04 jetta turbo actuator vacuum readings while driving

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by Jim Wild, May 9, 2017.

  1. Jim Wild

    Jim Wild New Member

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    Car:
    VW, Jetta wagon tdi, 2004
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    Good afternoon. I have a turbo issue. It is an 04 jetta bew tdi. I replaced the original actuator a few years ago due to the original rusted. I think I replaced the N75 valve also because rust got sucked up into it. All was good for a while but then started going into limp mode. Shut it off and restart, it resets and is fine for maybe 3-10+ miles then goes into limp mode. Code is rod sensor not correct reading and under boost I think. I am pretty sure the rod is adjusted correctly because it worked good for maybe a year. I hooked my mightyvac to the actuator and it seem to operate the lever correctly. On my gauge I get around 20inHg to bottom the arm movement. I vacuum tested the hose from the N75 to the actuator and that didn't have any leak. I have T'd into that line and hooked my mightvac to it. So now my question is, what should be the typical readings be at idle, load and any other check points. Mine results seem to really vary. When I first started it, it went up to 20 and stayed there. Under load it would drop to maybe 15. Then when it hit limp mode, 0 vacuum. So shut it off restart, then vacuum at idle was around 7-10"Hg. under load up to 15 or so. I took it 5 miles or so to get fuel and while coasting down the hill the vacuum popped up to 20". after fueling, start up vacuum at 7-10. From what I have read, seems like as the load is increased the vacuum to the actuator should also, and so at idle it should be pretty low vacuum amount needed.

    I also unplugged the connection at the actuator and plugged it back in, in case it was a bad connection but didn't affect it.

    Is the N75 bad causing inconsistent vacuum?

    Thanks for any help
     
    Last edited: May 10, 2017
  2. chittychittybangbang

    chittychittybangbang Administrator

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    It's possible. The vac in 1st conditions sounds good. At idle, should have higher vac than under load, unlike your 2nd test. Also check for leaks in vac lines.
     
  3. Jim Wild

    Jim Wild New Member

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    So at idle and coasting with no load, vacuum should be 18-20. Under load, vacuum will be less. The actuator rod should be pushed in at idle and extended for load. What about high RPM at cruising or slight load? Thank you
     
  4. crsmp5

    crsmp5 Well-Known Member

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    this is where the basic vnt settings via mityvac is needed known... the vac gauge is that same thing ;wink wink; so full vac is fully small... 0 vac is biggest, so the middle is the vnt function...think ita 18 on high side and 4 on low.. but gotta look it up..

    then with your boost gauge watching the 2, boost and vnt vacuum you will see where the vnt vanes stick/hang-up/spikes to get limp.. if you do not see a surge/mess up then it would be in the n75/lines a blocked fresh air line of the filter will screw it up

    mess up.... you will see the vnt system work but still building boost, boost should fall off.. semi sticky vanes will be very quick.. like someone other then driver needs to watch them.. but that spike is all it takes..

    the 2 are a nice distraction to driving.. but id perm install them both along with a egt gauge cause then you know everything thats going on with the turbo and what controls it.
     
    Last edited by a moderator: May 11, 2017
  5. Jim Wild

    Jim Wild New Member

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    I don't have a boost gauge on it. And I have the mityvac rip tired to the wiper. LOL. I'll have to drive it around more and watch vacuum. So always should be around 20 at idle and less at load.
     
    Last edited by a moderator: May 11, 2017
  6. Jim Wild

    Jim Wild New Member

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    I should probably check the vacuum coming right off the vacuum pump. I am not to familiar with the item location under the hood. Anyone have a link or picture that shows where the vacuum pump is and where would be a good place to test the vacuum off it?
     
  7. crsmp5

    crsmp5 Well-Known Member

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    well.. till you can see if turbo making boost or dropping boost as the vnt works.. you only have some info.. but not enough to do anything usefull
     
  8. Jim Wild

    Jim Wild New Member

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    I have a used boost gauge but I need the fitting that goes into the pipe. Anyone know where I can get another one?
     
  9. crsmp5

    crsmp5 Well-Known Member

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    i use the local ace hardware to buy brass fittings...
     
  10. Jim Wild

    Jim Wild New Member

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    My local auto parts store sold me an oil pressure gauge kit. And a threaded union that I was going to probably tap and thread it into the intercooler pipe.

    Best place to install the end is in the upper plastic pipe?
     
  11. Tom MacDonald

    Tom MacDonald Member

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  12. Jim Wild

    Jim Wild New Member

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    So, I finally got the boost gauge hooked up along with the vacuum. Took it on a short drive to the convenience store last night, 8-10 miles round trip. Vacuum seems strange. What is the max boost for a stock tdi? When I first start the car, vac goes to 20. Seems to become more variable as it warms up. I think I saw around 25psi for max boost. More boost, less vac which seems in general ok. Just coasting or cruising at no real load at 60mph, the vac would only go to 10 maybe. Should the vac be closer to 20 in light to no load with no boost needed? Stomp on it and the vac would increase to like 15 and then decrease as boost increased. Started it to leave the store and vac only got to 10. Pulled a small incline with maybe 10psi boost, vac around 10, then vac dropped to nothing and limp mode. shut it off, start up and vac goes to 20 and the remaining 4 miles home, up a 3/4mile long incline held boost and didn't go into limp mode. I need to do more driving and better note taking to better characterize vitals when things happen.
     
  13. crsmp5

    crsmp5 Well-Known Member

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    where it went to limp.. killing all vac... need to see if over boost or underboost code... if no vac vnt should be maxed out causing a underboost... if it says over boost.. the vanes stuck inside turbo then spiked hitting limp.. takes a 2nd driver to watch as it spikes for a very quick moment..

    next you asked bout vac reading.. it should be max when no boost.. else that vac is like a water spout... higher number smaller turbo... smaller number big turbo.. so to run mid range.. vac should be mid range...
     

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