Drastically reduced fuel mileage

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  • Drastically reduced fuel mileage

    I ran about 6 tanks of fuel over the past week and my fuel mileage is way down. I have an 08 non ABS with just under 300,000 miles on it. I bought it 8 years ago new. I have consistently got 40 mpg until now. I think the lowest I've had was 38 mpg and the highest was 44 (when checked). But with quick math at fill ups I figure an average of 40 mpg for the life of my bike. This year the first 5 or 6 tanks the highest I've had was 34 mpg. Today was 2 tank fulls with 1 at 31 mpg and the other at 33. I didn't do anything different to my bike over the winter than any year before. Air filter, plugs, fork refresh, all fluids, etc. I did just have the brake recall done and the wheels seem to spin the same as they ever have. What would cause the sudden drop? The other day I turned my key on and I thought my fuel pump sounded louder than before, but that may have been my imagination, because now it seems ok. I'm glad gas prices are down, but I need to pull more than 150 to 170 miles from a tank of gas. I thought maybe it has something to do with the winter blend, but I've never had any problem before. The bike sounds and runs the same as it ever has. What would cause the drop? Thanks for any help.

  • #2
    Didn't you know that Honda has programmed the GL1800 to drop MPG by approximately 25% when you are approaching 300,000 mi. It's a marketing ploy to entice the owner into purchasing a new bike. I won't even tell you what will happen when you reach 325,000 mi.
    Other than this smart a$$ answer I really can't offer you any help.

    Location: Vancouver WA Former name: CAWING '04 GL1800
    When the power of love overcomes the love of power the world will know peace.
    Jimi Hendrix
    Vietnam Veteran, Patriot Guard Rider

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    • #3
      My 05 had a significant drop in fuel mileage and it turned out to be the fuel pressure regulator.
      I replaced the regulator and fuel mileage was back where it should be.

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      • #4
        Originally posted by jmohme View Post
        My 05 had a significant drop in fuel mileage and it turned out to be the fuel pressure regulator.
        I replaced the regulator and fuel mileage was back where it should be.
        I'm getting ready to pull the plugs and check them. How hard and how expensive is this FPR (fuel pressure regulator) you speak of? Thank you!

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        • #5
          I'm having the same issue; figure it's the winter fuel mixture.
          2008 Red GW1800 -- NRA Life Member - American Legion PUFL, American Legion Riders
          USMC 21 YRS/9 MO and when dead, a dead Marine.
          US Four Corner Ride https://clayusmcret.blogspot.com/
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          50th State ridden on 19 Aug, 2016 DS #1584

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          • #6
            I normally see a 10% drop during the winter. Your drop is not winter blend related. It is way to high. I would strongly suspect the O2 sensors. They can go bad and the ECM not throw a code. Those little buggers can be tricky that way. A bad O2 sensor can leave the bike running rich and make the mileage take a dump.
            [SIZE=12px][FONT=Arial]--Rob[/FONT][/SIZE]

            [SIZE=12px][FONT=Arial]'10 NT700VA (Wife's)
            '09 Metallic Silver GL18BM-Heli-MMTE[/FONT]
            [FONT=Arial]'89 CB1[/FONT][/SIZE]

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            • #7
              Originally posted by CAC View Post

              I'm getting ready to pull the plugs and check them. How hard and how expensive is this FPR (fuel pressure regulator) you speak of? Thank you!
              It has been two bikes ago, so I really don't remember the cost, but I don't recall it being an expensive part.
              It was a bit of a job to replace it, but not too bad. It is at the rear of the left fuel rail and did require removal of some plastic. If I recall it was the chrome piece above the valve comer and I had to remove the left side top shelter bolts and was able to pull the side of the fairing away enough to get to it.

              If you have a manual, it details the pressure check to determine if the regulator is bad.
              I would look it up for you, but I never replaced my manual after the fire.


              Originally posted by clayusmcret View Post
              I'm having the same issue; figure it's the winter fuel mixture.
              That is also a possibility.

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              • #8
                Another possibility with that kind of mileage is coil failure. Are any or all plugs wet fouled? That will be the #1way to isolate the problem. If all plugs are wet, it could be a sensor. If only sets of 2 are fouled, it would be spark related (coil and or wires). report back.

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                • #9
                  I was thinking maybe a fuel winter mix problem here too. Just put in new plugs maybe time for some injector cleaner.
                  2010 Pearl Yellow L3, Double Darksider #856, Ultimate Midrider Seat w Yellow inlays, F4+4 Tinted, Live To Ride, Love my Wing

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                  • #10
                    If you have an inspection camera take look to see if you have a riding buddy hitch hiking in your air filter.

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