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Cruise Control - Individual Component Troubleshooting

Discussion in 'Stock 1991 - 1994 Explorers' started by ChildIdencicant, November 14, 2018.

^^Searches ExplorerForum.com^^

  1. ChildIdencicant

    ChildIdencicant New Member

    January 14, 2016
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    1994 explorer
    Purpose of thread is to hopefully provide some troubleshooting advice in detail not otherwise yet available via this forum for 1st gen explorers. Approach to advice is made assuming that no other issues are present. I have no reccommendation as to the order in which components are tested (except make sure your brake lights work first), as circumstance can change reasoning for prioritizing a test. Example; cruise control worked before you had trans work done, but not after? check that vss & connection. Only works in the Heat/Cold but still reliably? Could be vacuum or electrical. etc.

    My vehicle:
    1994 2wd 4.0L Automatic
    Trans: A4LD
    170,000 miles

    Component: Vacuum Dump Valve
    Location: Drivers side, under the dash, mounted above a plastic shelf which is clipped on to the brake pedal. It is
    connected to a hose that goes through the firewall, connects to the cruise control servo. The "shelf" should
    be flat, and hold the valve in when the brake pedal is not pressed. If it is broken or bent, this can prevent
    the valve from properly closing. The distance between the valve and the shelf can be adjusted, and also fall
    out of adjustment, by pushing the valve itself up or down through its mounting retainer.

    Testing: Testing this part is most easily done from within the engine bay. Disconnect the hose from the servo , and
    connect it to a vacuum tester. Applying ≈ 15inHg is enough. The important part is that the vacuum is
    maintained. Apply the vacuum -wait 30 seconds to verify vacuum persistence - press brake pedal to dump
    vacuum. If vacuum persists, dump valve is good, move on. If the vacuum does not persist, and valve is
    verified to rest in closed position on its shelf, test the hose itself by removing the end connected to the valve
    and plugging it. If the vacuum persists, experimenting with dump valve depth might help, but replacement
    is most likely nevessary.

    Component: Speed Control Amplifier/ Cruise Control Amplifier
    Location: Multiple locations possible. Either under the dash, or behind the glove box. Mine was behind the glove box
    mounted with 2 t-25 torx head screws. Be very careful when removing the connectors. The plastic box has
    has gone through a lot of thermal cycling by now and is extremely brittle. Mine crumbled out in the back.

    Testing/Diagnosing: First things first. Ground yourself. Get rid of that nasty static charge. There is an IC in that box. Detailed troubleshooting here has to be limited, if for no other reason than I don't know what chip
    that is. I couldn't even identify the logo of the chip maker. All I know is its a DIP24 with pin 1 to
    ground. Second things second: check that trace and those joints. This is what actually turned out to
    be the problem for me. Visually inspecting each of the joints with a magnifying glass and checking
    continuity. Specifically I had a broken joint in the ground jumper. It was so minute that a change in
    air tempurature could make the system work again intermittently.
    Do you see it?
    1 down....
    There was also insufficient quantity of solder on some joints as well. If anything looks frosty, pitted, or cracked,
    just resolder it.

    The approach to make regarding actual component replacement here is to make the same assumptions as one would on similar electronics of similar age. Basically swap replace the electrolytic capacitors, and maybe the diode. That pot probably hasn't been adjusted since it was installed so it is still good but easy enough to test anyway, and unless you see scorch marks it is incredibly unlikely (in my experience) that one of the other basic components will be faulty. You must visually identify the values of that which you replace. I would not assume all of these amplifiers are the same .

    If you have something to add, do feel free to share. I will edit-add a section on troubleshooting the servo (solenoids, diaphram), steering wheel controls, and possibly VSS a little later.
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  3. roscoe 0202

    roscoe 0202 Active Member

    February 3, 2014
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    City, State:
    salt lake city utah
    Year, Model & Trim Level:
    1999 explorer sport
    thank you I believe my gem is at fault will get it out and check again thank you
  4. ExploreHudson

    ExploreHudson Member

    May 21, 2018
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    City, State:
    San Antonio, TX
    Year, Model & Trim Level:
    '91 Explorer Sport 2D
    Definitely want to look into this. Thank you for starting with some serious leg work
  5. AGodlyCanuck

    AGodlyCanuck Active Member

    June 13, 2018
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    City, State:
    Nelson, BC. Canada
    Year, Model & Trim Level:
    1992 Explorer 4dr 4x4 XLT
    I need to definitely try what you reccomend.
    Appreciate giving me a place to start ^~^

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