My boost pressure on my a4 has recently started to drop off,it peaks on 20 psi and was holding on 18 psi,now it's only holding boost till about 4000 rpm,by 5000 rpm its dropped off to 10-12 psi,i have fitted a new air mass meter and also a new dump valve,it has been on vagcom and showing no faults,has anyone got any suggestions please,thanks.

 

k03/k04 turbos are not big enough to be pushing 20psi near redline. They run out of breath up top. A k03/k04 turbo will always start dropping boost around 4500rpms to redline. Should be ~12psi at redline. A good shifting point with those small turbos is ~5500rpms (where the torque and horsepower graphs cross each other pretty much).

 

Thanks for the reply,so the drop in pressure is about right then,i thought this myself but i have been told by 2 garages it should hold its boost all the way,so i thought i'd better check this out.

 

ya he is right. it will always fall off. thats the downside to a small turbo. you get quick spool but then it falls on its face

 

Time for a K04

 

Thanks for the replys,also theres a fast tapping noise when you accelerate hard and turbo kicks in,thats what made me think there maybe a problem,but from what you say the turbo is working fine.

 

prolly just the check valve by the airbox. If so, it's normal. Audi/VW sure likes to over-engineer their engines.

 

worthless cup holder[:@]

 

Thanks,it does sound like its coming from that area,will the noise go if i replace the valve,its only recently started doing it.

 

not sure, mine has been doing it since I got my K04 and raised my boost levels. (now have a GTRS)