Boost/vacuum leak sound + fuel cut with P0234 code

[Flash1412]

Hello,

I recently bought a 2008 3 MPS with fuel cuts during pulls in 3rd, 4th and 5th gear at high RPMs. I had logging tool on me while buying the car and saw the overboosting condition P0234 together with a weird whistling sound coming from under the hood when under boost. Since I saw that everything else was OK, I bought the car.

Since then, I was trying to diagnose the issue, still with no proper solution found. As a first measure, I completely checked, undone and put back together all boost piping aswell as the intake before turbo, including the TIP, to still have the same whistling sound when under boost together with fuel cutting.

Here is a YT link to the sound the car makes: https://www.youtube.com/watch?v=JgugNAnQivE

I then bought a VersaTuner license and started looking at the tunes, especially boost control and boost limits. I then flashed the Base 93US/98EU Octane tune and since the boost limits are set a bit higher, the fuel cutting now occurs only in 4th gear and up. I then tried to unplug the electrical connection to the EBCS to see if the wastegate works and the answer is yes, the boost got to 0.6 bar (around 9 psi) only, so nothing wrong on that front.

In the logs, the MAF seems to be a bit low for what it should be with these boost levels and thus the load is lower than requested and I suppose that the ECU wants to compensate it with even higher boost which then leads to the boost fuel cut. But I would appreciate some more input from someone who knows a lot more on this topic. I also have a new EBCS on the way, so will try to replace it once it arrives.

I am starting to be a bit confused since there is an audible air leak sound/whistle, but the boost is too high and the MAF is too low. Maybe I am missing something obvious but would be very glad for your inputs.

Here are two log files of 3rd gear WOT pulls on Base 93US/98EU tune (no fuel cut occurs).

Thanks for your help!

[mituc]

There;s clearly a vacuum leak somewhere or the MAF has a problem. the boost is around 18.5PSI across the board and the MAF is measuring air for like 10-12. The overboosting code may have the origins in that, because the ECU is trying to achieve the commanded load which is directly proportional with the measured airflow, but because the measured airflow is low right now you're basically riding the throttle reduction boost limit for a base or even a high load tune.

At low loads the leak is not visible, which makes me think - considering also the sound you get (which makes me rule out the MAF for now) - that the leak is at a coupler somewhere and starts opening up only under high vacuum (from the turbo suction force). So it's clearly before the turbo somewhere.

[Flash1412]

Hi mituc,

thanks for the input! Yeah, the intake before turbo was also my suspicion - will investigate it further.