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Discussion Starter #1
Hi guys-

Long time lurker, first-time poster mainly because the car belongs to my daughter. I'm need to fix her car because it is beginning to get dangerous. Here is the deal. For some reason, the N75 valve keeps kicking in and dumping boost near the top end of the throttle then losing power pretty much instantly. She would get on the highway and nearly get run over.

I logged a couple of rides with an old version of VCDS that came with the car. If there s something else that I need to log to give a better picture of what is going on, let me know and I'll log it. I have worked a long time to get her car where I feel it is safe to drive and this is the last thing to fix. I feel like I have finally reached the end of my tech knowledge. I'm hoping there is a smoking gun you guys with all the experience can point out to me!

Beetle Logs

Any help would be greatly appreciated!

V/r,
-Bryan
 

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So, how would you describe the boost problem; if you push down the throttle, does the boost hesitate and then recover, have the boost kick in again or is it acting differently?

I had a boost hesitation issues; I ended up having a number of boost related parts, in soft failure mode and this was the cause of my boost issues. I found a number of parts being defective; read more here:

diverter-valves-stock-motor-apr-aftermarket-vs-stock-bosch.html

I ended up having a sticking diverter valve (wasn't leaking vacuum) and a bad Wastegate Bypass Regulator Valve (N75). I would consider testing your dv and your N75; I tried to use the conventional testing procedures, shown in the service manual but that didn't really help. My DV was sticking, which made the boost hesitate a bit; the N75, made the most difference, when replaced.

Have you done any testing; of the DV and N75? Have you done a full autoscan with VCDS for trouble codes?
 

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Hi Bryan,

Have you gone through your boost hoses to see if there are any tears or holes?

I had this exact issue with my 2004 GTI 1.8t going through a mountain pass. My boost hose between the charge pipe and pancake pipe got a little hole in it where it would only release boost on hard throttle, but (partially) seal right up during normal city driving. It was a very distinct noise.

My 2002 Turbo S blew the hose that runs across the top of the charge pipe to the diverter valve. It was a sneaky leak because the braided nylon was intact, yet a portion of rubber behind it was thin and unstructured. I wouldn’t have caught it by a visual check, alone. I only really felt and heard the leak when accelerating on a highway on ramp.

It might not fix the issue, but it’s a free and easy troubleshooting exercise.


Sent from my iPhone using Tapatalk
 

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Discussion Starter #4
Sorry, I should have mentioned that I have replaced the DV and the N75 because the plastic was starting to get brittle. I also replaced the hose that feeds the diverter valve from the turbo tube (charge pipe) due to it being blown out. I see that the N75 is being commanded to open up during the times that I heard the whoosh of air associated with the loss of power as denoted in the log files. Is there something I am missing here?

-Bryan
 

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You might graph your boost levels under wot; to compare what the actual vs the normals levels are.

This is shown in this video; tdi engine but principles are the same.


On a high milage vehicle; i would be testing the waste gate for normal actuation (smooth, not binding, actuate with vacuum pimp) and testing/checking for cracks on the hot side of the turbo. We are seeing cracks near the casting area by the w/gate lever, inside where the exhaust manifold bolts up to the turbo. I have replaced two ko3/ko3s turbos recently for low boost concerns that were hard to figure out; until i discovered the cracks on the hot side of the turbo castings. Needless ti say; it is hard to maintain boost with leaks, cracks in the turbocharger. If you feel the turbo impeller maybe damaged; you can undo the turbo inlet pipe and inspect the impeller for wear or damage.
 
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