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Cruize control

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sammy, Dec 12, 2000.

  1. Sammy

    Sammy 1/2 ton status

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    Can anyone tell me about the cruize control system. Where is the control system, where is the speed sensor, what are the most commen problems. I've got workshop manuals but none have anything about the cruize control. Mine on my 1988 K5 Grand GT is dead. It does not do anything anymore. And yes I've checked the fuses.

    Sammy.
     
  2. rich'90

    rich'90 1/2 ton status

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    check your vacuum lines, that is how it is controlled. and i believe your speed sensor is on the transmission. not sure on that one someone here can correct me. it may be behind the dash conected to your speedometer.
    good luck
    rich

    Go heavy or Go home[​IMG]
     
  3. jarheadk5

    jarheadk5 1/2 ton status

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    My 87's didn't work either, checked fuses and lines, all good. I found that the linkage between the vacuum servo and the throttle body was gone. So I cobbled a linkage together with coat-hanger wire and a little piece of scrap aluminum, and now it works OK. It won't accelerate or resume (probably wiring problems), but it will hold the speed I set it at, and that's all I really need.

    [​IMG] Semper Maintenance!
     
  4. Blue85

    Blue85 Troll Premium Member

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    I can tell you how it works on an '85, I think that it is the same for '88, but with the PCM, there may be some differences. The speed sensor is in the speedometer. It uses an IR emitter and detector pair to count the number of revolutions that the little "U"-shaped piece turns. This piece turns at the same speed as the speedometer cable. This is connected to the cruise module, along with the steering column controls, the valve and the power. The vacuum servo is actually controlled by an electric valve. The cruise module opens and closes that valve in order to control the amount of vacuum reaching the servo and therefore the throttle position and eventually speed. So it is a closed-loop system with several intermediate steps. This is necessary since the amount of vacuum can vary so much depending on the engine load (from hills and so forth). There is an adjustable linkage from the vacuum servo to the throttle lever on the carb for mine. If you have the same setup, you will see this great big vacuum servo with a linkage to the throttle body.

    It is possible, however, that your cruise is not vacuum operated and that the VSS signal to the ECM is used for speed. It would also be likely then that the control of the throttle body is done with an electric actuator. The real question is whether or not you have a cruise control module or if the cruise function is done by the ECM. Can someone else answer this?

    "If it aint broke...Make it work better!"
     
  5. jarheadk5

    jarheadk5 1/2 ton status

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    I would think that if the cruise is all ECM, there wouldn't be that big vacuum servo right behind the throttle body. SO, if you don't see a black rubbery/plastic-looking cylinder about 3" or so in diameter, the cruise is electronic, and I can't help you there...

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