VW TDI forum, Audi, Porsche, and Chevy Cruze Diesel forum banner

1 - 20 of 20 Posts

·
Premium Member
Joined
·
74 Posts
Discussion Starter #1
I have a 2003 VW Jetta TDI with the Unitronic Stage 2 chip software, DG race pipe and EGR delete. Soon I plan to upgrade my clutch using a single mass flywheel and PP520 nozzles. I'm convinced from the TDI Club TDIFAQ that I should have a turbo boost gauge, which I ordered today, and that I must adjust the VNT linkage on the turbo to lower the boost pressure.

The TDIFAQ also states that the VNT linkage is located above the diaphragm housing on the turbo. So where exactly is that on the turbo?

I've tried searching for a picture, but was unsuccessful, and my Bentley manual was really no help. Does anyone have a picture of the VNT linkage that needs to be adjusted or a step-by-step procedure?

Any help would be great!
 

·
Super Moderator
Joined
·
23,902 Posts
I don't have any pics, but it's analogous to a "Wastegate rod". Some are adjustable, some are not. Yours should be.

Basically, there's a lever and the rod sticking out of the vacuum can. The rod should have threads on it, just loosen a bolt and turn the threads and this adjusts the rod length.

Why do you want to adjust the boost pressure, your chip program should regulate the boost pressure.

Also, a boost gauge is pretty much always a big help on any turbo car. The best gauges also have a peak hold function where it records the peak value reached. This lets you see spikes too fast to see.
 

·
Premium Member
Joined
·
59 Posts
Here is a pic , IMO, the boost gauge won't be as effective as a Ross tech Vag-Com. You can datalog requested boost vs. actual boost to check if the actuator is adjusted properly. Of course, there could be a boost leak or faulty component that can screw with the datalog but a boost gauge will move too fast for you to accurately track all the readings, rpm, etc., while doing a road test. Recording these values and then sitting down when your not moving is the best way to check it!

 

·
Premium Member
Joined
·
74 Posts
Discussion Starter #4
Thanks for the advice. I have the VCDS (formally VAG-COM), so I'll check into this first. And, today I ordered a turbo boost gauge.
 

·
Premium Member
Joined
·
482 Posts
Why do you want to adjust the boost pressure, your chip program should regulate the boost pressure.

Also, a boost gauge is pretty much always a big help on any turbo car. The best gauges also have a peak hold function where it records the peak value reached. This lets you see spikes too fast to see.
2nd on both points, the chip should control the boost. Some people add a boost valve to control spiking or fix a problem but check it with your gauge, it should be fine. The reason why a boost gauge isn't on every car is because customer A says "how come customer B's car makes more boost?". It depends, two identical cars will just make different levels of power. Same thing with the water temperature gauge or oil pressure gauge.
 

·
Premium Member
Joined
·
482 Posts
so what's the point of a boost gauge if vag com is so much better?
Because your vag com isn't plugged in all the time. A boost gauge is. You wouldn't want to drive around with a laptop in the passenger seat, it wouldn't last very long before breaking.
 

·
Premium Member
Joined
·
74 Posts
Discussion Starter #9
Last night I fired up my Ross-Tech VCDS to check the turbo boost, and I used the instructions provided by R-T. Basically, in 4th gear on the highway I gave my Jetta TDI full throttle from around 1500 rpm to 3500 rpm. Below are three of my five runs. Run 2 occurred on a decline and Runs 3 & 4 occurred on a slight incline (fairly level). According to the R-T instructions, I should see a spike at 2100 mbar that is then quickly regulated at 1900 mbar through the whole rpm range. Of course, I don't see that.

So how do I interpret my data? Does it indicate that I definitely need to adjust my turbo's VNT linkage out? Is there something else about my turbo that I should be concerned about? Since my experience with my TDI is only 6 months, I wouldn't mind a little feedback.





 

·
Premium Member
Joined
·
482 Posts
Small spikes aren't bad but larger ones aren't optimal. The first graph is fine, the 2nd and 3rd are not horrible but are still bad. Try 1 turn longer on the actuator and see what happens. Are you stomping on it only low in the RPM range? It should be more stable if you are at low load, medium RPM and then stomp on it instead of stomping on it at low RPM.
 

·
Registered
Joined
·
3 Posts
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?
 

·
Super Moderator
Joined
·
23,902 Posts
It's possible but do more tests to confirm.

Remove the vacuum line at the N75 valve (so you don't have to get under the car) and draw vacuum, release, and repeat. If it doesn't hold vacuum then the problem is the vac line or actuator.

Then separate the rod from the lever and move each separately. If the lever is sticky then the problem is sticky vanes inside the turbo as described in the article.
 

·
Registered
Joined
·
3 Posts
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.
 

·
Super Moderator
Joined
·
23,902 Posts
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.
I don't see an image, read this post http://www.myturbodiesel.com/forum/showthread.php?t=1044 if you are having problems posting an image.

Sounds like the actuator is working but disconnect the actuator's rod from the turbo VNT lever. http://www.myturbodiesel.com/1000q_how_to/a4/VNTturboclean.htm Read this, you may be getting sticky vanes. Do some hard hot runs to see if you can cook the turbo and burn out the buildup, if not then it has to be removed and manually cleaned.
 

·
Registered
Joined
·
3 Posts
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.
 

·
Premium Member
Joined
·
118 Posts
I don't see anything when you cut/paste the link, it gets shortened. Try the cut/paste the full URL of the picture and that should work
 

·
Premium Member
Joined
·
1 Posts
Here is a pic , IMO, the boost gauge won't be as effective as a Ross tech Vag-Com. You can datalog requested boost vs. actual boost to check if the actuator is adjusted properly. Of course, there could be a boost leak or faulty component that can screw with the datalog but a boost gauge will move too fast for you to accurately track all the readings, rpm, etc., while doing a road test. Recording these values and then sitting down when your not moving is the best way to check it!

which way for more boost ?
 
1 - 20 of 20 Posts
Top