N75 vac test

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by meetooo48, Jan 12, 2012.

  1. meetooo48

    meetooo48 New Member

    Joined:
    Dec 28, 2011
    Messages:
    13
    Car:
    2001 jetta tdi
    Hi all:
    What is the max vacuum pressure out of the N75 to the vnt actuator. I am assuming that it should increase as the engine is reved?
    login to remove this ad
  2. Keith_J

    Keith_J New Member

    Joined:
    Jan 2, 2012
    Messages:
    30
    Car:
    2k Jetta TDI
    No, it isn't speed controlled. Rather, the ECU varies the duty cycle to N75 to regulate the charge pressure (boost) according to the requested power, smoke map, NOx limitation etc. It is considerably higher pressure than the absolute vacuum attained by the vacuum pump.
  3. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    22,048
    Car:
    2006 Jetta TDI
    Location:
    CT
    If you're not seeing vac you could have a leak somewhere, the metal thing that comes out of vac pump has been known to leak, and of course check all hoses.
  4. meetooo48

    meetooo48 New Member

    Joined:
    Dec 28, 2011
    Messages:
    13
    Car:
    2001 jetta tdi
    If I remember correctly when I put the vaccum guage on the hose to the VNT it showed a constant 20 HG vac, even when reving the engine. That sound right?
  5. Frank M

    Frank M Member

    Joined:
    Aug 15, 2011
    Messages:
    201
    Car:
    2000 NB
    Mods:
    ventectomy

    My original N75 with 290,000 miles on it would barely got over 15.
    I replaced it and the new one gave me close to 20.
    These readings were taken at idle.
    I had a solid 22 going into the valve.
    Obviously the 20 gave me quick pedal response and more power throughout the rpm range.:bowdown
    I assume they wear out and leak internally.
  6. mdt

    mdt New Member

    Joined:
    Feb 16, 2012
    Messages:
    4
    Car:
    jetta / 03
    I belie if you can T your Mighty Vac between your N75 and your actuator with a long hose, the vacuum should drop down to 5 Hg pretty quick if your accelerating because the boost builds quickly if there's no leaks

Share This Page