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Discussion Starter #1
Hi all,
I'm just signing in so I'll rattle off some of the hanger queens here:

- 1996 Passat TDI (my first diesel)
- 2003 Jetta TDI (Given to #1 daughter)
- 2005 Passat TDI (Bought for the wife)

oh and as of last week

- 2007 F-250 Power Stroke

What brings me to the forum is that I'm trying to track down a loss of power in the Jetta. Limp home is almost surly at play here. VagCom shows no codes and I'm just digging in. At its worst, it will climb the hill outside my house in first gear and, maybe 8 miles an hour.
 

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Hi I'm new here too. I'm a car technician. Sometimetimes the boost pressure control valve brakes inside, so when you run the output test with VCDS it shows ok, but the mecanical part could be broken, and does not open. it's on the firewall. you have two almost same solenoids there, it's closer to the driver side.... it also called N75 valve.
Or it could be the MAF
 

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Hi, new to the site too. I just bought my 2005 Passat TDI about 4 months ago and really like it.
The fuel mileage is amazing (38-41 MPG).

It has about 74K miles currently and I plan on de-chaining it next spring.

Looking forward to learning more ways to keep it rollin'.
 

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Discussion Starter #5
Next Round ...

Ok, thanks for the info and tips. Last night I put the new N75 on after having tried to clean it with solvent and blow it out. I think the air pressure simply "jammed" the plunger deeper into the muck (a guess). Anyway, for $65 to WorldImpex, it seemed a pretty good deal. I took it on a test drive and it seems "much better" but I can't say that it is completely happy yet. From a stop, I nail it and the RPM's get to 3,000 and I can feel it hauling back. Not as bad as before but still noticable.

Here is the MAP chart. I am wondering if the overshoot on pressure is causing a cutback of fuel which is shown by the undershoot... How close should the curves be?
 

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If you step hard on the accelerator it's normal to see a spike but what I see is the boost going back and forth. If you roll into the accelerator does the graph look better? It could be sticking vanes or a sticking actuator. Check out hte FAQ article on how to test the actuator.
 

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Discussion Starter #7
Limp mode - Finding issues

All,
Thanks for the ideas to date. I bit the bullet and pulled the turbo off. Aside from the nasty issues of getting it off and then separating the exhaust manifold that was rusted on, I got down to the vane control ring. Sure enough, there was quite a bit of slop in the fit from the arm to the ring. The arm measures 0.247 wide in an unworn spot and 0.239 where it touches the ring. The ring was far worse; the slot should be 0.250 and it was worn open to 0.273. I have over 0.030 of play. The curve on the boost makes sense now. When the Manifold Pressure is buliding, all is well. When it reaches the limit, the valve dumps some vacuum but there is lost motion in the actuator/arm/ring assembly. By the time the vanes rotate back, I'm now shutting down fuel. When the boost comes down to the set point, it undershoots. Bottom line: The turbo is in serious trouble.

Tonight, I put a TIG Bead of stainless on the worn face of the ring and ground it flat. Tomorrow, I'll run a 1/4 mill up through it and restore the fit.
 
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