VW Golf mk5 Overboost problem :(

by **lsdlsd88** » Wed Feb 15, 2017 2:16 pm

Hi everyone,

I'm fighting with this VW Golf MK5, BKC engine 105ps.

I attach the VCDS log with a lot of stuff, basically the problem is an overboost condition, rising with rpm, starts at 3000+.
at 4200 RPM i have 0.5 overboost (request 2.0, actual 2.5). only error in ECU is overboost condition (intermittent)...

VNT obviously goes at its minimum 5%, but boost keeps rising.

I initially thought of a mis-adjusted vnt actuator, but then I noticed a really low value on MAF, it stays around 800 g/s with only a peak of 900 at 2500 rpm.

mechanically the car seems ok, starts and idle fine, regular servicing, etc.

I have a few ideas but I wanted to have your opinion BEFORE saying that to no influence you.

I attach a graph with some values but it's better if you open the csv and create your own.

Thank you all for helping

by **chefje** » Wed Feb 15, 2017 5:33 pm

lsdlsd88 wrote:Hi everyone,

I'm fighting with this VW Golf MK5, BKC engine 105ps.

I attach the VCDS log with a lot of stuff, basically the problem is an overboost condition, rising with rpm, starts at 3000+.
at 4200 RPM i have 0.5 overboost (request 2.0, actual 2.5). only error in ECU is overboost condition (intermittent)...

VNT obviously goes at its minimum 5%, but boost keeps rising.

I initially thought of a mis-adjusted vnt actuator, but then I noticed a really low value on MAF, it stays around 800 g/s with only a peak of 900 at 2500 rpm.

mechanically the car seems ok, starts and idle fine, regular servicing, etc.

I have a few ideas but I wanted to have your opinion BEFORE saying that to no influence you.

I attach a graph with some values but it's better if you open the csv and create your own.

Thank you all for helping

Did you remap the car mate? Maf seems normal to me. A small boost spike in the beginning. Besides that the boost got a smooth upward trend till the overboost. I suppose a look to the ecumaps will do the job

by **lsdlsd88** » Wed Feb 15, 2017 5:39 pm

yes car is tuned.

duration maps original (at least until 60mg). SOI original. boost ori. VNT tried to lower but no difference (obviously, it's already at 5% open.. wont go further).

I was expecting maf to be over 1000 at least! and it seems not to follow actual boost at all.

Honestly that make me thought about a camshaft timing issue. could it cause low maf and overboost because it's not "breathing" air properly? low V.E.? It's a car of a friend many miles away so I can't try it or check timing, but I want to give him some hint of what could be wrong. :D

by **chefje** » Sat Feb 18, 2017 6:57 pm

lsdlsd88 wrote:yes car is tuned.

duration maps original (at least until 60mg). SOI original. boost ori. VNT tried to lower but no difference (obviously, it's already at 5% open.. wont go further).

I was expecting maf to be over 1000 at least! and it seems not to follow actual boost at all.

Honestly that make me thought about a camshaft timing issue. could it cause low maf and overboost because it's not "breathing" air properly? low V.E.? It's a car of a friend many miles away so I can't try it or check timing, but I want to give him some hint of what could be wrong. :D

You can check the camshaft timing easy with Vagcom :thumbup: .

I would say if it's not because of the remap, check vnt vanes on sticky movement. Check als the egr and manifold and clean if dirty. Check also the turbo on shaft play.

Post also the ecu files if possible