Happy Friday!

I recently picked up an 08 R56 Cooper S (N14) and have been fixing its many issues.

I'm still chasing an underboost code (2885, boost pressure control deviation plausibility). It made no boost when I bought it (PO mis-routed vacuum lines while doing an awful job of replacing thermostat). Now it makes a max of ~2psi of boost. Have the half-engine warning.



So far I have:

- Tested wastegate (closes just fine with 15"hhg)

- Looked at turbo (no shaft play, spins great, CarFax shows it was replaced ~30k miles ago at the dealer)

- Replaced diverter valve

- Replaced boost pressure converter

- Replaced vacuum lines from pump-tank-pressure converter-turbo

- Checked out vacuum pump (sucks air when I remove that top brake booster line, brakes work fine)



Anyone have any recommendations where I should look next? Is a new turbo the only other possible solution here? I've done a ton of searching here and tried the solutions I've come across, but would love to find something I've missed before I put a new turbo on it.

Thank you!

 

I also did a smoke test into the cold side of turbo and there were no leaks.

 

I has a couple of other causes of this on my racecar that are not on your list

I had a partly melted and blocked cat, causing a pressure problem on the downpipe. Visually inspect the cat.

I had a failed temperature/pressure sensor, pn13627582551. If possible try swapping with one from another car, which is a 2 minute job. Number 5 on here https://www.realoem.com/bmw/enUS/sho...diagId=13_1206

 

Thank you for the reply @robbo mcs !
The top of the mesh in the cat looks great (I scoped it through the O2 sensor hole.

That pressure/temperature sensor is providing plausible data to both an Ultragauge and my scanner when connected - do you happen to know if they can fail in a way where they still provide plausible information but still cause an issue?

Going back and looking at the video from the borescope of the wastegate flapper operation, it looks like there may potentially be play in that as it swings closed.


Thank you!

 

I don't know about the sensor readings. What happened in my situation was we were chasing the cause for around a month, and had pretty much run out of ideas, checked everything. I wondered if it might be a sensor issue, so just randomly tried swapping that sensor from another good car in the workshop, which immdediately fixed the problem. We didn't try running the bad sensor in the other car (which we should have done) to prove it was actually a faulty sensor. I was just so excited to fix the problem I just assumed it was the sensor. It occurred to me down the line that it could have been a poor seal around the sensor as well, or poor electrical connection.