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2.8 V6 rough runner, possible cat?

Discussion in 'A4/S4 forum(B5 Chassis)' started by Jonion, Oct 25, 2012.

  1. Jonion
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    Jonion Member

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    [Oct 25, 2012]
    Well first I'll say hello to anyone who does(or even doesn't) remember me, not been here for ages... but then the Quattro hasn't been running/used for longer than that either lol

    So after sorting out the fuel filter leaking and checking through various other things it still won't run correctly.
    With a boost(battery sits too long) it will start.
    But it idles roughly and is reluctant to rev, then will drop and die if you don't catch it.

    It's as if it's not running on all cylinders but not quite. Yeah I now what a **** explanation.
    Checked all plugs,leads,coils etc and it is getting spark and fuel.
    Oddly this started to happen just after a service, fuel filter change & cleaning of the breather system.

    So today I got the chance to start it up and have grope underneath..
    So the right bank exhaust is getting hot all the way along as you'd expect.
    The left bank isn't as hot. The downpipe is getting pretty warm/hot, the cat is pretty cool, then the rear of the next piece gets warm but I supect this is because it's next to the 2-1 y-joint.

    So I'm thinking the cat is fubarred.
    Any thoughts on this one before I get too far into it?
    Any tips on best methods of removal?

    Unfortunately if it is the cat I've had a stainless exhaust fitted and they welded it to the cat, I can still remove that section but can't simply replace witha standard replacement.



    Hope you didn't all fall asleep reading through that.

    Next step I think is to sell the car on, and take off the nice wheels and sell them seperately..
    unless it redeems itself pretty damn soon, it's been sat for 6 months. :-(

    Cheers.
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  3. Bradderz_1988
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    Bradderz_1988 Dont replace it, Upgrade it !!

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    [Oct 25, 2012]
    Vagcom scan for faults and a throttle body alignment would be first on my list if battery has died !!
    #2
  4. Jonion
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    Jonion Member

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    [Oct 25, 2012]
    Already done that, VagCom has got fed-up of being plugged in just to report 'No faults' lol
    I knew there'd be something I forgot to put in the first post.
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  5. Bradderz_1988
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    Bradderz_1988 Dont replace it, Upgrade it !!

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    [Oct 25, 2012]
    Compression test ???? Lambda readings on both banks ???? Take the lambda out and get some welding rod and see if you can get it down the cat but be gentle incase its still there lol
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  6. C6 DRN
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    C6 DRN living the dream

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    [Oct 25, 2012]
    Might be worth putting "Cataclean" through it see if it makes any difference?
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  7. Jonion
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    Jonion Member

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    [Oct 26, 2012]
    Compression is fine.
    Not got the lambda readings yet, waiting for laptop to charge so I can get out there.
    Need to get VCDS activated again before I can do too much with it though.

    To get enough access to the cat to check it I may as well take it off and do it that way I guess.
    Who decided where to fit the joints on these cars? think they were having a laugh.

    Won't be using cataclean, don't like additives or potential snake oils. And tbh for that to have any effect I'd have to run it for quite a while, not an option when it hardly runs at all. It's also £20 towards the real cure once determined. It isn't drivable by any means.
    #6
  8. Jonion
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    Jonion Member

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    [Mar 6, 2013]
    I'm going to return to this thread rather than start a new one...

    So far checked the cat and it isn't the problem, no matter what I do with the exhaust it runs the same.
    Have checked and got no fault codes at all.
    Checked fuel pump and it seems to be working just fine when tested.

    It runs but appears to be missing on at least a couple of cylinders, maybe a whole bank. Hard to tell.

    Occasionally it will pop/bang from the exhuast as if it's trying to fire on another cyl/s.
    It runs like this whether at idle or if you rev it a bit.


    does anyone have suggestions on where to start using VCDS Lite to get readings that may be relevant? Which measuring blocks mean what etc...?
    Full scan shows no relevant faults, just the rear lock pump running too long.

    My next option is to part this car out if anyone wans tto give it a good home or have the parts from it, I can't have it sat here for too much longer.
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  9. gen.heinz guderian
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    gen.heinz guderian Well-Known Member Regional Rep VCDS Map User

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    [Mar 6, 2013]
    I would suggest using vcds full version ,not lite.
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  10. Jonion
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    Jonion Member

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    [Mar 6, 2013]
    I have the registered (paid for) version of VCDS Lite and if that's not enough I'd rather just scrap the car. It's not worth it to me to spend another £200 on 'possibly' finding the problem.
    TBH Not sure what(if anything) that would offer over what I have now anyway.

    Anyone know what the lambda numbers should be? Or what sensor's are in what measuring blocks?
    Or a link to such thinsg so I can find the info myself.
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  11. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 6, 2013]
    registered version of VCDS Lite is more than enough for a B5.

    No idea what blocks you need, they're engine specific, but the labels should tell you what your looking at?

    Have you removed/inspected the plugs for signs of missfiring?

    Tried unplugging the MAF sensor to rule that out?
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  12. Jonion
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    Jonion Member

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    [Mar 6, 2013]
    Hi aragorn.

    Changed plugs not too long back and checked them again. No signs of a problem with them.

    MAF and a lot of other thinsg unplugged and cleaned up.
    All vacuum hoses that can be reached have been changed but haven't affected the running.

    Here's something that may be a sign of something.
    If I remove a plug lead it affects the running slightly no matter what cyl it is (even though it seems the left bank is the one having the issues).

    Although I've tested the fuel pump for flow removed from the car... is it possible it's a weak pump having problems when under pressure?
    Going along the lines that the first bank running OK is supplied by the fuel rail first, so maybe it's dropping pressure the further along it's route iyswim.
    I'll pull off the return line tomorrow and see what results that gives.

    I'm going to need to get some more straws at this rate.
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  13. Jonion
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    Jonion Member

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    [Mar 7, 2013]
    So fuel delivery checked and working as it should.
    Full flow through return line when up to pressure.

    Now I'm back to checking plug leads. Going to pull all the plugs and check/clean them up again just for the sake of it.
    Might swap the leads around and see if it changes anything.
    Possibly a weak coil or two?

    Any way of checking this with VCDS ?
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  14. Jonion
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    Jonion Member

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    [Mar 8, 2013]
    OK so upon checkig nthe plugs.. I find the Bosch things are not as they should be. Despite only doing a few k miles soem of them have detiorated badly.
    So stuff that and off I went to get some proper NGK plugs. No idea why I agreed to have the Bosch ones in the first place.
    Once fitted and a few other thinshg checked over the car now runs again, has a slight hesitiation after idle but that could be very low fuel level.
    So after all this time I'm still not 100% sure what caused the main problem.
    It has had a fair few bits changed for the better over this time though. Lucky car.

    Tomorrow it will be moved for the first time in 12 months and go straight to a date with the MoT man. Wish it luck.

    Then I can get on to the other little problems, leaking vacuum on the rear lock, leaking rear washer hose in passenger footwell.

    But at least it runs now.
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  15. Jonion
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    Jonion Member

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    [Mar 9, 2013]
    So took it for the short drive to the MoT station expecting all sorts of minor(or major) issues after having it sat still for so long.
    Got the usual square wheel feeling for a while and the autobox had a few indecisions.
    But generally it was far better than I had expected.
    Also passed the MoT without even an advisory. Quite pleased with that, saved me taking it straight to the scrapyard at least.
    Was expecting problems with emissions after the lay-off and fueling problems as well. Passed it with ease.

    Now I just have 2 months to decide whether to keep it, sell it or sell some of the random parts I have that I don't need, such as the 17" Audi wheels.

    At least it lives!:sm4:
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  16. jcb
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    jcb Active Member VCDS Map User

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    [Mar 9, 2013]
    how does it run without the MAF plugged in?

    have you changed the coolant temp sensor?
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  17. Jonion
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    Jonion Member

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    [Mar 9, 2013]
    No ideas about the MAF as I haven't unplugged it since it's been runing almost completely properly.

    Coolant temp sensor was changed same time as the cambelt etc.. maybe 5k miles ago
    #16
  18. Jonion
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    Jonion Member

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    [Mar 10, 2013]
    Damn it... so got a nice little misfire just off idle now.. will have to plug it in and scan it again I suppose.

    Fixed the rear washer leak by plugging the connector back together in the kick panel.
    What sort of idiot decides to put a fluid pipe through a bunch of electrical connectors... and then put a join in it. :wtf:
    I'm surprised that doesn't cause more problems than it seems to.

    Anyone have any ideas on this one?
    The motor in the rear quarter runs for quite a long time when locking/unlocking.
    It hasn't failed to lock/unlock but does throw a code as well. And suggests it's a leak in the vacuum.
    Getting it pinned down to an area/known problem would be very handy.
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  19. jcb
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    jcb Active Member VCDS Map User

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    [Mar 12, 2013]
    have the same in mine. you can identify if it is pressure or vacuum pipe by clamping the pipes at the pump in order and seeing if you get the pump overun
    I gave up looking for mine as it runs half way round the car

    just use the key and deal with the overrun noise
    #18
  20. Jonion
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    Jonion Member

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    [Mar 12, 2013]
    lol, that's exactly what I'll be doing for now.
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