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Runaway 6-71 Detroit

Discussion in 'Other Construction/Demolition Equipment' started by PonderosaPete, Jun 14, 2019.

  1. PonderosaPete

    PonderosaPete Member

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    I've got an '85 Ford L9000 with a Detroit 6-71 engine. Engine was running fine and I decided to pressure wash it this past Sunday. Truck sat until yesterday because I was doing some brake work on it. Went to start it yesterday and the engine was full throttle and ran away. I had to put it in gear and let the clutch out to shut it off. Any idea of what could be wrong or is it just a coincidence and an injector is stuck open. Like I said, it ran fine before I pressure washed it. Could it be possible that the pressure washer knocked a wire off? I don't believe the injectors are electrical; am I right? Guess I just should have left the engine filthy dirty. I took the air intake elbow off and covered it with a piece of sheet metal and tried it again with the air throttle down, and it smokes like hell with black smoke. Any and all advice appreciated.
     
  2. Vetech63

    Vetech63 Senior Member

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    Remove the valve cover and check for a stuck injector control rod. It could be any one of 6. The best way is to pull the engine kill cable and see which control rod doesn't move.
     
  3. PonderosaPete

    PonderosaPete Member

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    There's no engine kill cable. It turns on and off with the key.
     
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  4. Vetech63

    Vetech63 Senior Member

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    You can still do the same thing with the key.
     
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  5. PonderosaPete

    PonderosaPete Member

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    Guess I'll give it a try. I wish there was something easier than taking the valve cover off. I'll probably do it tomorrow, weather permitting - it's outside. Thanks. As far as you know, there's nothing electrical on those valves, right? Funny thing is, I knocked the wire off the shut-off solenoid while pressure-washing and I had to solder a new terminal on that to repair it.
     
  6. kshansen

    kshansen Senior Member

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    Yes! Do not even think about starting it until you remove the valve cover and confirmed all six injector rods move in and out nice and easy.

    Does this engine have the emergency shut down flapper in the inlet to the blower? If you don't know what I'm referring to let us know and one of use should be able post a picture.

    One more thought can you post a couple pictures of the engine, one from each side? Might see something else to ask about!
     
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  7. PonderosaPete

    PonderosaPete Member

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    No emergency shut down flapper. Wish it did! I had to take off the big rubber air intake elbow and use a piece of sheet metal over the air intake to shut it down. It's pretty scary when that thing is running and you can't shut it down. Good idea - I'll take a couple of pictures and post them tomorrow.
     
  8. thepumpguysc

    thepumpguysc Senior Member

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    Removing the v. cover will tell the tale.. Sorry for your troubles.. Good luck.
     
  9. Junkyard

    Junkyard Senior Member

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    First runaway I ever had was a 6-71. Sound like a tornado siren when they wind down. Consider it a test of the bottom end :)

    Like they said above the only sure way is to pop the valve cover off and take a look at the injectors. Nothin electrical related to the injectors or rack under there. It’ll be obvious if there’s one stuck.
     
  10. RZucker

    RZucker Senior Member

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    I doubt pressure washing did anything that requires removing the valve cover, I would like to see pics of the governor and the blower. Especially the shutdown solenoid and the throttle linkage.
    Did this engine overspeed? or just go to 2100 RPM and stay there? Lots of variables here. Is there an air controlled PTO throttle...? Heck, something may have been knocked over center in the linkage when it was washed. Seen it.
     
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  11. Vetech63

    Vetech63 Senior Member

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    If your injector rods are ok check your air box drains. I have seen 2 run away from oil build up because someone plugged those drain hoses thinking they were stopping oil leaks.
     
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  12. PonderosaPete

    PonderosaPete Member

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  13. PonderosaPete

    PonderosaPete Member

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    As you can see above, I was able to get the cover off and take a couple of pictures. Don't really know exactly what I'm looking at. I see one injector that's noticeably lower than the other 5. You can't really tell from the picture. I'm thinking that could be the one? If it is, how do I get it unstuck. I have the two fuel lines off of that one but there/s really nothing to pry against. I don't want to pry against the rail as I don't want to bend or break anything.
     
  14. Birken Vogt

    Birken Vogt Charter Member

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    You need to use the key or jumper the shutdown solenoid or whatever it takes to work the rack control rod from WOT to shutdown with the engine not running. All the injectors have a little rack that runs in and out of them. One may not be moving. The arms that stick out from the main rod/tube should all move in unison. Those breakaway springs are there to allow a stuck injector not to stick up the whole works.
     
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  15. GregsHD

    GregsHD Senior Member

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    Looks like an air shut down cylinder.

    Its pretty hard to get a full blown run away with that style rack if only one injector is stuck.

    Gently clamp a small pair of vice grips on the rack tube, it should rotate easily between full fuel and off.

    While operating the rack watch the individual control rods on each injector down close to the head, make sure they all move in unison.
     
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  16. RZucker

    RZucker Senior Member

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    With the key turned on or the air line to the stop cylinder disconnected.
     
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  17. GregsHD

    GregsHD Senior Member

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    I'm not familiar with that style governor, there's talk about an electric shut down solenoid, does it have air throttle instead? That cylinder certainly looks extended.

    Edit!! guess I should have read the first post!!
     
  18. PonderosaPete

    PonderosaPete Member

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    How much should they move? I tried it without the air shutoff disconnected and without the key and they don’t move very far. Got hungry and taking a dinner break so I’ll give it a try with the key on and the air shutoff disconnected tomorrow morning. Thanks for you help!
     
  19. RZucker

    RZucker Senior Member

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    Is there a gap between the low plunger and the rocker arm? if not it's just in the firing position for that cylinder. Do not pry against anything. Why did you pull the fuel lines?
     
  20. PonderosaPete

    PonderosaPete Member

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    Greg, it is extended. It’s in the shutdown position right now.