Truck Started Cranking By Itself, key in the off position.

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by 5UG, May 27, 2024.

  1. 5UG

    5UG Light Load Member

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    Hello- (again)!

    I've got another question about a Paccar, although I don't think the engine type matters here.
    I was at the yard working on another truck, when out of the blue, the Paccar starts to crank! The truck never turned on, just kept cranking. The key WAS in the ignition, in the OFF position. The truck continued to crank, even after I pulled the key out!!
    I disconnected the battery to disable the truck.
    It was a cool, breezy, rainy day. Not sure whether that matters.

    Where do I start? (No pun intended.)

    Any ideas?
     
    Last edited: May 27, 2024
    Reason for edit: Corrected info: truck didn't turn on, only cranked
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  3. AModelCat

    AModelCat Road Train Member

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    Does this truck have the ability to start to charge low batteries or warm the engine? I'd start there if it does. If not, I'd start at the starter solenoid and work my way back to see what's feeding it power.
     
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  4. 5UG

    5UG Light Load Member

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    Thank you! It is not equipped to top off low batteries or warm the engine on it's own.
    I'll check at the starter solenoid per your suggestion. . . That's where my mind went too. Thanks again, I'm just scratchin' my head about what initiated the random, impromptu cranking.

    In any case,
    Kind regards
     
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  5. Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    I had the truck starter crank over while I was driving. It ended up to be the cables wearing thru the insulation which eventually passed current to crank the starter over. This was on my 1979 KW. My guess to your issue could of been similar however, the rain(moisture) gave it that extra boost.
     
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  6. 5UG

    5UG Light Load Member

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    May 22, 2024
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    Thanks for the reply!
    I can only imagine the expression on your face when that happened! Probably looked something like mine this evening. It was already getting dark outside when I was tinking around with the lights on the other truck. I'll have to crawl under and take a good look at everything during daylight. . . I'll be sure to check for what you've described with the insulation. That sounds very plausible indeed- especially with the rain!

    Love the look of those older KWs!

    Thanks again for taking the time,

    Cheers!
     
  7. AModelCat

    AModelCat Road Train Member

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    Had a machine light up inside the washbay one time because of rubbed through insulation on the positive cable. Was fine until the water hit it, then I'm yelling at the nearest apprentice to grab a wrench and unhook the batteries while I kept the water spray on the fire to keep it from going up lol.
     
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  8. Lyle H

    Lyle H Road Train Member

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    If that happened wouldn’t the starter have been spinning about 100,000 rpm’s?
    I can’t believe it didn’t explode or did it?
     
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  9. BoxCarKidd

    BoxCarKidd Road Train Member

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    Do starter drives not have a one way slip clutch so they do not stay at speed when the engine fires?
     
  10. Logginjim74

    Logginjim74 Bobtail Member

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    Could be an electrical glitch or a faulty ignition switch maybe? Since it's a Paccar, it might be worth checking the wiring harness too, just to rule out any potential shorts or loose connections.
     
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  11. Grumppy

    Grumppy Trucker Forum STAFF Staff Member

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    There's definitely a short somewhere. Check around the fuse panel(s) for evidence of shorting. Black marks, burned area's etc.

    My wife's Chevy Trail Blazer did the same thing. She was at work & someone came running in her office and told her, her car was cranking. The fuse block under the hood just started to catch fire when they got the hood up. It was burning by the time someone got a wrench to disconnect the battery. Obviously the fuse panel cracked or something and cause a short & caused the starter to start spinning.
     
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