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    Thread: Used to get better mileage

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    1. 10-06-2012 08:12 PM #1
      2003 Jetta TDI with 204k+ miles and recently the mileage has decreased (last 10 fill ups). 5 years ago, I was averaging a consistent 46.2 MPG all the time and now I rarely hit 40MPG anymore. What made me write in is that I just put 600 miles on the car, all highway which normally results in the best mileage I see. Tonight it averaged out to 38.4. Is this just age?

      In case it's not age, here's what I've looked at hoping there's some maintenance I've missed

      1) The intake is not all coked up with carbon
      2) The air filter was just replaced
      3) The MAF was out of spec last year and causing the car to go into limp mode. I replaced the MAF last year and recently found it's still within specs
      4) Tires are properly inflated
      5) I switched diesel stations in case there is a difference in fuel now from a few years ago. I've seen no change in mileage.
      6) No engine codes or engine light
      7) The timing is within specs

      The car can breathe and the fuel was eliminated as a factor, what else could it be? aging injectors?

    2. Member Rockerchick's Avatar
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      10-06-2012 08:25 PM #2
      What transmission? How old is your fuel filter?
      Quote Originally Posted by TM87 View Post
      VW-making mechanics out of owners since 1957.
      The project - '84 Jetta 1.6TD, 186k+, fully rebuilt, Giles IP and injectors, 2.5" custom exhaust, 51mpg
      Hers - '03 BMP 20thAE GTI, 130k, 3" 42DD turbo back, Unitronic Stage 2
      His - '01 Jetta TDI, 135k. Now has 3 pedals, as it should!

    3. 10-06-2012 10:45 PM #3
      Manual transmission, fuel filter was changed about 15k ago.

    4. Member
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      10-07-2012 01:38 PM #4
      Quote Originally Posted by hovak View Post
      Manual transmission, fuel filter was changed about 15k ago.
      might be time to do it again..

    5. 10-07-2012 02:02 PM #5
      Im new to diesel but what about some injector cleaner? I would think that would be the cheapest route. Is something like that be available for diesel?

    6. 10-07-2012 03:20 PM #6
      I'll do the fuel filter this week, I hadn't thought that would be much of an issue, but I'll give it a shot

    7. Banned 85_305's Avatar
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      1999.5 Jetta TDI 5spd, MODDED
      10-09-2012 11:31 AM #7
      Is it original turbo? Original injectors? how many miles on injectors/turbo? The original 204k??

    8. 10-09-2012 08:10 PM #8
      Everything is original, turbo, injectors, etc. The only things I've had to change in 204k are the glow plugs, a few MAFs and an alternator (obviously oil, tires, fuel filter, air filters, etc).

      The car runs like a champ, just the MPG isn't what it used to be.

    9. Junior Member
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      1992 Jetta ECOdiesel
      10-09-2012 11:21 PM #9
      A can of diesel purge may help or your injectors could be getting old and tired and the nozzles are worn so you are not getting as efficient of a spray pattern from them any more leading to incomplete burn and reduced fuel economy. If the springs are worn they may be popping at a lower pressure and letting more fuel through at a lower pressure which once again leads to an incomplete burn and reduced fuel economy.

      Here is a link with more info on the nozzles and there is a link to a video showing how to do a purge.

      http://www.myturbodiesel.com/1000q/m...nozzle-FAQ.htm
      Last edited by DanV990; 10-09-2012 at 11:28 PM.

    10. Banned 85_305's Avatar
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      10-10-2012 08:59 AM #10
      Quote Originally Posted by hovak View Post
      Everything is original, turbo, injectors, etc. The only things I've had to change in 204k are the glow plugs, a few MAFs and an alternator (obviously oil, tires, fuel filter, air filters, etc).

      The car runs like a champ, just the MPG isn't what it used to be.
      I bet your injectors are just worn. Do you run diesel additive like diesel kleen to keep things clean/boost cetane? My mileage was going down the ****ter but went up when I swapped in better nozzles (old ones had 160k something like that...), and got even better when I upgraded turbo.

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