Low mpg ALH help diagnosing with VCDS

libound

Veteran Member
Joined
Aug 23, 2013
Location
Long Island NY
TDI
2003 Jetta TDI GLS 5sp
My jetta has been getting "okay" mpg since I bought it a year ago. It's 5 speed and I average about 39mpg, even with mostly highway driving. I use all the proper driving "techniques" so I'm a little puzzled. I just got a vagcom cable and I'm wondering if there is an diagnostics I can do to see if anythings out of whack.

My timing is slightly advanced from the center line and injection quantity has been adjusted to 4.0. Anything else I can check?
 

Rembrant

Veteran Member
Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
Yeah, like Bob mentioned...start by checking your ALH control health....MAF sensor, Boost control, IGN/INJ timing, etc...

If the MAF numbers are funky, I'd replace it...they're cheap. This is of course assuming you have no air flow restrictions to begin with (intake clean?). I'm on my second 2003 ALH TDI, and they both had faulty MAF's when I bought them.

I'm currently getting 52mpg without trying all that hard...no hyper-mile techniques yet.

Starting with some VCDS checks is a good idea imho. Make sure all the controls are working as they're supposed to, then move on to mechanical stuff...lots of gains to be had if you're currently at 39mpg.
 

jjcsnlynn

Veteran Member
Joined
Nov 18, 2007
Location
Felton, DE
TDI
02 & 03 Jetta TDI,99 Beetle TDI, 04 Chevy Duramax 2500HD 4x4
Check your CAT for blockage. My 1Z got about 10 mpg more once I changed the CAT.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Check the Snow Screen on the air filter box snorkel ........ prolly loaded with road debris!
 

deejaaa

Veteran Member
Joined
Apr 15, 2007
Location
Baytown, Texas
TDI
FOR SALE, 2002 Jetta GLS, 5 speed
i can get 55 easy but over the last 2 years my average is 59.6. tires, 15's, made a big diff to me. aired to 50. have 89,000 miles on them and the rears can still pass inspection.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Tire size

Quick question.
What size tires do you have?
I was thinking to go 2 sizes larger next set of tires.
2003 Jetta TDI wagon.
Stock is 195/65-15
I was thinking 215/65-15 and getting the speedo calibrated.
This should drop my highway rpm down about 100 rpm.
Best I ever got was 53 on the highway in 11 years.
Don't think I want to go that high on the pressure. :)

TIA
Rich W.

i can get 55 easy but over the last 2 years my average is 59.6. tires, 15's, made a big diff to me. aired to 50. have 89,000 miles on them and the rears can still pass inspection.
 

SD26

Veteran Member
Joined
Jan 7, 2010
Location
WI
TDI
1998 Jetta TDI 5sp, 2002 Jetta TDI 5sp
Quick question.
What size tires do you have?
I was thinking to go 2 sizes larger next set of tires.
2003 Jetta TDI wagon.
Stock is 195/65-15
I was thinking 215/65-15 and getting the speedo calibrated.
This should drop my highway rpm down about 100 rpm.
Best I ever got was 53 on the highway in 11 years.
Don't think I want to go that high on the pressure. :)

TIA
Rich W.
You'll be trying to push more air around the wider tires, and you'll increase the amount of air that has to move under the car. I've tried that on other vehicles before, and I lost mileage.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2003 Golf GLS (2005 Mercedes E320 CDI)
Take a look at my fuelly numbers for a clue as to what made a significant improvement on fuel mileage for my car:

http://www.fuelly.com/car/volkswagen/golf/2000/uhoh/333519

Scroll down and look at the Logbook entries.

I'm still trying to figure it out. I'm running the car harder now that it's got a LOT more performance, and the fuel mileage is lots better! (always use the same fueling station, even the same pump) Can't wait to get new nozzles and have the injectors calibrated (not to mention set the TIMING, which I have yet to do since the TB job [heck, it's been running and starting great, and, clearly, getting good fuel mileage, so this hasn't been a big priority]).
 

Rembrant

Veteran Member
Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
I'm still trying to figure it out. I'm running the car harder now that it's got a LOT more performance, and the fuel mileage is lots better! (always use the same fueling station, even the same pump) Can't wait to get new nozzles and have the injectors calibrated (not to mention set the TIMING, which I have yet to do since the TB job [heck, it's been running and starting great, and, clearly, getting good fuel mileage, so this hasn't been a big priority]).
What did you do to get a lot more performance?
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2003 Golf GLS (2005 Mercedes E320 CDI)
What did you do to get a lot more performance?
Per my Logbook: EGR and intake cleaning. I think that you can relate to that:D

I cannot say for certain that this will be the case for the OP, but for me it's a pretty stark change, one that clearly coincided with that work: no change in driving conditions (other than a slightly heavier foot). My wife's car, however, hasn't responded like mine has; her's, however, ran really well before (EGR and intake cleaning) and her fuel mileage was already several MPGs above mine.
 

Rembrant

Veteran Member
Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
Per my Logbook: EGR and intake cleaning. I think that you can relate to that:D
Yeah, mine was plugged up as well...as was the EGR cooler, and the intake ports in the cyl head. I don't know how much all this cleaning contributed to the now excellent health of my ALH. I did many other things during the rehabilitation process, so I can't say how much each item helped individually.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
i can get 55 easy but over the last 2 years my average is 59.6. tires, 15's, made a big diff to me. aired to 50. have 89,000 miles on them and the rears can still pass inspection.
Not unheard of, but those numbers are exceptional
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Thanks for the reply.

I was wondering about more rolling resistance with wider tires.
Didn't think about air drag.
Rich W. :)

You'll be trying to push more air around the wider tires, and you'll increase the amount of air that has to move under the car. I've tried that on other vehicles before, and I lost mileage.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Interesting web site.
Seem like you slightly lost MPG after demufflerizing the car?
I read a suggestion to lengthen the turbo actuator arm if you run open pipe.
Less resistance to the air flowing through, more boost needed??

Thanks for the feedback.
Rich W.

Take a look at my fuelly numbers for a clue as to what made a significant improvement on fuel mileage for my car:

http://www.fuelly.com/car/volkswagen/golf/2000/uhoh/333519

Scroll down and look at the Logbook entries.

I'm still trying to figure it out. I'm running the car harder now that it's got a LOT more performance, and the fuel mileage is lots better! (always use the same fueling station, even the same pump) Can't wait to get new nozzles and have the injectors calibrated (not to mention set the TIMING, which I have yet to do since the TB job [heck, it's been running and starting great, and, clearly, getting good fuel mileage, so this hasn't been a big priority]).
 
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