Boost drop at high rpm

p1nk3y

New Member
May 29, 2021
8
0
0
Hello,
at 6.1-6.3rpm my boost starts to drop from 27 to 10psi. Before that everything is fine!
It happened as followed: I tried a 24psi map and everything went well. Then I stepped up and loaded up a 27psi map, and the car didn't boost right at around 6.1-6.3rpm. This happened everytime. I changed back to the previous 24psi map and the same thing started happening. Because of that, I'm pretty sure it's hardware related.
The engine is clearly trying to boost, with wgdc up to 100%, but it's just not happening. Something is hindering it, but only at 6.1k rpm.
DME Code:
30FC Turbocharger, charge-air pressure too low: leak tightness

Possible causes
Boost leak:
  • Leak tested the whole system with around 20psi, no leak
  • Tested oem and aftermarket blowoffs
  • Manifolds and CHRAs looks tight as well

Too much backpressure/induction resistance
  • Inspected cats and inlets with endoscope, everything seems fine
Broken turbos (compressor wheel scrubs against housing at high rpm)
  • I could endoscope one compressor, no visible damage
  • unlikely that both turbos are blown. AFR and STFT are similar across banks
Wastegates not regulating correct:
  • Vacuum system is tight (new vacuum hoses, system holds vacuum)
  • Both solenoids are new
  • Manually tested wastegates. Fully closed at 180-190mbar (BMW specification is 200mbar)

Other misc
  • Tried my original LPFP, made no difference

My setup:
  • 19t turbos
  • 2" inlets
  • walbro 525 pump
  • big fmic
  • original exhaust system: empty pre-cats, 200cpsi main cats
  • 2 steps colder + gapped spark plugs
  • alu cp
I would really appreciate some help, because I really am out of ideas. Thanks.

(Log is made with oem LPFP, rail pressure is higher with walbro LPFP.

 
Last edited:

GreyNBlueE92

Sergeant
Oct 3, 2018
266
92
0
27
OH
Ride
2007 E92 335i
Charge pipe O ring? Throw some teflon tape on there to test if you don't have one on hand, kinda ghetto but worked for me in the past.

Was thinking maybe the charge pipe hold down bolt isn't secure so when the engine moves it doesn't seal like it's supposed to. I think that's what was going on with my car, I lost the rubber bushing part of the hold down, it holds pressure when I tested it in my driveway. Intercooler is mounted to body and engine moves a bit when driving... Something to think about. Factory chargepipe has rubber elbow between intercooler and manifold. My CP had to be almost perfectly straight to seal against the throttle body.

Move things around and put physical pressure on things that might move when driving while pressure testing the car
 

JohnDaviz

Lieutenant
Jan 6, 2019
862
577
0
Ride
335i E92 DCT
collapsing inlets is also a potential issue.

One i know had the exact same issue just recently like OP and changing inlets solved the issue.
To prove that the inlets were the culprit he detached them from the turbos and did a test.
 

P33P33

Specialist
Apr 3, 2017
57
21
0
Ride
BMW 335i n54 e93
I'm leaning towards inlets collapsing too. Seen that with couple customers. If you keep driving and that is the case you'll end up with broken turbine shaft.