1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

A4 1.8T Running Issues

Discussion in 'A4/S4 forum(B5 Chassis)' started by aragorn, Oct 28, 2011.

  1. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    I've been chasing a weird running issue with my parents 1.8T for a while now. I've tried everything i can possibly think of, but just aint getting to the bottom of it.

    The original problem was really harsh juddering, mostly at low/medium revs with lots of throttle. You could plant the boot at 2500rpm and it would pull, then it would judder harshly (sort of like someone was turning the engine off momentarily)

    I changed the Coils and ICM for spares, and it got slightly worse. I swapped my spare MAF in, and it stayed the same. I changed the plugs and it got marginally better.

    Then i discovered a split hose on the inlet manifold, running to the PCV gubbins, ie a huge boost leak. Repaired that, and the cars much better.

    However its still not right. At random it still judders. Much less frequently and much more randomly, but still happens. Also now, if you give it full throttle in fourth gear say, you can feel constant very slight hesitation. It doesnt just smoothly climb thru the revs, theres constant small judders, somtimes so slight it just feels like a slight reduction in power output momentarily.

    I'm going to swap the coils with the ones off my own car, as i know for sure they're good, and i'm going to refit the original MAF sensor incase the one i've fitted is slightly dodgy and was masked by the boost leak.

    Any other ideas?
    #1
  2. Foxmeister
    Offline

    Foxmeister Fired Up!

    Joined:
    Apr 1, 2009
    Messages:
    1,779
    Likes Received:
    4
    Pretty much as you've said, swap the components back that you did initially incase these 2nd hand units may be faulty, then take it from there. How are HT leads etc?
    #2
  3. Brendan12
    Offline

    Brendan12 Member

    Joined:
    May 13, 2011
    Messages:
    142
    Likes Received:
    3
    Tired swapping the N75 valve?
    #3
  4. Bradderz_1988
    Offline

    Bradderz_1988 Dont replace it, Upgrade it !!

    Joined:
    Aug 19, 2010
    Messages:
    3,161
    Likes Received:
    100
    Seems like youve checked/replaced the obvious components.

    Fpr, injectors or throttle body maybe ??

    I no when I had a judder one of the coils was shot which developed to a missfire at idle.
    #4
  5. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    It doesnt have HT leads, individual coils on a 1.8T.

    I have a spare set of injectors and a spare FPR at home. Maybe i should send the injectors to be cleaned and then swap them in to rule that out.

    I've not touched the N75, but i did wonder about unplugging it and seeing if the oddness remained or if it went away. Unfortunately it doesnt actually help, because an ignition issue is going to improve with less boost, as might a MAF issue (less airflow) etc. So you might end up thinking its the N75 and swapping it out for no reason!
    #5
  6. adamss24
    Offline

    adamss24 Well-Known Member

    Joined:
    Jul 3, 2007
    Messages:
    3,313
    Likes Received:
    171
    How's the fuel filter ?
    #6
  7. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    203000miles old :p
    #7
  8. NineNails
    Offline

    NineNails Proud sponsor of the snack food industry

    Joined:
    Sep 18, 2006
    Messages:
    583
    Likes Received:
    3
    Was the ICM a good spare? Dunno what sort of advice you were looking for really Kev coz if you don't know what's up with it I doubt anyone else will! and there was me thinking you know everything about these motors lol
    #8
  9. Broken Byzan
    Offline

    Broken Byzan Photographic Moderator Staff Member Moderator

    Joined:
    Apr 26, 2004
    Messages:
    12,568
    Likes Received:
    267
    :banghead:
    #9
  10. gen.heinz guderian
    Offline

    gen.heinz guderian Well-Known Member Regional Rep

    Joined:
    Jun 24, 2011
    Messages:
    1,359
    Likes Received:
    125
    could be fuel filter , i had a vr6 that wouldn`t rev and turned out filter was blocked.
    #10
  11. macpdm
    Offline

    macpdm Member

    Joined:
    Jul 21, 2011
    Messages:
    410
    Likes Received:
    3
    I have been having all sorts of running issues myself until we plaved around with the DV by manually pushing the plunger in and out and cleaning it we also cleaned the throttle body.So far touch wood its been a week and still running fine.

    Admittedly the symptons I was having was loss of power where it felt like I was loosing boost.
    #11
  12. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    I dont think its fuel related, because if you use the full RPM band its fine. EG if you rev it right out to the limiter, it pulls mostly fine. The juddering all seems to happen around the middle of the rev range, ie peak cylinder pressure/peak torque. Today, third gear 30mph, full throttle, it started to accellerate then BRRRRRRR juddering and complete loss of power.

    I tried refitting the other maf today, no change.

    I'm going to take the four known good coils from my car and fit them to it tomorrow. Might as well throw the ICM in as well. That way i know every ignition component from the spark plugs back is perfect.

    Assuming its not the coils, my thaughts at the moment are:

    Another Boost leak - I've looked as best i can, but maybe theres something else lurking away somewhere. Really need a pressure tester to diagnose this properly and i dont have a compressor to hand.
    Faulty MAF - I have two, and swapping between them doesnt really seem to change the symptoms, but i guess they both could be faulty as they are both 14 years old.
    Fuel Delivery (Pump/filter/injectors) - Seems sort of unlikely as it does pull thru the dodgyness and seems to deliver full power.
    Faulty coil wiring - long shot, if it was faulty why would it only cause problems at peak load. Unless it was a grounding issue and the coils are being starved of power...
    Faulty ECU or Harness - getting to be a serious long shot as to why it could cause missfires at the very odd times that it does.
    #12
  13. Bradderz_1988
    Offline

    Bradderz_1988 Dont replace it, Upgrade it !!

    Joined:
    Aug 19, 2010
    Messages:
    3,161
    Likes Received:
    100
    That sounds exactly like what mine was doing after the FT install as the car was running hardly no boost before then when it was back to peaking 12-14psi it would knock one coil out during boosting but like I said That was shortly noticed at at idle.

    Have you had the plugs out to check there no signs of arcing up the sides of the plugs ??
    #13
  14. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    Brand new plugs went in on Thursday. No change.

    It drives perfect if you dont load it up. Idle is smooth. Just passed its MOT so i presume emissions are spot on.

    Maybe theres a dodgy coil in both sets of four...
    #14
  15. Foxmeister
    Offline

    Foxmeister Fired Up!

    Joined:
    Apr 1, 2009
    Messages:
    1,779
    Likes Received:
    4
    Had a similar miss on a Cosworth years ago, only noticible in certain gears under mid to heavyish acceleration, turned out to be the crank sensor going.

    Sounds more electrical than fuelling etc.
    #15
  16. IN 2 Deep
    Offline

    IN 2 Deep Hoonigan

    Joined:
    Oct 13, 2009
    Messages:
    380
    Likes Received:
    5
    Check the coil pack wires, they tend to get a tad brittle over the years and can cause the most annoying intermittent faults, have you checked the TPS is reading ok? Sounds to me like a wiring issue over a sensor issue. If you've ever taken a loom apart you will know that all the grounds, postives etc are all commoned together under a mile of tape on the ecu plug end, that to me is a ball ache waiting to happen. Sounds like one of those issues that's gonna test your metal :thumbsup:
    #16
  17. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    299
    Well its fixed.

    I fitted two of the original coils to my car and drove it around for a day with no issues, so i now had 6 coils i knew for sure was good.

    So i then took four of those 6 and swapped them in.

    Fitted two of the removed coils to my car and now both cars are working fine. i did it that way so if my car then started exhibiting the symptoms it could only be one of two coils.


    Having talked it over with dad, we recon one of the replacement coils was faulty, but the original problem was caused by the boost leak. He says the car got distinctly worse when i changed the coils. So the original juddering has been the leak. I've fitted a dodgy coil when trying to fix it, then later fixed the leak, leaving only the faulty coil!
    #17

Share This Page