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Boost never higher than 2.5psi 535xi

I have owned a 2009 E61 for a few months and it feels quite powerful to me (other car is a 325i E46). I was looking at performance stats with OBD Fusion today and noticed I can never get my boost over 2.7 psi and from my reading it should max out closer to 9. There are no codes (scanned with ISTA). The check engine light sometimes comes on with a low boost code (30FF) if I give lots of throttle in a high gear and am below 2,500 rpm. Goes away once I restart the engine. Has only happened 5 times since August. I also have a bit of wastegage rattle. Seems that I’d boost was only going to 2.5 all the time it would give me that code much more often.

Attached are some logs. Anything else I should try to log?

Check all the charge pipe connections, especially the charge pipe at the throttle body. It could be cracked. Also, you can try to verify that under throttle the diverter valves close properly. You'll have to disconnect the crossover pipe between the diverters and the inlets, stick your finger in (not a lot of pressure) and have someone rev the motor. When the valves loose vacuum they should close (should also be closed with engine off after vacuum goes away).

That should give you a place to start.

Thanks, I will check out the diverters. I noticed one had been leaking oil so replaced the o-rings on it last week. I figured that if anything was leaking like this I would regularly get a code about boost. Seems to me the DME would know what boost level it wants to achieve but isn’t.

This week I will be blasting the intake valves so I got the manifold off tonight. Hooked up a vacuum pump to both diverter valves and noticed on both that I could blow through them at just under 100 mmHg (1.75 psi or .121 bar). Was reading some bmw technical literature which said the diverters should open when there is .3 bar in the intake manifold. Has anyone done a similar test on their diverter valves? I’m assuming this is normal since they are both identical. But they are both also the same age... seems to be that they shouldn’t open that early. I guess at WOT this wouldn’t matter though as there would be positive pressure in the manifold. Thanks

If I understand the construction of the diverter valves correctly, the only source that can change the position of the piston inside is the vacuum line from the intake manifold. The valve has a spring on the inside which vacuum in the manifold must overcome in order to move the piston and open the valve in order to bleed air out of the charge pipe. By that logic, I wouldn't think the DVs would never open if there is a positive pressure in the manifold, regardless of the pressure in the charge pipe.

Do you have a link to the literature that you are referring to?

Quote:

Originally Posted by Sirius815 (Post 1598212)

Do you have a link to the literature that you are referring to?

Unfortunately I don't have a link as it is some document I stumbled across online a few months ago when I bought the car and was looking for any technical stuff I could find. I attached it though, page 39 is the piece of info.

Check your wastegate arms. Just pull on them with engine off, pretty much every n54 will have worn out wastegates by 100k miles. I just pulled mine and they are completely worn. When it happens the wastegate flappers won't sit flat and won't be able to build boost.

Here is how bad mine were.

Quote:

Originally Posted by Kaane (Post 1598218)

Check your wastegate arms.

Thank you for the video. I tried to take a look at them tonight but since I have xDrive it is seriously impossible to get anywhere near the actuators or the arms going to them.

I performed two tests tonight with my vacuum gauge. In the first, you can see that the vacuum levels from my boost solenoids to my waste gates doesn't stay very high during wide open throttle. I would have expected them to stay >15" hg in order to build boost. Right around 2,400 RPM in third gear I get a 30FF code. If I punch it below or above that I don't get a code.

In the second test I wanted to make sure my vacuum pump is providing the full amount of boost. As you can see, shortly after full throttle the vacuum levels before the vacuum reservoirs drops significantly and takes a while to build back up. This makes me think that my solenoids are probably not the issue and that I have a leak somewhere or a pump that can't keep up with demand. Has anyone else done this second test? Shouldn't I expect to see a constant amount of vacuum before the solenoids? Thanks. ]

PS, I walnut blasted the valves this week but don't see any difference in performance. They didn't look like some of the worst I've seen out there, but I did have quite a bit of gunk to pick away around the edge of the valves/seats. I didn't notice any holes or cracks in the intake tubing but didn't do a smoke test.

It only takes 6 inHG of vacuum to close the wastegates. It's unlikely your vacuum source.

Quote:

Originally Posted by Kaane (Post 1598299)

It only takes 6 inHG of vacuum to close the wastegates. It's unlikely your vacuum source.

I agree, and was able to confirm that with my own actuators. I’m curious then why when I read on countless forums about people with tunes that they change their wastegates vacuum to 20”, sometimes even more. Seems to me that you would never need to go above 6”. If I very lightly blip the throttle my wastegates go from ~12” to 20”, only drops down if I do an extended WOT. Thanks.