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    Fuel Pump stays on & hesitation under load and idle

    Hi all, I'm having two issues with my 1991 Crown Vic 5.0L.

    1.) The car hesitates under throttle and can sometimes stall out. Feels like a misfire of some sort. Its worth noting I didn't start experiencing these issues until I had the catalytic converter, fuel pump, fuel filter, and smog pump replaced. So I'm not sure if its a related issue or not? I have since replaced the EGR, MAP sensor, vacuum lines under plenum, ignition control module, throttle position sensor, and plugs/wires with no luck.

    2.) As of recent the fuel pump stays on after the cars been turned off that the ignition key removed. Would this be a fuel pump relay issue? If so does anyone know where its located? Thanks for any tips, this cars driving me nuts as of late lol

    #2
    #2 sounds like a sticking fuel pump relay. Not sure on the 91's but on the slightly older ones, it is located on the driver's side fender wall close to the front (along with the A/C and horn relays). Could research it but someone here is going to tell us anyway.
    What I Own: 1993 Mercury Grand Marquis GS
    What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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      #3
      Found fuel relay, thanks

      Comment


        #4
        Originally posted by Hill185 View Post
        Found fuel relay, thanks
        Was it where I said or elsewhere?
        What I Own: 1993 Mercury Grand Marquis GS
        What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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          #5
          On drivers side atop wheel-well with ECU relay

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            #6
            Originally posted by Hill185 View Post
            On drivers side atop wheel-well with ECU relay
            Great - swap that out and see what happens. I guess they still have the 3 relays there - Fuel Pump, ECU, A/C and the Horn relay in under there as well.
            What I Own: 1993 Mercury Grand Marquis GS
            What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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              #7
              yeah that started in 1990. The little box will slide up out of it's mount, then the cover slides off to access the relays.

              For the misfire problem, check the vacuum lines around the smog pump. Should be one semi-large one running down that way from the cruise control stuff, and a couple of small ones. If those have melted off you may have a vacuum leak issue.
              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

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                #8
                Thank you Gadget, ill check double check the vacuum lines. Is it possible the aftermarket catalytic converter is causing the issue?

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                  #9
                  I never had any issue with the high flow cats I used on my 88 or my 93. Shouldn't be an issue unless there's a bad seal to the exhaust manifolds and the O2 sensor is reading external air causing it to run rich.

                  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.

                  Comment


                    #10
                    extremely unlikely. The ECM doesn't know or care if there is a converter there or not. If the oxygen sensor harness got melted it won't like that very much though.
                    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
                      1. Fuel Pump: So I changed relay in the fuel pump, however it continues to stay on unless I disconnect the battery. Even if I pull the relay completely out, the fuel pump will stay on with the key off car off. Extremely odd.

                      2. As far as vacuum lines everything seems normal and connected properly. I will say when I checked
                      the smog pump on my other 1991 that runs well, it had a different smog pump outlet. The one circled in red looks like it has outlet that’s not hooked up?

                      The picture circled in yellow is the smog pump in my other 1991 that runs good, and doesn’t have the additional “outlet”.

                      Click image for larger version

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                      Click image for larger version

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                      Last edited by Hill185; 10-10-2022, 03:23 PM.

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                        #12
                        Must then be a constant voltage to the fuel pump. Time to chase down the wiring issue.
                        What I Own: 1993 Mercury Grand Marquis GS
                        What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                        Comment


                          #13
                          Does it stop if you pull the relay?

                          The relay is pulled when power is applied to the two small pins. The + side comes from the ECM relay, so it is hot at all times when the key is on. The relay is actually switched on the ground side. That wire goes to the ECM, and it also goes to the self-test connector. Grounding the proper pin in the self test connector will force the pump on, a short in the wire will do the same. Its not a long run of wire so it shouldn't be difficult to check for damage.

                          The only other thing that does it is if the ECM is brain dead, but if the engine runs basically normally I have my doubts that its the ECM. Can always unplug it to see. Also maybe worth trying to pull codes. If it gives you a whole lot of odd codes, maybe it is the ECM.


                          The smog pump thing is tied into the cruise control system. Its not important and doesn't need to be there, though if the line is broken it can create a vac leak. Doesn't look like yours ever had a connection though, so unless there is a random decent size vacuum hose hanging out over there somewhere I don't think thats an issue. There is a vac line for the fuel vapor canister that lives under the battery. It runs sort of near the AC belt. I've had that slice open before. In your second pic I see it in split loom tubing. Not sure if its the same thing in the split loom in the first pic, but if it is that looks fine.

                          There are also normally a couple of small plastic lines tied into the smog pump controls.
                          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


                            #14
                            Thanks Gadget for your input. Yes if I pull out the fuel relay, the fuel pump will still continue to run. Since its been running poorly, (stalling, chugging, running rough) I recently replaced the ignition control module (ICM) and thought maybe it was the new ICM causing the fuel pump to continually run, however, I unplugged the harness to ICM with no change. You have me worried now the ECM is damaged. Ill check the grounds and wires like you mentioned next. Thank you

                            Comment


                              #15
                              Originally posted by friskyfrankie View Post
                              Must then be a constant voltage to the fuel pump. Time to chase down the wiring issue.
                              +1!
                              What I Own: 1993 Mercury Grand Marquis GS
                              What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

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