Cruise control on 85 FWB
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Cruise control on 85 FWB in Past Cadillac Vehicle Discussion; I went went on a trip to the beach with the family: The cruise control worked great for most of ...
  1. #1
    j2rossit is offline Cadillac Owners Enthusiast
    Automobile(s): 85 FW Brougham, 68 Buick Wildcat Convertible 455 4bbl
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    Cruise control on 85 FWB

    I went went on a trip to the beach with the family:
    The cruise control worked great for most of the trip but during the last few minutes of the drive, it went haywire. I had changed my speed and re-set the cruise when all of a sudden instead of applying a smooth light throttle to maintain speed, it started surging and I could feel the pedal bouncing back and forth from full throttle to no throttle. after a couple pulses I smelled the smell of electronics getting hot.
    So I shut the cruise off and finished the trip.
    On the way home, the cruise was working fine again for the first 45 minutes and then started again. I also notice that the speedo needle started shaking when it happened (it usually is pretty steady). after a minute or so, the speedo needle settled down and stoped shaking and so I tried the cruise, all was good with the cruise again. I stopped using the cruise and noticed that every once in a while the speedo would shake for a minute or so and then smooth out, (it was still reading the right speed, just shaking). I'm thinking that there is something that might be going with my VSS which is screwing with the cruise and the needle at the same time.
    Anyone ever heard of anything like this?

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  3. #2
    Jeppi94's Avatar
    Jeppi94 is offline Cadillac Owners Member
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    Re: Cruise control on 85 FWB

    Maybe there's something wrong with the Vacuum bottle for the Cruise Control, i've never experience problems with mine, but the previous owner of my car had it replaced

  4. #3
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Cruise control on 85 FWB

    After pouring over the FSM and talking with some friends, I've learned that the VSS doesn't control the needle, instead the speedo cable runs all the way down to the transmission. Therefore the shaking needle is most likely caused by the cable needing to be re-lubricated. This shaking would quite likely confuse the ECM since the VSS which reads it's value from the speedo cable is at the speedo head in the dash. I'm going to start by re-lubing the cable and see where that leaves the Cruise.

    Thanks Jeppi for bouncing the idea. The reason I doubt it's a vacuum problem is that when the speed drops, the throttle comes on full strength just fine until the car reaches the set speed. The problem only seems to occur when it's trying to maintain speed requiring light throttle.

  5. #4
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Cruise control on 85 FWB

    You should also check is the speedometer driven gear for any chips or signs of wear (the driven gear is located at the rear of the transmission). Also check the the throttle valve and T.V. cable, which runs from the carburettor to the transmission.

    Vacuum leaks can cause the speedometer to fluctuate, and vacuum leaks will cause the CC Servo to malfunction. Being that it's not happening constantly, there may be a leak to something that only draws vacuum under certain driving conditions (such as the EGR, ILC, or Canister Purge). The vent valve on the CC Servo (the smaller diameter vacuum hose) may also be defective, and slowly cause vacuum loss (forcing the vehicle to surge with the Cruise Control engaged).

  6. #5
    Robin Banx's Avatar
    Robin Banx is offline Cadillac Owners Fanatic
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    Re: Cruise control on 85 FWB

    ^^ Nice to see Sven chiming in here again. We've missed him. Welcome back young man.

    Cheers...........R.

  7. #6
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: Cruise control on 85 FWB

    I'll chime in with an issue, too. I've posted this one before, but never sorted it out (because mom doesn't like/use cruise).

    On mom's 84 FWB, the cruise stopped working a few years ago. Green light comes on with the switch, but when I hit the button on the stalk, the yellow light comes on momentarily, then goes out. Cruise does not engage. I'm thinking a bad vacuum line, but I'm open to ideas. I suppose I should go drag the FSM off the shelf.

  8. #7
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Cruise control on 85 FWB

    I have a GM Cruise Control Manual, and it's difficult to understand which system was installed in which vehicles (it seems the carburetted Cadillacs have a combination of two entirely different systems).

    The manual indicates that all Cadillac models that had Digital Fuel Injection, used a DFI cruise control system in 1984 (and presumably in '85 as well).The manual also lists several trouble codes, starting with 60 and ending with 71, but it doesn't say if these codes can be accessed through the vehicle's on-board diagnostic system or even what section they would be under. The manual doesn't provide any explanation as to what the indicator lights mean.

    My factory service manual, for my '89, which uses a DFI control switch and what I believe is and AC DELCO Custom Cruise III CC Servo, says that the amber light illuminates to show that the system is in standby (may be engaged at anytime) and the green light illuminates to show that the system is on (the button on the stalk has been pressed). The lights on yours may be reversed from mine, but the one that comes on when the switch is engaged should be next to "Cruise Control" and the light next to "On-Auto" should come on when the engage switch is pressed.

    Looking at the wiring diagram, there could be a damage wire between the engage switch or the brake switch, and the CC control module. Connection to the brake switch is a determining factor in the engagement of the CC system, so that's where I would look first; the wire could be loose, or the switch itself may be partially engaged. You should also check the connector to the module, to see if the prongs are corroded or loose.

  9. #8
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Cruise control on 85 FWB

    Jay, I had that same issue on mine last year as well as my buddy with his 82. It was solved for both of us by finding some vacuum lines that had fallen off (I think mine was under the air cleaner, but can't remember where his was. when the vacuum lines were re-connected, the green light would stay on and all was good after that. Until my current problem.
    There are several trouble codes that are linked with the cruise system that might be present.

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