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Discussion Starter #1
I'm new to this forum, but a long time devoted TDI fan. I have a 01 Jetta TDI with a VNT-17 turbo. I worked great for some time with all my mods, but now I am having over boosting issue. It over boosts easily between 1800 and 2500 RPMs with minimal throttle. Causing severe surge. I put a guage on the actuator and it begins to move with less than 1/2 of mercury. I read that it should move till at least 3-1/2. Does anyone know if that is causing my over boosting issues? It is just that my actuator is bad and needs to be replaced? the actuator does hold under vacume showing no signs of leaks. If anyone could give me there imput I would greatly appreciate it
 

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Try adjusting the rod to make a mechanical adjustment:
http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm

or adjusting the chip tune. Chip tune controls how the N75 solenoid controls boost by controlling vacuum to the VNT actuator. You could take some logs and send them to your tuner to have them inspect it after making sure the VNT actuator is properly adjusted. If it was installed without checking it, it's possible it has been misadjusted. Not sure why it worked before and now it's not.
 

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Discussion Starter #3
Try adjusting the rod to make a mechanical adjustment:
http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm

or adjusting the chip tune. Chip tune controls how the N75 solenoid controls boost by controlling vacuum to the VNT actuator. You could take some logs and send them to your tuner to have them inspect it after making sure the VNT actuator is properly adjusted. If it was installed without checking it, it's possible it has been misadjusted. Not sure why it worked before and now it's not.
which way would i adjust it, tighten it or loosen it to provent it from opening so easily under low vacume. Becuase it operates with vacume presure and doesn't show any signs of leaking mean that it does work properly. like I stated before, putting the line directly to a vacume guage, it starts to open under less than a 1/2 of mercury. I thought I read it should start to move till about 3-1/2 inches on the guage and fully open at around 19. mine will open fully at a lot less vacume with a manual hand pump guage
 

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Discussion Starter #5
I was talking to a friend of mine about this situation last night and he sugested that it might be my mass air sensor. once the RPMs are above 2600 and I ease into the throttle it doesn't over boost. it just happens at the low RPMs. He thinks that the mass air sensor is going bad, not measuring the propper amount of air going into the engine, so it over compansates by opening up the actuator, getting the turbo boost more air. Does that make any sense to anyone. As far as the adjusting the actuator rod, is it common that go out of adjustment. Thanks for all the help
 

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That is possible. The EGR can also do funny stuff with MAF readings because EGR gasses displace intake air. The actuator rod doesn't go out of adjustment unless the lock nut is loose. I could see rust on the exterior or sticking vanes on the interior causing poor action of the rod.
 
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