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TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

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Old January 7th, 2007, 16:45   #1
Yaco
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Default No Power Over 3,000 RPM

This is a problem with my 1997 TDI that went away for several years and has returned, but it is worse. When I am going up a hill and pushing the car past 75, the car suddenly loses power and the engine runs roughly. The car then has decreased power going up hills and will not go over 3,000 rpm. If I shut the car off and turn it on, it is back to normal, as long as I stay at lower speeds.

Previously I was able to turn the engine on and off and the problem would correct itself for a longer period of time. Now the problem will not go away.

I was at very high elevations in Mexico for several months, and the problem cropped up when I returned to lower elevations. That probably has nothing to do with anything, but I thought I would mention it.

The check engine light has gone on, but I am away from home and my mechanic and wanted to get a sense of the problem to see if I should get it addressed before my long drive home.


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Old January 7th, 2007, 18:18   #2
P2B
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Your TDI is going into limp mode due to a problem in the turbo boost control system. The ECU sees too much boost pressure, is unable to control the boost pressure, so it cuts fueling to protect the turbo and engine.

The most common causes are leaking boost control hoses or a failed N75 boost control valve. The N75 valve is mounted on the passenger side fender just ahead of the fuel filter, and has 3 control hoses - red, blue and black - connected to it. The red and blue hoses go to the turbo, and if one of them is damaged or disconnected that will cause your problem. Also check the electrical connection to the N75 valve.

You won't hurt the car by driving it home in limp mode, but it won't be much fun

Simon
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Old January 7th, 2007, 18:35   #3
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Don't forget the hose that is inside the ECU.
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Old January 7th, 2007, 19:13   #4
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Check the car with Vag-com. You might see a "charge control deviation" erorr of some sort if the N75 is bad.

There is always the possibliity of the maf going bad too.

Don't forget to verify if the check valve is working. (take note of the exact direction before removing to test, it's a directional component.) You should be able to blow though one end, but not the other. Can be cleaned with a light solvent and a light blast of compressed air.
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Old January 7th, 2007, 19:39   #5
whitedog
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I am guessing that Yaco is in Mexico right now. That would mean that Vacuum hose may be readily available, but an N75 may not be so easily available.

Isn't the Valve for the EGR the same valve? If so couldn't that be swapped over to get the car across the border and to someone like Runonbeer to help get things right?
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Old January 7th, 2007, 22:45   #6
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Trust WhiteDog, He knows his foreign parts (long story on his end)... The N75 may be hard to find in me-hee-co. Vaccum hose... never had to ask...
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Old January 8th, 2007, 16:05   #7
Yaco
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Default Thanks

Thanks everyone I appreciate the help.
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Old January 8th, 2007, 16:17   #8
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Quote:
Originally Posted by whitedog
Isn't the Valve for the EGR the same valve?
On A4 cars, boost and EGR are both vacuum controlled and the valves are the same.

On A3/B4 cars (like Yaco's), EGR is vacuum controlled but the wastegate turbo is controlled by boost pressure and the two valves are not interchangeable.

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Old January 8th, 2007, 17:48   #9
whitedog
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Quote:
Originally Posted by P2B
On A4 cars, boost and EGR are both vacuum controlled and the valves are the same.

On A3/B4 cars (like Yaco's), EGR is vacuum controlled but the wastegate turbo is controlled by boost pressure and the two valves are not interchangeable.

Simon
Thank you. I knew about the vacuum/pressure part but wasn't sure if they were still interchangable.
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Old January 8th, 2007, 18:54   #10
wny_pat
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The vacuum hoses get tiny pin holes in them. You can't even tell their bad. Just replace them including the short one in the ECU. It's right on time.
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