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How to get better fuel economy out of CFI?

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    #1

    How to get better fuel economy out of CFI?

    On my 85 Gm I've been averaging around 11 mpg, and I'm reading about people on this forum making around 20 lol. So far I've completely removed the egr, smog pump, and catalytic converter systems and installed a 12" glasspack in place of the factory muffler and also a new timing set, and fresh tune up

    what mods can I do to get better gas mileage out of this thing?
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    #2
    Keep your foot out of it. The easiest way to get better mileage is to not floor it. With all those mods and maintenance, it should be in top shape. You should be getting at least 16-17 mpg in the city. The trans may need adjusted or rebuilt.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.

    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

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      #3
      Originally posted by sly View Post
      Keep your foot out of it. The easiest way to get better mileage is to not floor it. With all those mods and maintenance, it should be in top shape. You should be getting at least 16-17 mpg in the city. The trans may need adjusted or rebuilt.
      My spark plugs were pretty carboned up when I replaced them, do you think cleaning the o2 sensor would do anything?

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        #4
        I would always start with a though check of the electrical system (battery, alternator, cables, grounds) and then do a complete tune up (plugs, filters (gas and air), plug wires, cap and rotor). Then see how things go.
        What I Own: 1993 Mercury Grand Marquis GS
        What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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          #5
          How old is the O2 sensor?
          These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.

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            #6
            My 79 CS had a seized EGR valve that was causing a bad smell in the cabin. I replaced it with a decent used one and my mpg went from 12.3 to 14 (Imperial gallons so YMMV).
            An egr system that is functioning correctly will increase fuel economy. A lot of people thing deleting it will improve performance but at a cost od fuel economy.
            I would leave off everything you deleted EXCEPT the egr and see if that helps.
            • Likes 1

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              #7
              +1 keep the EGR functioning.
              You probably shouldn't expect to hit 20mpg, these cars are so old that individual experiences vary alot. My CFI never got better than 16 mpg, but something must've been wrong with it. Like with anything else, fresh tuneup will get your MPG where it should be, as long as something isn't wrong.
              If you're looking for modifications, an exhaust larger than the factory single 2" pipe will probably help some. Your rear end gear ratio also effects cruising MPG quite a bit.
              1985 Mercury Grand Marquis LS, "Maisa"
              2005 Volvo V70 Bi-Fuel

              Comment

                #8
                Originally posted by ianmcc View Post
                My 79 CS had a seized EGR valve that was causing a bad smell in the cabin. I replaced it with a decent used one and my mpg went from 12.3 to 14 (Imperial gallons so YMMV).
                An egr system that is functioning correctly will increase fuel economy. A lot of people thing deleting it will improve performance but at a cost od fuel economy.
                I would leave off everything you deleted EXCEPT the egr and see if that helps.
                The bad part is that I think all my egr parts are long gone by now

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                  #9
                  Originally posted by 91merc View Post

                  The bad part is that I think all my egr parts are long gone by now
                  Good part is they should be readily available.
                  What I Own: 1993 Mercury Grand Marquis GS
                  What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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                    #10
                    I used a junkyard unit from a 351W Ford truck. As long as it holds vacuum and moves under load and bolts up to the manifold you should be good.

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                      #11
                      replace the O2 sensor if its old. I remember working on an 84 with Scott, the fuel economy was terrible. Pulled the O2 sensor and did the check with the propane torch, it did nothing. New sensor and it went from low teens to near 20 mpg. It had previously been tuned up, vac leaks fixed,timing chain, etc. It honestly didn't run any different, other than eating a lot of extra fuel.
                      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
                      • Likes 1

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                        #12
                        Well I think I figured out that walmart gas was the culprit, I've switched to using shell gas and last tank I was getting around 16mpg as opposed to the 11mpg I was making beforehand

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                          #13
                          Originally posted by 91merc View Post
                          Well I think I figured out that walmart gas was the culprit, I've switched to using shell gas and last tank I was getting around 16mpg as opposed to the 11mpg I was making beforehand
                          Might want to check and see if both stations have the same amount of ethanol in their blends. That might be an issue.
                          What I Own: 1993 Mercury Grand Marquis GS
                          What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                          Comment

                            #14
                            Hopefully switching gas and getting better mileage will make my 35 mile commute a little easier on the wallet lol

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                              #15
                              thats a pretty big difference just from switching gas. More than ethanol should explain
                              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

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