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

1.9 tdi AHU engine... replace the map sensor OR n75??

Discussion in 'Diesel forum' started by oldbanger, May 16, 2013.

  1. oldbanger
    Offline

    oldbanger New Member

    Joined:
    Oct 5, 2012
    Messages:
    26
    Likes Received:
    0
    hi all. my car is running slow after it warms up. no boost after 10 minutes or so . I have ran vcds and im getting ' 17958 -boost control deviation'.

    from what I have read on other posts, usually it will say positive or negative deviation, as in too much or not enough boost.

    I have got a price on both map sensor and n75 and they are both roughly £60. but they will not take any returns.

    so my question is - should I go for the n75 or could it just be the map sensor? I got a feeling its the sensor rather than the valve, as it only ever says deviation, not negative or positive deviation.

    Please advise .
    #1
  2. adamss24
    Offline

    adamss24 Well-Known Member

    Joined:
    Jul 3, 2007
    Messages:
    3,329
    Likes Received:
    171
    What year is the car ? Early AHU had a MSA15 ecu on which the MAP sensor is built into the ECU, later EDC15 had an external MAP sensor. Look at the engine, the MAP sensor is fitted on the hard, black plastic pipe which goes to the inlet manifold from the intercooler...
    #2
  3. oldbanger
    Offline

    oldbanger New Member

    Joined:
    Oct 5, 2012
    Messages:
    26
    Likes Received:
    0
    Thanks for the quick reply. yes the map sensor is on the plastic inlet manifold pipe. I even took it out and looked at it's prongs. no oil etc, very clean. this is an a4 july 99
    #3
  4. adamss24
    Offline

    adamss24 Well-Known Member

    Joined:
    Jul 3, 2007
    Messages:
    3,329
    Likes Received:
    171
    Can you see the requested boost vs metered boost when you plug in vcds ? I would look for loose vacuum pipes, replace the MAF and check if the N75 works... The wastegate actuator is known to seize so have someone rev the engine for you whilst squeezing the boost hoses, if no boost then the penny valve/wastegate valve has gone walkabouts !
    #4
  5. oldbanger
    Offline

    oldbanger New Member

    Joined:
    Oct 5, 2012
    Messages:
    26
    Likes Received:
    0
    Ive only got the free version. don't think you can monitor that can you (with free version)?
    the maf is fine. the turbo boosts fine until after about 10 minutes, petfectly normal speed ann acceleration. I have also checked the vacuum hoses, even replaced the 1 which is at quite a sharp angle. ive checked the actuator rod. it moves correctly. so im thinking the actual wastegate is fine. ive really tinkered about for a while before starting this thread. im % 99 sure it's either the map sensor or the boost control valve (n75). its just I know that with my luck i'd buy the n75 and then it would end up being the map sensor which was actually needed or vice versa! if you were to take the gamble would you buy the n75 or the map sensor?
    #5
  6. oldbanger
    Offline

    oldbanger New Member

    Joined:
    Oct 5, 2012
    Messages:
    26
    Likes Received:
    0
    well... I fittied a brand new boost control valve and no joy!
    #6
  7. adamss24
    Offline

    adamss24 Well-Known Member

    Joined:
    Jul 3, 2007
    Messages:
    3,329
    Likes Received:
    171
    With cars troubleshooting electrical faults i would always start with the cheaper part first !
    #7

Share This Page