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    Gas gauge

    My gas gauge is inaccurate, at less than 1/8th of a tank it only takes 12.7 gallons to fill it. It also drops when I start the car a little bit and sometimes goes up a little bit when im driving.

    I know that the in-tank sending units are notorious for going bad, but could it be something else? Its an inconsistent problem and the car runs better when it doesn't have problems.
    Current rides - 1991 Ford Thunderbird 3.8 v6 (gas saver/DD) - New Heads/Headgaskets with ARP studs, Air Silencer Delete, 70mm MAF, Plasti-dipped Matte Black with a Silver Metalflake Overlay, Muffler Delete, some LED's, 30.233 MPG for high MPG average!
    2006 Jeep Wrangler 4WD (fun vehicle/backup DD) - 4.0/6spd - too many mods to list.

    Associated Panthers:
    Father's 1994 Ford Crown Victoria - Stock, 45,000 miles.
    Sold in 2007 - 1987 Mercury Grand Marquis LS "Grandpa Special" 2 door.
    http://www.cardomain.com/ride/2128327

    #2
    My car does something similar, it takes about 12 gallons to fill up from 1/8 tank. That's alos about when the light comes on. Thinking of it I've never had to put more than 15 gallons in it, and that's with the indicator pointing at "E". It's really consistent though, the only indicator fluctuation I get is when I start going up or down some hill. But I mostly trust the odometer - 150 miles from last fill-up and I start looking for the cheapest gas around, when it hits 200 miles it's high time I take the trip to the pump.

    Comment


      #3
      sounds like bad grounds making the guage float. Pull and clean the battery connections, the connections at the starter relay, the ground cable to the engine, the engine to body strap, and the ground(s) on the fuel tank. You'd be surprised what kind of stupid problems that fixes.

      Guages in these cars are way the hell off. 1/2 tank is about 10.5-11 gallons in an 18 gallon tank. 3/4 tank is 7 gallons. I get roughly 3 gallons beyond the F mark till its really full. They skew these things so it takes longer to go from full to 1/2 than it does to go from 1/2 to E. Its an illusion to make you think you're getting better fuel economy. People think "golly, I'm at 1/2 tank and i've gone 200 miles. This thing must be good for 400 to a tank!" when really its good for maybe 275-300.
      86 Lincoln Town Car (Galactica).
      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

      91 Lincoln Mark VII LSC grandpa spec white and cranberry

      1984 Lincoln Continental TurboDiesel - rolls coal

      Originally posted by phayzer5
      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

      Comment


        #4
        I'll agree on these car's gas gauges. It's a guessing game on how much fuel you actually have. The float on the sending unit could be on it's way out. But I'd check all those grounds and connections like gadget73 said.

        I don't know if these cars have an instrument voltage regulator, but that could be to blame for the variation before and after start up. I think mine is on the way out, the gauge moves back and forth while the car is sitting still! If it goes completely bad, the gas gauge will peg (as would all the other gauges if Ford had put anymore).
        1990 Country Squire - weekend cruiser, next project
        1988 Crown Vic LTD Wagon - waiting in the wings

        GMN Box Panther History
        Box Panther Horsepower and Torque Ratings
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        Comment


          #5
          There is an instrument voltage regulator buried in the dash somewhere, should be putting out ~5vdc. Depends how the thing fails tho, it might peg full, or it might show empty. If it pegs full, its probably shorted to ground. Empty is an open circuit.
          86 Lincoln Town Car (Galactica).
          5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

          91 Lincoln Mark VII LSC grandpa spec white and cranberry

          1984 Lincoln Continental TurboDiesel - rolls coal

          Originally posted by phayzer5
          I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

          Comment


            #6
            Originally posted by gadget73
            sounds like bad grounds making the guage float. Pull and clean the battery connections, the connections at the starter relay, the ground cable to the engine, the engine to body strap, and the ground(s) on the fuel tank. You'd be surprised what kind of stupid problems that fixes.

            Guages in these cars are way the hell off. 1/2 tank is about 10.5-11 gallons in an 18 gallon tank. 3/4 tank is 7 gallons. I get roughly 3 gallons beyond the F mark till its really full. They skew these things so it takes longer to go from full to 1/2 than it does to go from 1/2 to E. Its an illusion to make you think you're getting better fuel economy. People think "golly, I'm at 1/2 tank and i've gone 200 miles. This thing must be good for 400 to a tank!" when really its good for maybe 275-300.
            I've noticed the same thing, my fuel economy goes to shit after a half a tank, while before then its possible to get 170-200 miles to a half of tank. I allways thought it was something else causing worse fuel economy after a half of tank (sludge buildup in the tank), but that makes more sense since I've cleaned out the fuel system several times.

            I'll check the grounds, I think I might have a loose connection somewhere since I've been having some other electrical problems. I've been having problems with both windows sometimes (get stuck or work like the battery is dying) and their is some noise coming through the radio.
            Current rides - 1991 Ford Thunderbird 3.8 v6 (gas saver/DD) - New Heads/Headgaskets with ARP studs, Air Silencer Delete, 70mm MAF, Plasti-dipped Matte Black with a Silver Metalflake Overlay, Muffler Delete, some LED's, 30.233 MPG for high MPG average!
            2006 Jeep Wrangler 4WD (fun vehicle/backup DD) - 4.0/6spd - too many mods to list.

            Associated Panthers:
            Father's 1994 Ford Crown Victoria - Stock, 45,000 miles.
            Sold in 2007 - 1987 Mercury Grand Marquis LS "Grandpa Special" 2 door.
            http://www.cardomain.com/ride/2128327

            Comment


              #7
              Both my fuel gauge and my water temp gauge like to wander around, the water temp needle will go all the way over to hot, then wander back down to where it was before, does it at the same time as the gas gauge. Something is screwy in there somewhere
              Pebbles-1968 Ford F250
              Pile of Junk! An Electronics Project Site (To get wet by)<---Clicky! NEW STUFF!!!!

              Comment


                #8
                there is an NOS fuel guage on ebay for cheap... Id jump on it if that may be the problem.
                Pete ::::>>> resident LED addict and CFI defector LED bulb replacements
                'LTD HPP' 85 Vic (my rusty baby) '06 Honda Reflex 250cc 'Baileys' 91 Vic (faded cream puff) ClifFord 'ODB' 88 P72 (SOLD) '77 LTDII (RIP)
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                85HPP's most noteworthy mods: CFI to SEFI conversion w/HO upperstuff headers & flowmasters P71 airbox Towncar seats LED dash light-show center console w/5 gauge package LED 3rd brake light 3G alternator mini starter washer/coolant bottle upgrade Towncar power trunk pull underhood fuse/relay box 16" HPP wheels - police swaybars w/poly rubbers - budget Alpine driven 10 speaker stereo

                Comment


                  #9
                  Don't know if it is, for some reason if you turn the key to ignition and let the fuel pump prime the injectors before starting it, it reads correctly. However, as soon as you start the car it goes down a half of quarter or more and floats.

                  Im going to take a look at it tommorow, got a link for the fuel gauge?
                  Current rides - 1991 Ford Thunderbird 3.8 v6 (gas saver/DD) - New Heads/Headgaskets with ARP studs, Air Silencer Delete, 70mm MAF, Plasti-dipped Matte Black with a Silver Metalflake Overlay, Muffler Delete, some LED's, 30.233 MPG for high MPG average!
                  2006 Jeep Wrangler 4WD (fun vehicle/backup DD) - 4.0/6spd - too many mods to list.

                  Associated Panthers:
                  Father's 1994 Ford Crown Victoria - Stock, 45,000 miles.
                  Sold in 2007 - 1987 Mercury Grand Marquis LS "Grandpa Special" 2 door.
                  http://www.cardomain.com/ride/2128327

                  Comment


                    #10
                    I'm betting on bad grounds to the engine and body. Floating guages and flickering lights and other crap like that are very common symptoms of a bad connection.
                    86 Lincoln Town Car (Galactica).
                    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                    91 Lincoln Mark VII LSC grandpa spec white and cranberry

                    1984 Lincoln Continental TurboDiesel - rolls coal

                    Originally posted by phayzer5
                    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                    Comment


                      #11
                      I fixed some of the grounds and added new ones also since it seemed to help out alot. This was only in the engine compartment, I haven't checked under the car yet. The head lights are brighter and don't flicker, the radio is clear-sounding, and it seems to run a little smoother. It didn't fix the gauge though, it still floats and now reads a quarter low even with the tank full. It just drops as soon as you start it, so I'm guessing the sending unit is probably bad.
                      Current rides - 1991 Ford Thunderbird 3.8 v6 (gas saver/DD) - New Heads/Headgaskets with ARP studs, Air Silencer Delete, 70mm MAF, Plasti-dipped Matte Black with a Silver Metalflake Overlay, Muffler Delete, some LED's, 30.233 MPG for high MPG average!
                      2006 Jeep Wrangler 4WD (fun vehicle/backup DD) - 4.0/6spd - too many mods to list.

                      Associated Panthers:
                      Father's 1994 Ford Crown Victoria - Stock, 45,000 miles.
                      Sold in 2007 - 1987 Mercury Grand Marquis LS "Grandpa Special" 2 door.
                      http://www.cardomain.com/ride/2128327

                      Comment

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