as it is obviously misfiring). So one question, would 1 bad coil pack cause a cascading effect to influence all others to act up? It seems unlikely that all 8 packs have or are failing at the same time. Also if a coil pack is bad, shouldn't the misfiring occur under load? Another comment was maybe bad gas - (always gas up at the same place), I could add a bottle of de-moisture treatment and see if that helps ??? Just a bit puzzled.

    TIA - Scott

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    Registered User lswing's Avatar
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    Cam chain tensioners. They have been failing on all cars due to age and mileage. They are brittle and crack, cam timing gets messed up, causes misfires and flashing CEL. It happened instantly to me one day, only on passenger side, but drivers was close to failing also.
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    How big of a project is it to replace them ( I do have a new set)?

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    Quote Originally Posted by cruzanrs6 View Post
    How big of a project is it to replace them ( I do have a new set)?
    You can get new pads for $40. Now labor is miserable, especially passenger side with SAI in the way. It was $2500 labor for me at $100 hour, had a few other things done. Engine in full service position. I just replaced the whole units, even though no solenoid errors, just don't want to pay labor to get back there for another 10 years. Total bill was $4,500 with other small things done.

    It only took them about 2-3 hours to open it up and find the destroyed cam tensioners. But I got no codes directly as it's just plastic breaking. Just misfires and flashing CEL, only on passenger bank though. Would be odd that both yours failed at once, but I would believe it.
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    Regarding the misfire, it was hitting all cylinders a bit, but #4 a lot, and #5 a decent amount. For example, when actively watching the misfire counter it would look approximately like this:

    #1 - 5
    #2 - 3
    #3 - 3
    #4 - 35
    #5 - 25
    #6 - 7
    #7 - 2
    #8 - 1

    (all rough examples, but the general ratios are correct)

    The misfire counter seems to automatically reset to zero every 30 seconds or so, and if we revved the motor to around 3000rpm and let the counters reset, they would stay at zero until we let the rpm drop. Engine seemed to be running fine at the higher rpm and power seems normal.

    It's a weird pattern which doesn't seem to point clearly to a specific component failure. I've seen coil packs fail in groups, but not 8 at a time!

    Also noteworthy was there were no other codes in VAG COM. I also recall that ignition timing seemed to moving around a lot when we watched it at idle. I need to scan my car and see what the timing does there to get an idea of "normal".

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    Registered User lswing's Avatar
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    I forgot about doing a quick look at the timing at idle. Forget the exact block numbers to log or look at. Here's mine from a few years back, I know there are other threads. "Passenger side was reading 16, failed drivers side reading -7..."

    I would find a few more threads just confirm where the timing numbers should be at idle, besides my old thread below.

    http://www.rs6.com/showthread.php/31...-are-the-codes
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    Timing will jump a lot from 0 to positive numbers, that's tq reserves working.
    Check VCDS blocks 91-92-93 for cam tensioners. I don't buy the "both broke at once" theory.
    Take a look at "idle" reading, then rev her up and take a look at VCDS again.

    Also, your cylinders with highest misfire count are on opposite sides of the engine. Can it be, that one of the tensioners failed and caused general AFRs to shift so much that the whole engine is suffering? Doesn't sound likely, there are 2 separate lambda control loops "per bank"...
    Can also take a look at lambda control with VCDS, to see how much AFR adjustment you're getting.

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    Quote Originally Posted by nubcake View Post
    Timing will jump a lot from 0 to positive numbers, that's tq reserves working.
    Check VCDS blocks 91-92-93 for cam tensioners. I don't buy the "both broke at once" theory.
    Take a look at "idle" reading, then rev her up and take a look at VCDS again.

    Also, your cylinders with highest misfire count are on opposite sides of the engine. Can it be, that one of the tensioners failed and caused general AFRs to shift so much that the whole engine is suffering? Doesn't sound likely, there are 2 separate lambda control loops "per bank"...
    Can also take a look at lambda control with VCDS, to see how much AFR adjustment you're getting.

    Do you know off the top the measuring blocks for the fuel trim (lambda) on the RS6 ?

    Thanks

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    Gregg, the misfire counter resets after something like 300 or 500 misfires, starts over at zero. I'm following this as it is probably different from my issue. Haven't been able to do any runs on the car with the unusual amount of snow we have gotten. After the car sitting for almost 3yrs it fired up in seconds. Idled great. After a few runs it developed a misfire all cylinders on Bank 2? Shared Plenum so I figure it can't be an intake issue but either fuel or spark. Recently I just started it up and it seemed to have migrated to only cylinder 5? I've now drained the fuel (Almost 3yrs old) and replaced with Ethanol free 93 (Euro about 99~100) Octane. Going to confirm this week if it is spark or an injector.
    Cruzan, with all that said are you sure your intake was seated well? With the MAF's connected electrically and misaligned you will get a miss. You can either re-/seat them and check or just unplug the MAF's and check the misfires. Could you have gotten bad fuel, of course with our general crappy fuel additives and common 10% Ethanol fuel but like you said, I think it would have been under a load you noticed it. Anything else done recently not mentioned in your first post?
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    Quote Originally Posted by cruzanrs6 View Post
    Do you know off the top the measuring blocks for the fuel trim (lambda) on the RS6 ?

    Thanks
    001 shows it in the rightmost 2 windows.
    As suggested by Mark, can also try unplugging MAFs. Will make the car run on "limp home" fueling & mostly eliminate up-throttle leaks contribution to the issue. See if that makes it idle okay-ish.

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    Quote Originally Posted by hahnmgh63 View Post
    Gregg, the misfire counter resets after something like 300 or 500 misfires, starts over at zero. I'm following this as it is probably different from my issue. Haven't been able to do any runs on the car with the unusual amount of snow we have gotten. After the car sitting for almost 3yrs it fired up in seconds. Idled great. After a few runs it developed a misfire all cylinders on Bank 2? Shared Plenum so I figure it can't be an intake issue but either fuel or spark. Recently I just started it up and it seemed to have migrated to only cylinder 5? I've now drained the fuel (Almost 3yrs old) and replaced with Ethanol free 93 (Euro about 99~100) Octane. Going to confirm this week if it is spark or an injector.
    Cruzan, with all that said are you sure your intake was seated well? With the MAF's connected electrically and misaligned you will get a miss. You can either re-/seat them and check or just unplug the MAF's and check the misfires. Could you have gotten bad fuel, of course with our general crappy fuel additives and common 10% Ethanol fuel but like you said, I think it would have been under a load you noticed it. Anything else done recently not mentioned in your first post?
    Yes I did verify the intake was seated well, I did wrap one layer of electrical tape around the portion that actually seats in the intake manifold - it seemed to snug up the fit. I am going to do some Vag Com monitoring of the various measuring blocks that you guys suggested. It is just odd that no other errors or codes are showing up. The only thing to add is this condition arose after the following: I was going to lunch with a group about 2 weeks, had 5 people in the car. The car was running for about 10 mins after setting for the morning. I did proceed to "hammer it" to get across a intersection - the car also has a stage one tune (Addict Motorsports). As I came up to a light after the event, it is when the misfiring began.

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    Still a mystery to me. After hammering it I would almost say boost leak from a loose hose but there would be other codes associated like running rich.
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    seems silly but how are your spark plugs? I recently had a misfire (although not everywhere like yours) and new plugs completely solved it. I have no idea why - the old plugs didn't show any unusual wear or coloration from rich/lean running, but it did, and I'm glad!

    back to misfiring...I've always worked backwards to trace the problem - first plugs, then coilpacks, then air leaks. Three things can cause misfires - not enough spark, loss of intake charge boost/overfueling as a result, or spark is ok but air/fuel is boosted to the point where it blows out the spark.
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    Quote Originally Posted by kismetcapitan View Post
    seems silly but how are your spark plugs? I recently had a misfire (although not everywhere like yours) and new plugs completely solved it. I have no idea why - the old plugs didn't show any unusual wear or coloration from rich/lean running, but it did, and I'm glad!

    back to misfiring...I've always worked backwards to trace the problem - first plugs, then coilpacks, then air leaks. Three things can cause misfires - not enough spark, loss of intake charge boost/overfueling as a result, or spark is ok but air/fuel is boosted to the point where it blows out the spark.

    I did replace the plugs. So drove the car and warmed it up came back and did a scan. Fuel Trim Bank 1 and 2 showed up - system too lean. Did some measuring blocks; 001,002,003 091,092,093 (the ones in the 90 at idle and reved up).
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    So as I am looking at the measuring blocks (car running), I smell an odor and notice smoke coming from the drivers side fire wall/engine - could not exactly isolate it. Shut down car and now have another code:16534 Oxygen (Lambda) Sensor B2 S1 P0150 -008 Malfunction in circuit. Restart car - no more smoke still misfiring. Measuring block 2 now has a big difference at idle between Mass Air flow bank 1 vs 2 (5.78g/s : .67 g/s). Also observe the exhaust on drivers side muffler port is much cooler than the passenger side. Gregg is commenting that maybe the 02 sensor wire shorted out.

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    Registered User hahnmgh63's Avatar
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    Too lean sounds like a vacuum leak. Un-metered air getting in past the MAF's. Vacuum line, Intake manifold leak? MAF's for leaks (I know I mentioned this before and you said you checked them but....), O2 sensor could cause one but shouldn't cause both banks to show lean. Vacuum leak can cause both sides as shared plenum. MAF's don't go bad at the same time unless it is a connection/seating problem, O2 should only cause the reading on one bank as it tries to correct the mixture for that banks injectors to match up with the air read from the MAF's.
    Nubcake might be one to know for sure in the tuning, but since it is a shared Plenum, a difference from one MAF to the other for pressure difference from one Turbo or Intercooler leak on one side shouldn't show up in one bank or the other, it should show up in both banks since the Plenum is shared. O2 is reading one side so it affects the fuel injected on one side.
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    Update:
    So I found the drivers side pre cat 02 sensor wiring appears to have shorted (his was on harness mating connector that was replaced some years ago by dealer). Also found some of the small 3mm vacuum lines that were bad off the combi valves and some other. SO all was fixed. I also ohmed out the O2 sensor against a new one and the pass side one and all checked out. Fired up car last night and drove it - no more CEL, running better at idle but still some misfiring. After drive scan said misfire detected on 6,5,4,8. Reset again, fired up another drive scan shows 5, 4 misfire (no CEL). Drove to work this morning, great power under load still slight mis (more so when left in park), when stopped at light/traffic (not really anything). Did another scan at work (still no CEL), shows 5 and 4 BUT also 4 system to lean codes - intermittent and both 02 sensors (Bank 1 and 2) 0 Malfunction in circuit - intermittent. Click image for larger version. 

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    This still looks like vacuum leak (unmetered air). Need to verify how "malfunction in circuit" code is set, but that's likely a byproduct of being too lean.

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