hurricanesteve

Car is apr stage 3. Suddenly produced 10-12 psi max in lower gears and 6-8 psi max in 5th.

Things I have checked:
1. replaced BPV
2. replaced N75
3. pressure tested from turbo outlet to throttle body = holds until the plug I used blows off
4. pressure test from turbo outlet to intake manifold with all check valves blocked off = holds 5psi, but when I stop the compressor, there is a hissing that can be heard when I remove the oil filler cap (valve overlap?)
5. inspected for exhaust leaks, none visible or "smellable"
6. VAG-COM shows NO codes

Planning on doing today:
1. Compression test
2. Block line to wastegate from N75 (I imagine i have to be fairly careful if i do this, but if it makes more boost here, it will eliminate a turbine problem).
3. VAGCOM log intake temps, coolant temps

What other parameters would cause the ECU to limit boost? Why wouldn't it set a code?

thanks in advance,
s

Mike O.

If the actuator (brass plunger thing), rod or wastegate flapper are broken, it may stay open. That would lead to a low boost situation. Can you try pressurizing (10psi only) the silicon tube running to the actuator to see if the shaft moves?

Mike O.

hurricanesteve

tested the wastegate, the shaft definitely moves with pressure. Whether or not the valve itself is somehow stuck open or not, i don't know how to check without removing the turbo...

Audiboy

if so, that could indicate your catalytic converter maybe clogging up slowing down exhaust velocity, and hence turbo and building pressure on the oil seals - although I believe APR comes with a high flow cat.

Whatever it is, it really looks like the turbo is not spinning at full force, hence the higher psi at low CFM requirements and lower psi at higher rpm. Therefore as Mike mentioned, it could be the wastegate not closing fully, or anything that would cause the exhaust turbine to not spin fully - clogged exhaust, exhaust leak, worn out impellers, out of balanced impellers, or worn out bearings. If nothing is obvious from the outside, maybe the turbo is a dud

Phil type 951

let us know what you find out>>

hurricanesteve

no...same small amount as always...

Mike O.

remove the cat and you can see in with a mirror.