Alh - overboost!!!????

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by rhader, Jan 6, 2011.

  1. rhader

    rhader New Member

    Joined:
    Jan 6, 2011
    Messages:
    3
    Car:
    2001 Jetta ALH, 2003 Golf ALH, 1975 Westy 1Z
    Over Boost Condition - 2001 Jetta TDI automatic

    Have the following error code:

    1 Fault Found:
    16618 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
    P0234 - 35-10 - - - Intermittent
    Readiness: 1 1 0 0 0


    I havent yet gone back through the Limp Mode thread but figured I would throw this out there for some critic.

    Where should I start with this one?

    Too add a bit of background to this - I just replaced the lifters on the head and just finshed setting the timing and everything is running well. lots of power from start - engine starts up fine and timing is within spec - slightly advanced as I set it as such using Vag Com as the diagnostic. and set the timing using the 3 IP bolts...

    Also a New to me /good working used turbo that had no play and the actuator was almost brand new was installed.

    Cleared all of the previous codes and first day I drove it to ensure all bugs had been sorted out etc.. and runs fine - gets up to speed - shifts well (for an automatic) but still seemed to be somewhat lacking and doesnt accelerate like my 03 Golf 5spd does... I had chalked that up to the auto as it reall was pretty close. Until the CEL light came on!

    so afte that sat with me for the rest of the day... When I got home first thing I checked obviously and the above error code was displayed...

    So what could be causing the 'Over Boost' condition?

    I have done the Vag Com EGR mod to turn off teh EGR to 'offroad use' condition... and the vacuum line to the EGR is a little wonky - I have made a home edition of the WD40 nylon insert mod to correct this but its possible that it isnt sealing fully... what error codes would this produce?
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  2. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    21,931
    Car:
    2006 Jetta TDI
    Location:
    CT
    than it's probably not related to the lifters and timing belt. Vacuum lines could have been disturbed. I would not do the vag com mod to turn off the EGR - this is in the FAQ on another site but it's since been found that many people say it lowers mpg because the ECU will self adapt to low flow. The only way to turn the EGR completely off is with a block off plate or removal and chip tuning. You could use a restrictor plate like a gasket with a small hole in it w/stock adaptation but according to Oilhammer it still throws a CEL once or twice a year. Not a problem since you have vag com.

    I don't think the EGR produced the overboost since overboost is normally vac lines to turbo, n75 solenoid, actuator, or sticking vanes. Though maybe it resulted in a vac line leak which caused the turbo control line to not function correctly. This is just a guess, off the top of my head not sure how a leak at the EGR line would affect the N75 line.

    Another thing- was the actuator adjusted at all when installed? Checked rod position against old one? Checked w/vacuum gauge tester? If not, that would be the next thing I would look at.
  3. rhader

    rhader New Member

    Joined:
    Jan 6, 2011
    Messages:
    3
    Car:
    2001 Jetta ALH, 2003 Golf ALH, 1975 Westy 1Z
    another thought - is there different travel lengths between the actuator rod travel on automatic vs. a 5spd?

    IF so - could that potentially cause an 'OVERBOOST' condition? i.e. holding the vane actuator open longer than expected.... what would be the best correction for this?

    i.e. IF this is the case - can I program the difference using VCDS? OR would it be better to adjust the travel on the actuator arm?

    the actuator as well as the turbo itself was fairly new - the yellow paint from the factory was still on the actuator arm so I didnt adjust it - I compared it with the old one and it seemed similar - though the old one had barely any travel at all which was another problem...

    any particular method to set this length for fully closed and fully opened?
  4. pdq

    pdq New Member

    Joined:
    Dec 26, 2010
    Messages:
    37
    Car:
    Audi S6 Avant 1995.5
    Mods:
    chip, RS cams and exhaust
    Theoretically vacuum leak at the EGR, especially on the supply side could cause the vane actuator to misbehave. A quick check with a Mityvac will find that though if you check for leakage on the supply side.

    Vag-com in graph mode monitoring measuring block 11 is the best tool I know of for boost diagnosis.
  5. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    21,931
    Car:
    2006 Jetta TDI
    Location:
    CT
    Not that I'm aware of.

    If it's properly adjust it's best to not touch it but that assumes it's correct. Here is how: http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm and more on how it works. Can't program it with VCDS since it's a physical adjustment.

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