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Can you ID this GP controller

Discussion in '1982-Present GM Diesel' started by Mastiff, Feb 6, 2005.

  1. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I know everyone is into manual controllers around here, but I just want to get my existing setup cleaned up right now before I mess around. I'm trying to understand the wiring on my M1008, but it has a non-original GP controller. Can anyone tell what kind this is so I might look up the specs? I want to learn what the different connections are for. I'm also trying to figure out if this one uses coolant temp information or not, since I can't find any path to the existing CTS (it appears only to be wired to the factory GP controller, which is disabled).

    Anyway, here's the pic:

    [​IMG]
     
  2. 86dieselburb

    86dieselburb 1/2 ton status

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    That controller was used on 85-93 6.2's and 6.5's. If looking at it with the 4 wire connector at the top the wiring left to right goes like this.

    (A) ( B) (C) (D) (E)


    ( ) ( )

    pin A is open
    pin B comes from the ignition switch and gets engine cranking info from the starter.
    pin C glow plug sensor input and goes to the temperature inhibit switch
    pin D also comes from the ignition switch
    pin E is ground

    lower left connector is power to glow plugs
    lower right connector (blue wire in your photo) is batter power.

    If you give your email I can scan the schematic and email it to you.
     
  3. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Great, thanks. So I take it that this controller is just a timer basically, and doesn't do anything differently as a function of temperature (air or engine)?

    My E-mail is charles@taildragger.info.

    Thanks again.
     
  4. 86dieselburb

    86dieselburb 1/2 ton status

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    Well the controller does get engine temperature off the glow plug inhibit switch. At 125 degrees the inhibit switch switches off to prevent the glow plugs from operating above the 125 degrees mark. This controller you have takes the glow plug controller and relay of older systems and just combines into one unit. I assume the temperature inhibit switch is the same as used on older systems.
     
  5. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Thanks for sending the info. What does this inhibit switch look like? Also, when you say 125 degrees is that air temperature, coolant temp, or what? Based on the diagram, it looks like the inhibit switch simply opens the circuit at a certain temp, then the controller can sense this just so it knows. It wouldn't really have any other indication of temp besides knowing whether it is more or less than 125. Is that right?

    Sorry if these questions are stupid. I don't yet see what indication the controller has of temperature other than that, yet the Haynes write-up says that cycle times will vary with temperature?

    By the way, what is the exact name of the Haynes manual? I'll order one up from Amazon.
     
  6. 86dieselburb

    86dieselburb 1/2 ton status

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    Well to be honest i'm in the same boat as you, still learning about diesels. The inhibit switch sense coolant temperature and once the temp gets to 125 degrees it opens and that keeps the glow plugs from coming on. It should be located at the rear of the block on the passenger side of the motor. Couldn't tell you what it looks like though... havent gotten that far into mine.

    Yes depending on the tepmperature sensed by the inhibit switch the controller
    determines the glow plug cycle time. I believe the inhibit switch does this by voltage. The colder the temp the higher the voltage is sent to the controller then the controller cycles longer with more voltage or shorter for less voltage.

    The Haynes is called "Diesel Repair Manual". The book number is #10330. It covers GM and Ford diesels.
     
  7. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Well, I compared the diagram to what was under the hood, and now I finally know what's going on. One of the previous owners installed the new GP controller (in place of the factory M1008 CUCV controller, which is totally different) and simply left the inhibitor out altogether. The feedback wire just loops straight back without the inhibitor in series at all.

    So, my question to the group would be, does it REALLY matter that much? I guess what it means is that the glow plugs will do their thing all the time, even in the middle of summer or when the engine is still super hot from driving. I don't know if this is a killer or if it'll just shorten the life of the GP's a little. Since this truck is a weekend beater, I wouldn't be so worried about a slightly shorter life for the plugs.

    Or I could just convert to manual...
     

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