[hbbowman]

I'm having an issue with the boost on my 2003 TDI. I replaced the actuator over a year ago. In doing so, the old VNT linkage was not removed intack. So, with the new actuator, I had to manually adjust the length to get the boost on as soon as possible without putting the car in limp mode.

So recently, my TDI started delaying power until about 3000 rpms. I decided to readjust the VNT linkage as this was a problem when I first installed the actuator. I also checked the web and found the article: http://www.myturbodiesel.com/1000q_how_to/a4/VNTadjust.htm. I wish I had found this originally!

So, I adjusted the VNT linkage to get the boost on sooner (i.e. I shorten the length of the rod). Now when I check via VCDS -> "engine", "measuring blocks", group 11 and graph, I have a problem. When I start off at a slow speed (low rpm) in 3rd gear and floor it, the actual boost has a long lag until 2000 rpm. The boost then significantly over shoots the requested boost from ~2400 rpm to 4000 rpm. (http://i149.photobucket.com/albums/s54/hbbowman/vwData.jpg)

If I shorten the VNT linkage, I can reduce the lag. But, this can also cause limp mode. If I lengthen the VNT, the overboost is reduced. But, the lag in boost is even worse.

Is it possible the N75 is not functioning correctly?

I think my issue my be due to the new actuator I put in last year. I did used one of the not recommended copycat part sellers listed in the article (http://www.myturbodiesel.com/1000q_how_to/a4/VNTadjust.htm). I was trying to save a few bucks. Would replacing the actuator with a true VW part (VW# 038 198 716) resolve the lag time in boost and over boost?

 

[hbbowman]

I did that, it holds vacuum. The actuator starts to move near 5 to 6 inMg (i.e. near were it is suppose to). And fully down at 20".

I added an image from the VCDS so you can see the lag followed by overboost. I'll swap the N75 with the EGR and run the VCDS test again. If that is the same, I think I'll get the VW part for the actuator.

 

[hbbowman]

I think the turbo VNT lever is okay (http://i149.photobucket.com/albums/s...man/vwData.jpg). I'm getting boost, just delayed and then over boost. How does a stuck vanes turbo respond? I don't think mine is just sticky, because I drive on the hard side and it has never acted like it is getting cooked.

When I installed the new acutator last year, the lever manually moved fine. I've owned the car for almost 2 yrs, so I really don't think it is stuck.

Also, I switched the N75 and EGR, but no change. I think the cheap acutator I have has too little working range. It is late to open, then goes to far. I don't think the acutator can hold the vanes at a middle position.