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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old March 21st, 2011, 19:00   #1
chaloux
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Location: Gravenhurst, Ontario
Default Need thoughts on possible boost leak - low boost, no power, etc...

So a few weeks back, on my morning commute, once I was almost onto the highway I realized that I had no boost/low power (babied it until it was warm, then nothing). I floored it a few times on the highway, and eventually the power just kinda popped back to normal.

Anyway, it didn't happen again until yesterday after doing some ice racing. Upon leaving the lake, I realized I had no power. "No big deal," I thought... it'll just come back after some pedal to the metal.

Nope.

So I checked over the vacuum system - no leaks, has 25mghzhh whatever that is, the VNT actuator starts moving at 5 and finishes right around 20 - not perfect but pretty normal. I tried removing the check valve, no difference.

I have a straight exhaust and know that the turbo isn't changing because when I shift I'm not hearing the bark/whoosh that happens when the vanes close normally. At first I didn't realize this, so I thought it was a boost leak. Now I think it's my N75, which I'm looking for in the Ontario section (or an N18, same thing). I'd test mine, but trying to remove it I broke the VAC nipple off - damn it! So I need a new one anyway.

My dad's car(s), URS cars, have an N75. It looks different (ghetto) but it has the same connector and three vacuum nipples. I hooked it up but I have no idea what goes where because it's not labelled. Anyway, VAGCOM is telling me that my MAP is off - actual coming in way under requested when I step on it. If I hold it for 5 seconds I get limp mode.

Also unplugged the MAF, no difference at all.

So my question is, what do y'all think? Sound like an N75? I was under the impression that N75 failures cause overboost.

Any input is appreciated.
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Old March 23rd, 2011, 07:03   #2
chaloux
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Seriously? No one has an opinion on whether these are typical failed N75 symptoms?
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Old March 23rd, 2011, 07:12   #3
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Can't say much for being a mechanic, but if your VNT is not moving freely you probably need a new VNT actuator or your turbo vanes are sticking.

You should test your VNT actuator by putting a vac.pump on it and testing to see if it can hold 20"mmHg (with no bleed down).

Also, remove the VNT actuator arm from the turbo (little C-clip) and see if the lever on the turbo moves freely throughout its whole range. If it doesn't, your turbo needs to be cleaned.
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Old March 23rd, 2011, 07:13   #4
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by the way, what error codes is VCDS giving you?
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Old March 23rd, 2011, 13:04   #5
chaloux
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Actuator moves fine, tested its range with a vacuum pump, moves as it should (starts at 5"mmHg, finishes at 20"mmHg). I didn't check to see if it bled down.

Would this not also indicate that the turbo lever is moving fine as well, since it is moving when it should?

Thanks!
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Old March 23rd, 2011, 13:07   #6
chaloux
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I'll have to get back to you on the codes... basically the one that says manifold pressure is screwed - this is only if I floor it for 5 seconds or more and then goes into limp mode. I'm assuming it's because my actual MAP is far lower than my requested MAP, like 600mbar lower.
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