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

Flat spot - to EGR, or not to EGR...

Discussion in 'A4/S4 forum(B5 Chassis)' started by evilscotsman, Sep 6, 2010.

  1. evilscotsman
    Offline

    evilscotsman Space Cowboy

    Joined:
    May 1, 2008
    Messages:
    1,350
    Likes Received:
    1
    Well, now that my sensors are all good, and no fault codes exist, I am finally driving the car with all its faculties in tact.....which I now find has a flat spot.

    Its bang on 2000 rpm, and most noticable when accelerating lightly, its like theres a dead band on the throttle. (AFN TDi) I think its caused by the egr valve letting exhaust gas bypass the turbo, but does anyone know if the egr on the AFN engine is open with atmosphere and closed on vacuum or vice versa? I am trying to figure out its rest position when there is no vac, passing gas or shut?

    Since my egr originally had a dud plug connected to it, and the actual egr plug was on the imts (IAT) then the car had no egr control. Since putting the plugs right, the engine is soooooooooo quiet its like a petrol motor now except at idle, and even then its very subdued.

    It pulls fine, but there is a noticable jump after 2k which was not there before, its like the first 1/4 to 1/3 of throttle does nothing, but push it down more and theres a sudden rush of acceleration. It used to pull smartly from 1500, now it starts pulling ok there, but goes limp for a second at 2k, then continues pulling again, very very annoying as I use from tickover to 3k max, relying on the low down torque.

    I am thinking of disableing the vac line to the egr so it doesnt work but without throwing a code, but does anyone else have any negative aspects of knocking the egr out? I know it needs to be working for the mot or it will likely fail NOx readings, but has anyone else got the same results as me when its connected, and did disconnecting it fix the problem, or am i barking up the wrong tree?
    #1
  2. jcb
    Offline

    jcb Active Member

    Joined:
    Sep 19, 2005
    Messages:
    4,118
    Likes Received:
    0
    can you monitor the EGR block on VAGcom?
    #2
  3. evilscotsman
    Offline

    evilscotsman Space Cowboy

    Joined:
    May 1, 2008
    Messages:
    1,350
    Likes Received:
    1
    nah, my vag lead is fooked and my autech vag405 handheld can read and reset codes on any vag module but cant see individual measuring blocks. I guess im gonna have to buy another lead. Cheap now tho.

    I plugged the egr valve vac pipe, and it ran fine all the way home this morning, but after about 20 miles, I got limp mode, no cel, no boost, no power, so I stopped and scanned it and got "manifold pressure - control difference - static" - turned off, reconnected the egr and cleared it (not sure that the egr vac pipe blocking was to blame plus I dont know if boost error was too high or too low) but I suspect the egr isnt shut properly, will have to look tonight at work.

    I think whats wrong with the egr when connected, is it moves sluggishly, tested by pulling the pipe off when running and touching it to the stub on the valve, it doesnt snap open and shut, but slides lazily. I will take it off, make sure its clean and closed, then try the delete again. It ran fine with the egr solenoid plug on the imts, so plugging the vac pipe shouldnt bother it. Also suspecting the vnt actuator at this point.

    I think the car was driven for a good few hundred miles with no egr and no vnt movement since it was stuck in limp mode from a blown ecu fuse when i bought it.
    Last edited: Sep 6, 2010
    #3
  4. aragorn
    Offline

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

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    12
    The bigger issue, is that if the valves sticking open, even if its supposed to be closed with the vac line off it might not be.

    You wont need it for the MOT. Mot only checks smoke emissions, and the lack of EGR makes the engine burn cleaner, so less smoke.

    I'd look at removing the valve and fitting a blanking plate.
    #4
  5. aragorn
    Offline

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

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    12
    While your in there, check ALL the vacuum pipes and hoses for splits or leaks.

    You may well find its the turbo vanes though, and that would also account for the fault code.
    #5
  6. evilscotsman
    Offline

    evilscotsman Space Cowboy

    Joined:
    May 1, 2008
    Messages:
    1,350
    Likes Received:
    1
    yeah sounds like a plan Aragorn, im thinking the egr is not closed properly too. The vnt actuator may have caused the boost error but im just guessing, i tried moving it the other day by hand, it didnt move far either way and is creaky / squeaky - is this normal?

    The other day, after fixing the sensor plugs, both the egr and the vnt would have moved for the first time in many months, the guy was using the car like that till I bought it.
    #6
  7. aragorn
    Offline

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

    Joined:
    Jan 30, 2008
    Messages:
    15,495
    Likes Received:
    12
    creaky/squeaky moving parts are rarely normal :p
    #7
  8. evilscotsman
    Offline

    evilscotsman Space Cowboy

    Joined:
    May 1, 2008
    Messages:
    1,350
    Likes Received:
    1
    yah I just thought since the vanes get a bit of punishment from soot and heat, they may be creaky anyway. Is the turbo easy to take off and clean or is there a better way to clean it without removing? Im planning to take the inlet off and clean it anyway.

    EDIT - found this excellent tdi site: How to test and replace VNT turbo actuator VW TDI
    Last edited: Sep 6, 2010
    #8

Share This Page