Diagnosing low boost?

GimmeBoost

Member
Joined
Jan 7, 2019
Location
CT
TDI
2013 6spd 4-door
I picked up my new-to-me TDI 12/29. It's a 6-spd 4-door slicktop with 60k miles from a used car "wholesale" type place. Remediation stuff was done, then it went to auction, now it's mine. I hooked up my OBD scanner and started watching how things work via Torque Pro last week and noticed that the car isn't boosting properly. The turbo spools up smartly to 15-17 psi but then immediately drops to 10-12psi and stays there. This is in the 2-3k rpm range with the engine fully warm. From what I've read I should be seeing 20-22psi pretty steadily at WOT in that rev range, correct?

No codes present, stored or active. The car seems to run well aside from this. The only issue I've noted was a stumble as if one cylinder wasn't firing on a cold start when the temps were in the 20s F that resolved quickly.

I did order a Ross-Tech VCDS that'll be here Thursday. I've read a bit and it seems to most likely either be a vacuum issue of some kind (leak or N75 problem) or an issue with the MAF. Is there anything else I should be checking? Is there anything in particular I should be looking at in Torque or VCDS when it arrives that'll help me narrow down the possibilities or do I just need to start getting dirty?

Thanks.
 

GimmeBoost

Member
Joined
Jan 7, 2019
Location
CT
TDI
2013 6spd 4-door
Got my VCDS. Fantastic tool. Went out and did some logging. 2400mbars, right where it should be. It would seem the information obtained via the dongle and Torque app is not necessarily correct. This is frustrating, but every tool has its limits I suppose.
 
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