BHW poor fuel economy PD TDI

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
I've been chasing this high fuel consumption issue for over a year now. The engine has a stage 2 colt cam(85000km old), EGR & MAF delete.Fuel and air filters were replaced, fuel and coolant sensor are new(the fuel sensor was bad), torsion value is 0, the turbo was replaced(jammed VNT). No smoke on cold starts. No knocking from the engine. I can't see any smoke under heavy acceleration. The MAP readings look good. The intake was ramoved and cleaned. I get a random limp mode once in a while for boost not reached. I ran 2 cans of Liqui Moli diesel purge already. The engine is smoother now but the fuel economy is the same. The car still has the cat converter. I get 9-9.5L/100km on long trips where I used to get 6-7L/100km. I feel like the car has a little bit less power than before but not a big difference. Any ideas where to look next? I was thinking the injectors but a lot of people are saying it would knock and blow smoke if it was the case. Any experience on a PD engine?
 

Tom in PT

Veteran Member
Joined
Jun 7, 2017
Location
Twilight Zone, WA State
TDI
2005 Passat sedan - SOLD; 2013 Passat DSG; both purchased new
When you say you used to get 6-7L/100km was that before or after "The engine has a stage 2 colt cam (85000km old), EGR & MAF delete." If you made these changes and then started to get poor fuel economy afterwards, perhaps those changes might have something to do with it. What is your highway cruising speed? at what RPM? Is your car 4WD (4motion)?
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
When you say you used to get 6-7L/100km was that before or after "The engine has a stage 2 colt cam (85000km old), EGR & MAF delete." If you made these changes and then started to get poor fuel economy afterwards, perhaps those changes might have something to do with it. What is your highway cruising speed? at what RPM? Is your car 4WD (4motion)?
it was after the car was modded. The car is a C5 Allroad. I usually cruise at 90-100kmh. That's around 1800-2000rpm in 6th gear. from those 85000km, around 40 000km were in Mexico and many short trips(5-10km trips where the engine didn't even reach operating temp). I guess that's what jammed the VNT.
 

50harleyrider

Top Post Dawg
Joined
Jun 16, 2007
Location
charleston,wv
TDI
2005 B5.5 TDI/geared BSM, BV43A turbo,stage 2 TDTUNING. 2005 5sp manual passat tdi stage 2 tdtuning,BSM delete. 2015 Passat TDI 6sp manual.
If you have access to VCDS, do a log especially for boost requested vs boost actual. You didn't mention if you have a tune. If you don't, get one. tdtuning has an excellent stage 2. I have it in my BHW. Your mods require a good tune IMHO to provide the best power and economy.
 
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stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
If you have access to VCDS, do a log especially for boost requested vs boost actual. You didn't mention if you have a tune. If you don't, get one. tdtuning has an excellent stage 2. I have it in my BHW. Your mods require a good tune IMHO to provide the best power and economy.
I have it tuned by Neurotuning. Boost requested vs actual is good. THe fuel economy used to be good. Sometimes it would get under 6l/100km(calculated at the pump) on long trips + a light foot.
 

50harleyrider

Top Post Dawg
Joined
Jun 16, 2007
Location
charleston,wv
TDI
2005 B5.5 TDI/geared BSM, BV43A turbo,stage 2 TDTUNING. 2005 5sp manual passat tdi stage 2 tdtuning,BSM delete. 2015 Passat TDI 6sp manual.
Something has changed obviously for your economy to suffer. Did you get the 6/100 prior to the tune or immediately after? Did you change the torsion value a little both positive and negative to see any affect? Try checking IP pressure. Are your injectors balancing fairly evenly in VCDS? Check that and let us know what your values are. Only change on thing at a time or you'll be chasing your tail. Also look for restriction in the air cleaner box bird screen. I usually remove them.
 
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Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
. Also look for restriction in the air cleaner box bird screen. I usually remove them.
I think you are referring to the snow screen and would be cautious about removing it wherever snow is a possibility. I had one fail and during a trip in a snowstorm the snow jammed up the air cleaner so badly it bent. Severe lack of power until I took it out. If an intact snow screen plugs up there is a secondary inlet to the plenum from inside the engine bay.
WV is probably safe. QC not so much.
 

Viggen73

New member
Joined
Mar 1, 2020
Location
Portugal
TDI
2002 Passat 1.9 tdi variant
Have you considered changing the in tank fuel pump? I'm having a similar problem, although when I do the math it's always around 6,8-6,9... But it's really shaky when it idles...
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
Injection quantity,
old(before diesel purge)
-0.47
-0.07
0.38
0.16

new(after diesel purge)
-1.34
0.21
1.27
-0.14


What do you guys think about these numbers? Somebody said I should try to readjust the injectors.
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
I think you are referring to the snow screen and would be cautious about removing it wherever snow is a possibility. I had one fail and during a trip in a snowstorm the snow jammed up the air cleaner so badly it bent. Severe lack of power until I took it out. If an intact snow screen plugs up there is a secondary inlet to the plenum from inside the engine bay.
WV is probably safe. QC not so much.
I will take a look at it again. It was clean when I replaced the air filter though.
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
Have you considered changing the in tank fuel pump? I'm having a similar problem, although when I do the math it's always around 6,8-6,9... But it's really shaky when it idles...
Have you tried to scan it? Do you have any codes? Why the in-tank fuel pump? it usually serves as a lift pump for 1-2 sec when you turn the ignition on.
 

Viggen73

New member
Joined
Mar 1, 2020
Location
Portugal
TDI
2002 Passat 1.9 tdi variant
Have you tried to scan it? Do you have any codes? Why the in-tank fuel pump? it usually serves as a lift pump for 1-2 sec when you turn the ignition on.
No codes whatsoever. The lift pump has been know to cause issues like poor fuel economy. I suppose even if it's a low pressure pump it helps provide an even flow of fuel to the PD.
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
No codes whatsoever. The lift pump has been know to cause issues like poor fuel economy. I suppose even if it's a low pressure pump it helps provide an even flow of fuel to the PD.
Thanks, I'll try to put a mension jar with diesel before the fuel filter and dip the 2 fuel lines in it and remove the fuel pump relay to see if it makes a difference. A run around the block will be enough I guess. This way I could tell for sure if it's related to the lift pump
 

Tom in PT

Veteran Member
Joined
Jun 7, 2017
Location
Twilight Zone, WA State
TDI
2005 Passat sedan - SOLD; 2013 Passat DSG; both purchased new
Have you ruled out non-engine-related, new and undesirable frictional losses in the drive train all the way to the wheels, including brakes?

How could a faulty lift pump cause a dramatic decrease in fuel economy? I don't get it.
 

stp359

Veteran Member
Joined
Mar 24, 2014
Location
Montreal, QC
TDI
Passat 4motion tdi 6speed
Have you ruled out non-engine-related, new and undesirable frictional losses in the drive train all the way to the wheels, including brakes?

How could a faulty lift pump cause a dramatic decrease in fuel economy? I don't get it.
the brakes on all 4 wheels are free. No extra friction anywhere.
 
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