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  • Poor fuel economy 1.8T

    Hey guys just a quick inquiry. I searched a bit about bad fuel economy and found some things I can check out. Basically since I did the whole SAI/N249/N80 and added the catch can and 2.0T coil packs I'm only achieving about 300km's per tank, I used to get about 425 or so even with the roof rack.

    Gonna try a couple things:
    clean and recharge air filter
    replace fuel filter
    remove "T" from line at FPR for boost gauge. When I put it in car was basically stock, now I have open ports on the intake mani so I'll try that.

    Any other suggestions? I don't smell gas. Car seems to run pretty normal. Idles normal although every once and awhile at a light I'll feel a quick stutter...nothing serious.

    Thanks!
    Bagged 2004 Jetta GLS 1.8T Stage 2 Unitronic, 2016 Tiguan R-Line , S13 SR20DET, Mk2 VR6 Project, 2011 Dodge Ram 1500

  • #2
    Re: Poor fuel economy 1.8T

    I assume since you are "recharging" your filter it is an oiled filter? I would recommend a dry filter or else that oil has a tendancy to coat the MAF sensor and give false readings. You could try giving it a clean in the MAF cleaning solution and see what happens.
    Your fuel trim levels could be outta wack also and dumping in more fuel than necessary if your rear O2 is coded out and you haven't resistored the N80 properly and coded it out specifically. (your uni stg1+ won't have this unless specifically requested and paying for it usually)

    In reference i have the Gonzo tune and got them tuned out accordingly and get ~600km/tank typically in the city and more on the highway
    Last edited by MechEngg; 06-25-2014, 08:47 AM.

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    • #3
      Re: Poor fuel economy 1.8T

      Could be worth putting in a new primary O2 sensor too. They do wear out eventually and give poor economy.

      Sean, the rear O2 sensor has no effect on how the engine runs, its merely there to ensure the cat is working properly
      Last edited by onceover; 06-25-2014, 08:50 AM.

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      • #4
        Re: Poor fuel economy 1.8T

        Originally posted by MechEngg View Post
        I assume since you are "recharging" your filter it is an oiled filter? I would recommend a dry filter or else that oil has a tendancy to coat the MAF sensor and give false readings. You could try giving it a clean in the MAF cleaning solution and see what happens.
        Your fuel trim levels could be outta wack also and dumping in more fuel than necessary if your rear O2 is coded out and you haven't resistored the N80 properly and coded it out specifically. (your uni stg1+ won't have this unless specifically requested and paying for it usually)

        In reference i have the Gonzo tune and got them tuned out accordingly and get ~600km/tank typically in the city and more on the highway
        Looks like I used recharge incorrectly. I have a dryflow filter.
        Maf is brand new.
        O2 sensors are coded out properly with Unitronic Stage 2
        I used plug and play resistors from Urotuning for all deletes...could be possible I have a bad one....which sucks cause I just sold the 3 extra ones I had! haha
        Bagged 2004 Jetta GLS 1.8T Stage 2 Unitronic, 2016 Tiguan R-Line , S13 SR20DET, Mk2 VR6 Project, 2011 Dodge Ram 1500

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        • #5
          Re: Poor fuel economy 1.8T

          Originally posted by jaysleeves View Post
          Looks like I used recharge incorrectly. I have a dryflow filter.
          Maf is brand new.
          O2 sensors are coded out properly with Unitronic Stage 2
          I used plug and play resistors from Urotuning for all deletes...could be possible I have a bad one....which sucks cause I just sold the 3 extra ones I had! haha
          Is the engine running ok or does it seem to bog down at all? Like does it seem like it is getting too much fuel

          Originally posted by onceover View Post
          Could be worth putting in a new primary O2 sensor too. They do wear out eventually and give poor economy.

          Sean, the rear O2 sensor has no effect on how the engine runs, its merely there to ensure the cat is working properly
          Right my bad. I agree a primary O2 could be giving incorrect readings and give poor economy

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          • #6
            Re: Poor fuel economy 1.8T

            My GTI had this same problem. That thing was an absolute pig on fuel. Part of ot was the humongous injectors that were on it but those got swapped out and still had poor fuel economy.
            Evan

            Brilliant Black B6 A4 1.8T

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            • #7
              Re: Poor fuel economy 1.8T

              Originally posted by MechEngg View Post
              Is the engine running ok or does it seem to bog down at all? Like does it seem like it is getting too much fuel
              runs fine as far as I can tell....maybe this has something to do with my low dyno numbers too (175hp at the wheels)
              Bagged 2004 Jetta GLS 1.8T Stage 2 Unitronic, 2016 Tiguan R-Line , S13 SR20DET, Mk2 VR6 Project, 2011 Dodge Ram 1500

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              • #8
                Re: Poor fuel economy 1.8T

                Well.. I'm driving a vr6 like I stole it every day and average 400 per tank so I think your jetta had a little bit of problem to start with.
                This may sound a little strange but my BMW had a very leaky fuel line, and i did about 175km before it ran out, I couldn't figure out the issue because gasoline evaporates on the ground, i fixed the leak and 450+ per tank easily. I suspect you have a bad fuel leak somewhere in the system, a clogged maf or o2 sensor shouldn't make it that bad.
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                • #9
                  Re: Poor fuel economy 1.8T

                  Originally posted by kujiwara View Post
                  Well.. I'm driving a vr6 like I stole it every day and average 400 per tank so I think your jetta had a little bit of problem to start with.
                  This may sound a little strange but my BMW had a very leaky fuel line, and i did about 175km before it ran out, I couldn't figure out the issue because gasoline evaporates on the ground, i fixed the leak and 450+ per tank easily. I suspect you have a bad fuel leak somewhere in the system, a clogged maf or o2 sensor shouldn't make it that bad.
                  If you have a leak that affects your mileage that badly wouldn't you have quite a strong smell of gas around and inside the car?? I had a leak and it was pretty bad inside the cabin...
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                  • #10
                    Re: Poor fuel economy 1.8T

                    If you can get a hold of vcds you can log blocks 30, 31, 32 (or something along those lines) and you can see if you fuel trims are adapting. Also check block 99 to see if o2 regulation is turned on.

                    If any of those show negative results it's likely a bad resistor or a wiring issue. If not, it's most likely one of the issues others have mentioned
                    Dylan

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                    • #11
                      Re: Poor fuel economy 1.8T

                      Id start as Dylan said and get some logging done, something is defiantly up with the mileage and the dyno.
                      I still get like 400 to a tank with 830cc injectors
                      Do you know what you're afr is like at part throttle ?
                      Derek
                      01 GTI -cammed+stroked
                      06 gmc - duramax
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                      • #12
                        Re: Poor fuel economy 1.8T

                        Originally posted by Ur0Drivr View Post
                        If you have a leak that affects your mileage that badly wouldn't you have quite a strong smell of gas around and inside the car?? I had a leak and it was pretty bad inside the cabin...
                        Nope, I never paid attention.
                        Current Fleet
                        #ProjectICreate Jetta GLI32
                        2001 Cobra #88/3786
                        1989 Jetta Trophy 1 of 500
                        2004 Audi A2 FSI Colour Storm RHD
                        2015 B8.5 S4 Sepang/Technik/6MT/SD/AAD/CF

                        Motorsport Engineer

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                        • #13
                          Re: Poor fuel economy 1.8T

                          I think 450 in the city is about normal for a 1.8T....my 2.0L was about 600/tank in the city.....can't see it being a leak.

                          I need vagcom!
                          Bagged 2004 Jetta GLS 1.8T Stage 2 Unitronic, 2016 Tiguan R-Line , S13 SR20DET, Mk2 VR6 Project, 2011 Dodge Ram 1500

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                          • #14
                            Re: Poor fuel economy 1.8T

                            I get 600 km to a tank Unitronic 1.5 tune ... And that was with a bad o2 sensor, don't think I've ever got worse then 500 km in city driving in winter
                            12 Volvo XC 90
                            03 Jetta1.8T
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                            Colleen at 403-819-0132 or colleen@brayco.ca for all your mortgage needs.

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                            • #15
                              Re: Poor fuel economy 1.8T

                              interesting!


                              so who's got vagcom and wants to come give me a scan?!
                              Bagged 2004 Jetta GLS 1.8T Stage 2 Unitronic, 2016 Tiguan R-Line , S13 SR20DET, Mk2 VR6 Project, 2011 Dodge Ram 1500

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