[Flaze]

So i got a 635d (identical motor to 335d, and 535d, bi-turbo M57).
Ive been trying to diagnose this issue for around 2 months now and i honestly dont know what to check anymore.
The issue is that response AFTER 3k rpm feels extremely bad. The turbo takes around 2, sometimes 3 sec to even start building boost. How ever, if i give it beans from 2.8k, where the small turbo is still active, it will lite the big turbo almost instantly. I also have very good response low down with the small turbo. Peak power is also unaffected (390bhp), pulls well.
issue started intermittently and now its just perma fucked.

Things ive checked:
Literally all new vac lines;
Ran diagnostics, no codes;
Took intake pipes off to verify the turbo, and the bearing isnt fucked. Looks mint;
Tried running with crossover disabled, no affect.

I got no idea what to check anymore, really hope that someone has delt with this before and has some suggestions. Ive not found any forum threads with the same issue tho.

[lnxguy]

Replace both the pressure convertors and EV valve. Clean the little screen going to the vac pump.

Have you checked if the compressor bypass is sticking?

[Flaze]

Originally Posted by lnxguy

Replace both the pressure convertors and EV valve. Clean the little screen going to the vac pump.

Have you checked if the compressor bypass is sticking?

I wasnt able to verify the bypass visually, since i couldnt find it with a mirror, but, i can hear it closing when manually applying vac. It also doesnt bleed vac. so its probably fine... i could try again from under the car, maybe id be able to find it, but it probably works if it moves enough to make an audible thump.

Ive verified that both converters on the passenger side function properly.

could give the vac pump a cleaning, but obstructed pump would likely lead to low rpm turbo lag, since it would result in less vac at low rpm rather then high.

Yah, ive been thinking about the EGR as well (think thats what you mean with EV valve). I have it mapped out but its still there for mot reasons. Maybe theres a leak in the egr, which the ecu can see and prevents the turbo from responding properly...? Probably gonna pick up a proper blanking kit to test.

[lnxguy]

No, the EV valve is the electronic valve that controls the compressor bypass. Located under the pressure convertors.

[Flaze]

Originally Posted by lnxguy

No, the EV valve is the electronic valve that controls the compressor bypass. Located under the pressure convertors.

Was a good idea, but unfortunately, not the issue.
EV valve moves freely and holds vac, solenoid holds vac and has correct resistance.

Ive ordered and EGR delete kit, should get it next week. Maybe my EGR is leaking which is causing the ecu to trip somehow.