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    Cruise control doesn’t work

    Is there any way to diagnose this system? All fuses are good and it doesn’t throw a vss code so my guess would be either the servo or transducer but how could I test either one?


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    #2
    on what? the 87? VSS doesn't actually connect to the ECM in 87 so you won't get a code for that. If you have a tripminder that works, that proves the VSS works.

    does the horn work? Cruise buttons are powered through the horn relay so if thats dead the CC will be too
    do you have LED tail lights? Gets dumb if you do
    beyond that check the vacuum dump valve above the brake pedal. Easy way is to unplug it at the cruise servo to see if it holds vacuum. If you look on the servo you'll see a short hose that goes from one side of the can to the other with a Y connector going off someplace else. Thats the vac dump line. If that does not hold vacuum the CC will not function.
    also make sure you actually have vacuum supply to the servo, and that the cable from the throttle body to the servo is not broken internally.
    also make sure the tail lights work as expected. If the brake light switch failed and the brake lights are stuck on, the CC will not work.

    There are more detailed diag processes in the manuals but those are the easy and likely things for it to be. Personally I've had more issues with vacuum dump valves than anything else. usually just out of position after working on something under the dashboard.
    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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      #3
      I second the vacuum dump valve. Many of the cruise/speed control modules have labels for the wiring connections so you can figure out what goes where pretty easily.
      Also make sure the connectors are tight on the controller itself; they aren't the stoutest connectors out there.

      Gadget, I think the VSS connection on EEC-IV is used to prove the car isn't coasting (coasting is a different condition from sitting still in neutral or drive) so the computer knows it can pull fuel but not go to full idle mode. I'll have to look that up, though, now that I'm thinking about it.

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        #4
        I’m sorry yes its for my 87. Its a gs so no tripminder too. No leds, brake light switch and horn work. I’ll check the dump valve when I can, thanks. I bet thats the issue as it seems everything else is fine but with the car being 33 years old I’m sure the diaphram in the servo is leaking.


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          #5
          haven't had that, but unless the diaphragm is completely ripped it would still work even with a leak. Might surge tho. Leaky vac dump valve does the same thing. If its not holding at all though it flat out won't work.


          as for the vss, I know 86 has no vss connection to the ECM, pretty sure 87 didn't either. I had to add those pins on my 86 when I converted it to mass air in order for the EGR to behave itself.
          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
            The dump valve is where exactly?


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              #7
              Im subbing this thread, my cc worked a couple times and stopped.
              The shaft broke later though, so the fix won't be as simple.

              Is the cfi cruise setup similar to the efi one?
              1985 Mercury Grand Marquis LS, "Maisa"
              1995 Chevrolet Caprice Classic STW, "Sally"

              Comment


                #8
                Originally posted by 87GrandMarq View Post
                The dump valve is where exactly?


                Sent from my iPhone using Tapatalk
                They are talking about the dump valve directly above the brake pedal...above steering shaft..shitty area to access.

                It has a large vacuum line going to it.

                If you follow the brake pedal pad upward its brake pedal lever you will see a white (should be white) piece of plastic next to the brake light switch. that white piece of plastic makes contact with the dump valve in question. The dump valve threads into a hanger. It has a plunger that releases vacuum from the servo mounted under the hood on the drivers side inner fender once the brake pedal is applied. Brake pedal not applied the plunger is closed and vacuum is stored in the servo...I Believe that is the gist of it.
                ~David~

                My 1987 Crown Victoria Coupe: The Brown Blob
                My 2004 Mercedes Benz E320:The Benz

                Originally posted by ootdega
                My life is a long series of "nevermind" and "I guess not."

                Originally posted by DerekTheGreat
                But, that's just coming from me, this site's biggest pessimist. Best of luck

                Originally posted by gadget73
                my car starts and it has AC. Yours doesn't start and it has no AC. Seems obvious to me.




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                  #9
                  Oh ok I’ll take a look. There is something leaking under the dash but I thought it was the parking brake release, perhaps its not.


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                    #10
                    the dump valve only has vacuum on it when you engage the cruise control.
                    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
                      So if I were to engage it and not hear a hiss its probably electrical because its not getting vacuum?


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                        #12
                        No. There should be no hiss from the dump valve at all until you press the brake with cruise engaged and then only long enough to break the vacuum in the cruise solenoid. If you hear a hiss already near the floor, it will probably be the half moon shaped valve at the bottom of the steering shaft that actuates the parking brake release. The leak could also be coming from the actuator itself. Pull the black line off the valve on the steering shaft and plug/cap it and the leak should stop.

                        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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                          #13
                          just unhook it under the hood and pull vacuum on it. If it holds, that isn't your problem.
                          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
                            I can say that most times the cruise failed on me it was a vacuum leak.
                            03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
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                            08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
                            12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

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                              #15
                              Hmm ok I’ll do that tomorrow thanks for the tips.


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