overboosting and bad fuel economy... boost/maf map

leafs

Veteran Member
Joined
May 28, 2018
Location
canada
TDI
alh
Can you guys tell me what you guys think is going on? Bad maf, something up with the turbo, maybe both? Car is 5spd converted alh.

Run number 1. As you can see the maf appears to be out of whack at idle. Went limp mode at like 3000rpm 4th gear no CEL.



Pulled over and restarted, which fixed the limp mode. Run number 2. Limp mode again same rpm/gear this time resulted in a cel with overboost intermittent code.



Let me know what you guys think because I don't have a clue. :)
 
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Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
Maf looks fine. At idle it'll do that when the EGR valve closes. Being as it's registering over 800 I say it's good.

You are however constantly overboosting. Make sure your turbo actuator isn't sticking, verify start/stop vacuum, and verify at idle you have at least 20inhg vacuum.
 

leafs

Veteran Member
Joined
May 28, 2018
Location
canada
TDI
alh
Maf looks fine. At idle it'll do that when the EGR valve closes. Being as it's registering over 800 I say it's good.
You are however constantly overboosting. Make sure your turbo actuator isn't sticking, verify start/stop vacuum, and verify at idle you have at least 20inhg vacuum.
You think the fact that I don't have a cat converter could have something to do with it? No back pressure against the turbo maybe. Can overboost even cause bad fuel economy. I thought more air being packed in there = better.
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
No that more so pertains to gasoline cars. I have no cat and have much better boost control.
 

leafs

Veteran Member
Joined
May 28, 2018
Location
canada
TDI
alh
Turns out the actuator was out of adjustment.

Started moving at like 3" and stopped at 15." That resulted in like 2-3mm of the vane lever not being available. Made the adjustment and no more overboost code but haven't had a chance to hook up vcds logging again. Seems like I have more power too. Probably a more ideal air/fuel ratio. Going to see if it helps the fuel economy issue.

Hope it didn't damage the turbo or the engine from running lean. I was relatively careful with it because I knew about the overboost condition but wasn't about to screw around with it during the winter. The last owner really got dicked around by the shop he was taking it too. That's two things now.
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
I'm sure the turbo is OK. Glad you found the issue. Happy trails.
 
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