S4 boost problems

[JoeeS3]

Hi there, bought an s4 b5 yesterday which has k04 turbos and k04 intercoolers and full exhaust system with 3inch downpipes.

I noticed on the way home if i planted my foot, boost would hesitate as if it cant work out whether to go! if i gradually accelerated the boost seemed to be a lot smoother. ive read a few things about the n75 valves and am looking at trying a mates working one to see if that is the problem? i also took off the wastegate vacuum pipe and it would boost to 15 psi. does this sound like a wastegate problem or n75 problem? i also had a boost spike to 24psi in 3rd gear on the way home when i put my foot down. twice when ive put my foot down with the n75 connected it has boosted to 24 psi and held it (but i let off when i realised what it was boosting at)

ive also disconnected my n75 and it boosts to about 5psi now

Cheers in advance

Joe

 

[slepy]

You should get it scanned to see if you have errors.

 

[Blue_Thunder]

What wastegate vacuum pipe do you mean? Just unplug the N75 from the loom and measure the boost. K04's have a wastegate spring pressure of about 6-7psi I think. Anything more than that, one of the wastegates has failed.

Slight boost/vacuum leaks can cause odd behaviour like you are experiencing.

 

[Blue_Thunder]

24psi at redline is usually too high with K04's. Think mine used to do 22psi at redline when I was running water/meth injection.

 

[cossie]

Sounds like MAF sensor fault. Disconnect the MAF and take it for a run, if it's running smoother then you need a new MAF. My S4 was doing the same 6 months ago and your symptoms sound the same.

 

[Bradderz_1988]

Throttle body boot split ??