Boost Drop

[shiraken]

Hi,

I'm an owner of Golf4 GTI (1999 model, 1JAGU) in Japan. My G4 is tuned by Neuspeed.  From 1 year ago, sometimes the boost pressure drops to 0.2bar from 0.6-0.8bar during full accelleration.  On good condition, it stays around 0.6bar.

Checked all air hoses and found no air leak.  Replaced concerned parts with new one, like MAF, DV, N75, O2sensor, WaterTemp.sensor, FirePlugs, IngnitionCoils.  However the problem still exist!!  There is no fault code on VGA.

At the bad condition, I found that ECU stops to send a signal to N75 so that N75 will not deliver intake air pressure to turbo actuator.   So I want to know why ECU stops to send a signal to N75 by detecting a signal from a faulty sensor I suppose.

Checked the movement of turbo wastegate and its actuator is FINE.  I'm going to relace speedosensor this weekend as my last challenge.

I have no idea anymore!! 

Does someone give me any suggestion??   PLS HELP!!

additional comment:
Changed speedosensor, but the problem still exist.
Does someone replace wastegate actuator from original one to Forge actuator??  I need instruction how to replace wastegate actuator without taking off turbo unit.  PLS adivse.

[Addicted to boost]

I'm no master mechanic and 400 some odd people have looked at this... But what mods do you have? The stock turbo intake pipe has been known to collapse under full boost due to its soft construction. When you're at full spool pushing a good amount of boost, its creating such a vacuum on the TIP that it sucks in on itself. Check that out, it may be your problem. Thats all I can really think of... Only way to fix this is to get an after market TIP. I hope you figure out the problem though.

[shiraken]

Thanks for your suggestion.

Funally, I found the cause of problem.  Air house between intercooler and intake-mamifold was pulled out partly due to loosing clamp.  I could not see the point becasue it is located behind the bottom portion of front light unit.  After clamping the house tight, boost drop does not happen.

Anyway, thanks for your advice

[Addicted to boost]

Hey no problem, glad you found the problem!