Under Boost with New Turbos

AlexR · 10-30-2021, 10:01 PM

Hey All,

I bought a 09 135i about a year and half ago. I knew that the turbos would need to be replaced when I bought it as they had the start of the wastegate rattle issue. Also, it threw the half check engine code for under boost a few times on the freeway. Last winter, I swapped out the turbos for brand new OEM turbos from FCP Euro. However, this did not seem to fix the under boost problem. I have a JB4 tune on the car, and when it is on the 13 psi tune, I cannot get the car to even build up 10psi of boost. It seems to top out at around 7psi. Any ideas on what could be wrong would be greatly appreciated.

AlexR · 10-31-2021, 02:22 PM

To follow up with some additional information: I bought a vacuum gauge today and T'd it into the the wastegate actuator vacuum tube (the tube that connects the outputs of the boost solenoids to the turbos). On idle, I pulled 14 in-HG on JB4 60% default wastegate position and 23 in-Hg at 100%. Are these reasonable enough numbers to to determine that the issue is not vacuum related?

Also, here is a JB4 log of a short 3rd gear pull on map 1. It actually never gets past ~7psi despite targeting 13.

10-30-2021, 10:01 PM	#1
AlexR Registered 0 Rep 4 Posts Drives: Mini R53 Cooper s Join Date: May 2020 Location: Midwest iTrader: (0)	Under Boost with New Turbos Hey All, I bought a 09 135i about a year and half ago. I knew that the turbos would need to be replaced when I bought it as they had the start of the wastegate rattle issue. Also, it threw the half check engine code for under boost a few times on the freeway. Last winter, I swapped out the turbos for brand new OEM turbos from FCP Euro. However, this did not seem to fix the under boost problem. I have a JB4 tune on the car, and when it is on the 13 psi tune, I cannot get the car to even build up 10psi of boost. It seems to top out at around 7psi. Any ideas on what could be wrong would be greatly appreciated.
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10-31-2021, 02:22 PM	#2
AlexR Registered 0 Rep 4 Posts Drives: Mini R53 Cooper s Join Date: May 2020 Location: Midwest iTrader: (0)	To follow up with some additional information: I bought a vacuum gauge today and T'd it into the the wastegate actuator vacuum tube (the tube that connects the outputs of the boost solenoids to the turbos). On idle, I pulled 14 in-HG on JB4 60% default wastegate position and 23 in-Hg at 100%. Are these reasonable enough numbers to to determine that the issue is not vacuum related? Also, here is a JB4 log of a short 3rd gear pull on map 1. It actually never gets past ~7psi despite targeting 13.
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