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Speed Control Servo - how to check vacuum operation?

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    #1

    Speed Control Servo - how to check vacuum operation?

    Speed control doesn´t work on my 84 TC.

    How to check the servo motor for correct vacuum? Shop manual only tells how to check the electric circuit.
    I can get the actuator cable to retract by applying vacuum to the port that faces the front of the car (the short c-line is connected here)


    Steering wheel switches work
    Steering wheel brushes clean
    Wiring to amplifier ok
    Dump valve works and correctly adjusted (1,27mm shim to adaptor plate)
    Vac lines new
    Speed Sensor reads required 200ohms

    Still no cruise.
    Tags: None
    #2
    I’m having the exact same issue in my 87 mgm. I think it’s the servo itself. I’ll have to swap it out and see unless you figure it out before me.


    Sent from my iPhone using Tapatalk

    Comment

      #3
      pretty sure there is a test procedure in the factory manual, unless its in the EVTM. If the cable pulls when you apply vacuum manually, that part of it is good. The only other parts in there are the vacuum and vent solenoids, and a position sensor. if the position sensor is bad, the cruise will engage but the speed will vary wildly. Had a bad one on my Continental so I can tell you that from experience.

      Ohm check the run from the speed amp to the servo if you haven't yet. If any of that is open it won't work. 3 wires for the two solenoids, 3 more for the position sensor. If someone swapped the servo for an 88+ one, it will not have the sensor and it won't work correctly.

      also, you don't have LED brake lamps do you? If they aren't the kind with the internal resistors, it will keep the cruise from functioning. Its kind of a dumb device. It doesn't see +12v when you step on the brakes, it stops seeing ground through the bulbs. LEDs don't have the same low resistance that light bulbs do, so as far as the cruise module is concerned the brake pedal is pressed.

      did you verify the brake dump valve holds vacuum? You can check that from under the hood. If its wide open it won't work. if it has a slight leak it will engage but the speed will not hold stable.
      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
        ok its in the EVTM. This is from my 84 Conti book, but its the same system. Won't guarantee colors are not different in 87, but they probably are not.

        under "system does not operate"
        check for broken wires
        be sure throttle linkage moves freely
        cable from speed control servo must be as tight as possible without holding the throttle open

        -- side note, there is a clip that holds the stem of the cable to the "block" that clips it onto the throttle cable. If that metal clip is missing, it will not work. If you can pull vacuum manually on the servo and the engine speed increases, that clip is fine. If the adjustment is wrong it will just add some speed after you hit the "set" button, not a big deal.

        unplug connector from speed control amp[
        verify battery voltage at pink wire
        verify ground at black wire
        verify batt voltage at light blue / black when "ON" is pressed

        ohm meter between LB/BK and ground.
        Rotate wheel through full range and verify these resistance readings
        OFF - 0 to 1 ohm
        SET/ACCEL 646 - 714 ohms
        COAST - 114 - 126 ohms
        RESUME - 2090 - 2310 ohms

        check operation of vacuum dump valve - basically pull vacuum on it from under the hood and make sure it holds. Its the line on the Y splitter on the side of the servo that runs to the firewall
        check steering wheel brushes for 1 ohm or less (I'd think the resistance check above does that but I'm just telling you what the book says)

        read "speed control circuit diag" in group 37 of the shop manual, or watch some video coarse that I know you don't have and won't be able to find

        some stuff not in the book
        verify 50k ohms from brown / light green to pink / light blue on the connector from the speed control amp
        verify something between 0 and 50k from either BR/LG or PK/LB to yellow/red. You should get opposite readings here, one will be low and one will be high.

        from the shop manual
        unplug the speed control amp
        ohm from gray/black to orange/yellow. Should be 40 - 125 ohms
        ohm from white/pink to orange/yellow. Should be 60 - 190 ohms

        If those two resistance checks come out OK, the wiring between the speed control amp and the servo is good. If it fails, repeat those checks directly at the servo to figure out if the servo is bad or if its bad wiring.

        Functional test of the servo
        unplug speed control amp and start engine
        connect orange/yellow to battery +
        connect white/pink to ground
        touch grey/black to ground
        servo should pull in and engine speed will increase. Do not hold the wire to ground or it will go full throttle. Engine speed should hold steady.
        unhook white/pink from ground, engine should return to idle

        If that works, the servo is fine.
        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

          #5
          Solved!
          It was the brake switch wires.

          Previous owner had clipped both and ran two new wires to the stop lamps due to german law (turn signals MUST be amber - cannot be the stopligt blinking).
          Resoldered the light green wire to the brake switch connector - now I have cruise )

          Comment

            #6
            Nice.

            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

              #7
              Yes, much more comfortable to drive now.

              Comment

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