E61 535 boost issues

[MSB123]

Symptoms:
On a cross country trip, car kept throwing a half power light which would go away after restart. It also only gave boost up to 7.5 psi.

Got home and replaced MAP and Boost sensors, half power light is no longer appearing.
But, the car still won’t generate more then 7.5 psi of boost, and the exhaust gas is now a bit denser then I remember it being last I looked.

Could this be a failed turbo?

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Just a bump so I get notifications

[pbonsalb]

Start with reading the codes. Could be a lot of things.

[MSB123]

Just getting a p30ff low boost. Also occasionally triggers an o2 sensor code (they are all brand new genuine sensors so I suspect it’s a fuel/air imbalance due to a lacking turbo)

[pbonsalb]

Normally when a turbo fails, you get a lot of oil smoke out the exhaust. Unless your car is smoking, I doubt this is your problem. You could have a wastegate flapper that is no longer seating properly — that is part of the turbine housing and can’t be fixed without removing the turbo. On a high mileage car, I would just replace both turbos with rebuilt units if you have to remove one.

Could also be an intercooler hose, a wastegate hose — they get brittle and crack, the wastegate controllers but you replaced those. O2 sensor code could be from an air leak. Smoke test can help find the leak. Many owners have had injector problems and fuel pump problems.

These are great cars when sorted out, but most need a lot of sorting. You can find threads on the weaknesses and start doing preventative maintenance. I still maintain the 08 E61 535xi that I gave to a friend a couple of years ago after owning it for 10 years. I did a lot of preventative maintenance including replacing the turbos.

[MSB123]

Alright- for the fun stuff-
Car has been smoke tested. Nada. New index 12s. New hpfp, new lpfp/filter.
I am the second owner of the car, previous owner put 200k and I have put 15k.
I’ve done all of the above, car has been serviced at bmw every 6 months since 2009 until I purchased it and began doing my own work.
I will vacuum test the entire system with tracer smoke to try to figure it out next weekend, at this point I might do all new vacuum lines and a new chargepipe/intercooler piping

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I don’t normally do turbo cars, and this is more of a reminder why.

[pbonsalb]

I doubt the intercooler hoses are leaking. Brittle vacuum lines around the wastegate controllers are likely if original. Bypass valves not fully inserted are easy to check. Leaking wastegate flapper valves is likely if original and they are hard to test but with a lot of work you can get to the actuator rods and tighten a couple of turns.

Replacing the turbos at 215k miles makes sense. I did it at 150k as preventative maintenance since I planned to leave the car at another house where I did not have a full shop. That was a big job. Subframe has to come down and passenger axle out. Given that I would be in there, I also did the oil pan gasket and rod bearings and motor mounts.

PCV valves on the valve cover should be replaced as well if doing turbos. And if you have not done a walnut shell blast of the intakes, it is definitely needed. There was a lot of goo at 90k miles on my car. With the intake manifold removed, updating the low pressure fuel sensor to the new one is a good idea.

Great cars if sorted out. I had a JB4 piggyback on mine to wake it up a little. It was my wife’s car so that was the only mod. Turbos do complicate things and add a lot of heat to the engine bay. I like them for the added power, though — my 3 current cars are turbo. 2 turbos like the N54 is more complicated than 1 turbo like the N55.

[MSB123]

Already done PCV and walnut blasted at 205. Rod bearings seem like a logical step.

[pbonsalb]

And with the work to get in there, install a set of quality rebuilt turbos. You could do inlets as well. I did not and did not upgrade the turbos either since it was not my personal car.

[MSB123]

Alright.

Just did vacuum lines. No dice. Still 6.5psi maximum. Throws half power light as well.
Wondering now if it’s a stuck wastegate. I got a code:
P30FE : Boost Control, boost pressure to high error wastegate 1-clamped.

Wondering if the wastegate is perhaps stuck open?
These turbos I have learned were done at 150k so I doubt they are dead.

[pbonsalb]

Check wastegate actuator arm nut, vacuum/pressure test hose from actuator to solenoid valve to verify actuator is working. Replace any leaking solenoid and actuator hoses. Try swapping solenoids to see if problem moves from one turbo to the other assuming your code has identified one WG as the problem.

It is possible but unlikely that your WG flapper valve has broken in one turbo. Some rebuild kits one with DIY weld flappers but if new turbos were installed by a BMW dealer 65k miles ago this would not be an issue.

I would also check the compressor outlet path to and from the intercooler for a boost leak. Smoke testing and/or pressure testing are the common ways of visual shows nothing.

[MSB123]

Will do. Both WG’s move when I manually apply vacuum…

[pbonsalb]

Then I would focus on the solenoid that controls the actuator. Your previous smoke test should have exposed any issues with the compressor outlet path to the engine, but sometimes you need pressure to open up a leak.

[MSB123]

Are the solenoids not redundant? Two in line.
Is there an easy way to test them?

[MSB123]

Interesting news.
I disconnected the diverter valves, plugged all vacuum leaks, and connected the wastegate actuators both with a t fitting directly to a hand operated vacuum pump. Pulled 10 in hg of vacuum (checked rear wastegate And the actuator rod moved all the way at 8 ish. Then drove the car (being very careful to only pull vacuum with the pump when wanted and quickly releasing it.

With this setup I only got 7psi of boost.
Maximum. Even tried higher vacuum levels and still the same thing. Leads me to believe either a turbo is bad or I have a cracked chargepipe. Like majorly cracked. But it would probably be the one going around either the front or back of the engine and I’m not sure how to remove those. Will try to do so this afternoon.

[pbonsalb]

I don’t think a charge pipe wraps around the back of the engine. I think that is the inlet pipe for the rear turbo. The charge pipe is a 2 into 1 pipe on the turbo side of the motor that goes forward to the intercooler entry on the same side. You could follow the intercooler discharge to the throttle body—could be loose there but that should have shown up in a smoke test or maybe it needed some pressure for a leak to open up. Most smoke tests are unpressurized.

I think 7 psi may be in the stock range. There may be MAP control rather than a specific PSI so in colder weather a slightly lower number might be expected rather than the 8.8 psi one should see in warm weather.

I don’t think any solenoids are redundant. Might be 1 for each turbo but a common reference.