Mpg help getting 35 mpg 04 bew 5mt

Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
So over the last few months I have been getting 35 mpg on b20, i go to about 1/4 a tank and fill, calculate milage manually. Including a 600 mile trip to cali i regularly do.

I have a new bosch maf, and 02 sensor (bought at reputable store) new fuel filter and getting a code saying 02 senor is rich...

I also changed my egr with a rebuilt one and no change.

Dog collar on the upper hose and new exit hose out of the turbo

Car has a newish vnt17 lowered on gti springs has a rebuilt 5mt.... (Make sure to always use thread locker on new axels)

And new brakes where i greased them myself (i work in a subaru shop part time as a hoby)
Any help to get 45mpg again... Also has a tune with a 2 bar map and racaro leather seats.... Save weight?
I am thinking its time i clean the intake system, i see active boost, and it hasn't changed, i do about 10 psi actual boost at 75mph
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
Also also the car once in awhile will sound like its missing and studder and be fine. Only when im crusing at hwy speeds, or sometimes climbing a hill at 60-70mph. Im guessing its because of a bad fuel/air mix. Car in general drives good and has no power loss going up hills even. Its more peppy than my 03 Forester.
 

DuraBioPwr

Veteran Member
Joined
Jan 28, 2020
Location
Eastern Washington
TDI
2004 BEW Jetta (5spd)
Yeah with your rich mixture codes would be looking at restrictions in the air supply. Chk all piping for leaks (pressure test), intercooler for oil/dirt buildup and your intake for carbon buildup like you mentioned. Its not the B20 lowering it that much. I run B100 in my 04 Jetta and get 43mpg in mixed driving.
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
How fast should oil build up in the intercooler? I remember there was some when i installed the turbo outlet hose.
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
The vnt17 was installed by the previous owner at 160k miles he claimed when he had the car it would get 45-50. The old stock turbo ran away but they saved the motor, when i got it i had it retuned for having the vnt17 with a two bar map added, the guy at the shop said it would make it run better. He never said what tune he put on it, and i had a boost leak when i was getting it done (turbo outlet hose) at this point i have a turbo pressure gauge installed, and can see 27 psi if i floor it (i never take it over 20 psi for the head gaskets sake) after i installed the downpipe i saw about 42 mpg consistently. I wish i kept the old tune, do you think tuners keep those?
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
Btw im at 235k miles, i had a 32 mile each way commute for 3 years and drive to cali 5-10 times a year.
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
On a side note i just did a capet swap from a jetta and had my headliner redone, it was leaking through the windshield water drain because of muck buildup, i had my sunroof seals sealed with rtv while it was opened up.
 
Joined
Sep 20, 2019
Location
Salem or
TDI
Mk4 golf tdi bew vnt17
Do you think a piece of carbon buildup could have broken off to hit the o2 sensor? And my gage for the turbo pressure is installed right before the intake hose on the plastic piping on top by the coolant reservoir.
 
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