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No start condition - cover the exhaust with a rag and it starts

Discussion in 'Trucks [ Eighteen Wheelers ]' started by freightlinerman, Sep 5, 2012.

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  1. Sep 5, 2012 #1
    freightlinerman

    freightlinerman Road Train Member

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    Very interesting today, we had a Humvee with a 6.2 diesel V8 that would crank but wouldn't start. Someone stuffed a rag with their hand in the exhaust, sure enough it fired right up. What causes this? I didn't get to ask. I've never seen or heard of it. The engine had a strange lope to it too and idle, where the RPM's would rise up 100-200 or drop 100-200 and would stall out if you revved it up and took your foot of the throttle. This was also a freshly over hauled engine, basically the entire vehicle was refurbed.
     
    freightlinerman, Sep 5, 2012
    freightlinerman, Sep 5, 2012
    #1
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  3. Sep 5, 2012 #2
    IceCreator

    IceCreator Medium Load Member

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    Werent 6.2s naturally aspirated? So they would need backpressure. What does the exhaust look like? Is is straight piped?
     
    IceCreator, Sep 5, 2012
    IceCreator, Sep 5, 2012
    #2
  4. Sep 5, 2012 #3
    freightlinerman

    freightlinerman Road Train Member

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    No, it's not straight piped its a military vehicle in service as such, it is muffled. Yes, naturally aspirated. It shouldn't need a rag in the exhaust to start, so what did stuffing one in there accomplish.
     
    freightlinerman, Sep 5, 2012
    freightlinerman, Sep 5, 2012
    #3
  5. Sep 5, 2012 #4
    Heavyd

    Heavyd Road Train Member

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    Sounds like the engine is out of time. The rag thing baffles me, I would love to see that! Any way of making a video?
     
    Heavyd, Sep 5, 2012
    Heavyd, Sep 5, 2012
    #4
  7. Sep 5, 2012 #5
    freightlinerman

    freightlinerman Road Train Member

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    Possibly tomorrow. I will see.
     
    freightlinerman, Sep 5, 2012
    freightlinerman, Sep 5, 2012
    #5
  8. Sep 5, 2012 #6
    IceCreator

    IceCreator Medium Load Member

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    Backpressure?
     
    IceCreator, Sep 5, 2012
    IceCreator, Sep 5, 2012
    #6
  9. Sep 5, 2012 #7
    bender

    bender Road Train Member

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    The fuel system was too full of air to pop off all the injectors for it to start and run. So by stuffing the rag in the exhaust enough unburnt fuel was accumulated in the cylinders for it to start. It didn't run or idle well due to the air in the fuel system and the governor in the injection pump cannot operate correctly with air in the injection pump.

    You could look at it this way: Starting fluid or WD-40 can be used to prime an engine through the intake, so blocking the exhaust primes the engine too, just with the engines own limited fuel source.
     
    bender, Sep 5, 2012
    bender, Sep 5, 2012
    #7
    haycarter Thanks this.
  10. Sep 6, 2012 #8
    Pablo-UA

    Pablo-UA Road Train Member

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    new WD 40 does not fire in engine. old did.

    So use small LPG bottles (for lighter filling)
     
    Pablo-UA, Sep 6, 2012
    Pablo-UA, Sep 6, 2012
    #8
    bender Thanks this.
  11. Mar 25, 2015 #9
    COLE15

    COLE15 Bobtail Member

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    Mar 25, 2015
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    My unit has one of these HMMWV's in our motor pool that does this. I ussually cover the exhaust with a document protector. So it would not be a compression issue?
     
    COLE15, Mar 25, 2015
    COLE15, Mar 25, 2015
    #9
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