tdi_allan
Veteran Member
- Joined
- Feb 14, 2003
- Location
- Chicago, IL
- TDI
- 2003 Jetta Wagon, 2003 Jetta Sedan (Lemons racer), 2010 Touareg
I have read a number of recent low power threads with great interest, as I have recently experienced an intermittent underboost issue. Let’s retrace my steps...
1) Noticed initial lack of top end power. No codes at this point. Checked and replaced all vacuum lines but the one from the N75 to the turbo. Performance improved slightly.
2) A couple of weeks later, tested the N75 - fail. Replaced both N75 and N18 “while I was in there.” No change in performance. Still no codes.
3) Got around to replacing the N75 to turbo vacuum line a couple of weeks later. The old line was clearly worn. Performance improves...for a while.
4) Finally a code - P1550, intermittent underboost. Tested VNT actuator - did not hold vacuum. Replaced actuator - performance improves. Code cleared and stays that way...for a short while.
5) Underboost code is back. Put up with it for a while as I had little time to mess with it. As I planned my assault on the charged air pipes, decided to try one more thing. I plugged the vacuum line to the anti-shudder valve. All underboost symptoms disappear. Installed new ASV - restored power remains.
So a pretty standard TDI power loss diagnosis and repair, right? Well, I forgot to mention a step:
0) Replace súper leaky exhaust flex pipe and repair other exhaust leaks which have existed for quite some time.
I am convinced that my delay in fixing the flex pipe leak created conditions that accelerated the demise of the vacuum lines and N75. The VNT actuator failure may or not be related to the failure of other components.
Hopefully this will help someone in the future.
1) Noticed initial lack of top end power. No codes at this point. Checked and replaced all vacuum lines but the one from the N75 to the turbo. Performance improved slightly.
2) A couple of weeks later, tested the N75 - fail. Replaced both N75 and N18 “while I was in there.” No change in performance. Still no codes.
3) Got around to replacing the N75 to turbo vacuum line a couple of weeks later. The old line was clearly worn. Performance improves...for a while.
4) Finally a code - P1550, intermittent underboost. Tested VNT actuator - did not hold vacuum. Replaced actuator - performance improves. Code cleared and stays that way...for a short while.
5) Underboost code is back. Put up with it for a while as I had little time to mess with it. As I planned my assault on the charged air pipes, decided to try one more thing. I plugged the vacuum line to the anti-shudder valve. All underboost symptoms disappear. Installed new ASV - restored power remains.
So a pretty standard TDI power loss diagnosis and repair, right? Well, I forgot to mention a step:
0) Replace súper leaky exhaust flex pipe and repair other exhaust leaks which have existed for quite some time.
I am convinced that my delay in fixing the flex pipe leak created conditions that accelerated the demise of the vacuum lines and N75. The VNT actuator failure may or not be related to the failure of other components.
Hopefully this will help someone in the future.
