[Max335d]

I noticed my boost starts to go down closer to redline 4000+ RPMs especially happens in a lower gear like third or second. Most noticeable when I pin the throttle. When I give it gas in fourth at like 1500 RPM, it’ll carry 26 to 28 psi up until the end of the gear and it will slowly die off. What’s the reason for this. My car isn’t tuned it just has a turner motersport intake and an atm charge pipe (into throttle body). Not sure why it does it it will make perfectly fine boost up till then and it’s not dramatic cut off. When I pin it at like 20mph it will top out at like 20psi through the higher rpm’s in second and third. 2011 335d m57

[maryjane]

Pressure converter. There's USUALLY a splice in the vac line on the passenger side right at the A/C compressor. Disconnect that vac line and go for a drive to see if it stays.

[Max335d]

Originally Posted by maryjane

Pressure converter. There's USUALLY a splice in the vac line on the passenger side right at the A/C compressor. Disconnect that vac line and go for a drive to see if it stays.

This can break and it won’t throw any codes?

[maryjane]

PM me i can give you my number for some testing to do.

[lnxguy]

Originally Posted by Max335d

This can break and it won’t throw any codes?

You'll be fine, you're not going to break anything.

[BradleyN55]

Originally Posted by maryjane

Pressure converter. There's USUALLY a splice in the vac line on the passenger side right at the A/C compressor. Disconnect that vac line and go for a drive to see if it stays.

Yes, been there done that exactly.