[kwseattle]

I've been battling this for a couple of months.

2011 M Sport, stage 2 tune from DUDMD, EGR, SCR, DPF delete with Buzzken downpipe, xHP transmission tune.

Car pulls hard until about 2800 RPM and then all of the sudden the torque drops off and the acceleration slows down quite a bit. It's most noticeable in 3rd+ gears. I'm going to be looking at some data logging soon to see if I can get anything useful.

As of now I've replaced all vacuum lines, the two pressure converters, the electric valve that actuates the compressor bypass valve, the charge pipe (upgraded with the AARodriguez one), and cold side intercooler o ring.

When changing the vacuum lines I tested the changeover valve with a vacuum tester and it held vacuum and the piston retracted just fine, so I assume it is not that.

After everything the issue is better, but still present. Does anyone have any suggestions?

Thanks.

[Yozh]

As discussed, make sure your SCR is indeed gutted.
Then datalogging would be essential. Requested vs actual boost vs exhaust pressure. 2800 rpm is an interesting spot as this is where the compressor bypass engages. I would also make sure it's not physically sticking. You can observe its rod movement from underneath with covers off.

[kwseattle]

Torque and related Realtime Charts weren't able to pull anything very useful at the first attempt, I'm going to try again tomorrow with some better plotting configuration.

The compressor bypass on the front of the engine has a rod that retracts as well? I will have to look into that and see if it's working properly.

Good thing I have a warranty, the compressor bypass is like $500.

I'm fairly certain the SCR cat has been gutted, all of the OEM welds on the exhaust look like they've been done robotically (and given the production volume BMW has I'm going to assume this is true). The weld on the rear of my SCR cat looks very much so like a hand weld that has been cleaned up with a grind wheel and wire brush. I will contact my tuner just in case.

[Yozh]

Yeah if you look from below you between engine and intercooler looking at the boost feed pipe you can see a bit of a rod from compressor bypass. Test it with a hand pump and see if it moves. And holds vacuum.

[kwseattle]

Great, I will do that!!