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Loss of boost spike?

Whitedemon

Ready to race!
Location
Miami, FL
ok, so I guess I'll be replacing the N75...hopefully this does it *fingers crossed*

If after replacing the N75 I still have the same issue then I'll adjust the wastegate rod.

Thanks for all your help!
 

Whitedemon

Ready to race!
Location
Miami, FL
Hey guys, it’s been a while but I’ve finally gotten around to working on this issue (was dealing with other things and work matter)

anyways, since I’ve put a pause on the issue with the high oil consumption for now(since looks like it will require to rebuild the engine head), I decided to tackle the boost issue.
Like I explained to @ROH ECHT on the other post, working on the car recently I noticed there was a small leak coming out of the MAP sensor bung, looks like the hole on my aftermarket tb pipe was too big for the oem o-ring on the sensor and wasn’t fully sealed, so what I did was I was able to find a slightly bigger o-ring (about 0.5 mm more) and replace it, this took care of the leak, I don’t see any more oil or methanol coming out of there (I have a water/meth injector bung right before so that’s what helped me notice it),however, this didn’t fix the boost drop issue.
So next, I did what both of you guys, @ROH ECHT and @Chumeta , suggested, added 1.5mm of preload to the wastegate actuator rod.
The results weren’t quite what I was expecting unfortunately, the boost stayed the same (~22.5 psi), however...one thing that did change was I was able to hit peak boost again when downshifting and opening up the throttle above 4K rpm, I was even able to peak at 26 psi when doing this, also...in 2nd gear I’d peak ~24 psi which id say is better than before, but the rest of the gears still the same when trying to build boost gradually, it never finds that peak...unless like I said, I downshift and apply throttle in high rpm and the boost spikes to 25-26 and drops back down to ~22.5 psi and holds it steady there....before I could do this without having to downshift.

What can you guys suggest?
 

Chumeta

Passed Driver's Ed
Location
Vitoria-España
Hello again. Check the conch-exhaust manifold or around the opening gate, that it does not have any cracks through which you lose pressure, as well as any leakage or wastegate problem or its air duct coming from the N 75
 

Whitedemon

Ready to race!
Location
Miami, FL
Hello again. Check the conch-exhaust manifold or around the opening gate, that it does not have any cracks through which you lose pressure, as well as any leakage or wastegate problem or its air duct coming from the N 75

thanks for replying. I’ve already checked all of that, haven’t been able to find any cracks or leaks, also there’s almost zero shaft play at the turbo so I know that’s not the issue, WG flapper doesn’t seem to be loose, I also replaced the N75 recently thinking it could’ve been that and made sure all lines were good...

BTW today I decided to try to add another turn of preload to the actuator rod (1mm) to see what happens.....no change. Boost stayed the same as before. It flat-lines once it reaches 21-22 psi. Could this mean the spring is shot or has weakened?
 
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ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
If you see no change, then boost pressure has likely exceeded the spring's rate. You should probably back it off to the previous adjustment. For if you fix something later, it doesn't over-boost.
OR...............
Have you looked at timing? What is the actual cam timing in MB 091 compared to spec? Should be 28.0° KW. I think 24.0° for the AXX engine. Also, what is the cam phase in MB 093 Block 3? If it is advancing timing too much, or the timing is off, it can reduce boost. It's worth checking.
 
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