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Author Topic: MC9 shutdown solenoid problem  (Read 1275 times)
Bruce MC9
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« on: August 26, 2009, 11:19:38 AM »

I am having a problem with my '82 MC9. It starts fine but when the air pressure reaches 75 psi, the shut down cylinder activates and shuts the engine down. I have checked the valve that feeds this cylinder and it is not receiving 24 volts unless the engine is started from the rear. I am assuming that this is because of a shut down feature like the low oil shut down. What other conditions will cause the engine to shut down and how do I go about checking the sensors to make sure that they are functioning correctly? Detroit diesel 6V92, Allison HT740
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bevans6
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« Reply #1 on: August 26, 2009, 11:24:55 AM »

Not a total solution, but maybe a trouble shooting aid.  Your bus, like mine, has a pressure protection valve in the air system that doesn't pass air into the Auxiliary air tank until the service tank pressure is over 65 psi.  The shut down system is two-stage - a skinner valve that is electrically operated by the switches, and an air cylinder that gets air sent to it via the skinner valve, and the key is that the air comes from the auxiliary tank.  So when you are first pumping up your air system, the shut-off valve won't work until the air pressure is over 65 psi.  In your case, it always works as soon as the air pressure gets to 75 (close enough to 65 for gubbmint work), so it's possible that the skinner valve has failed and is always passing air to the shut down air cylinder.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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luvrbus
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« Reply #2 on: August 26, 2009, 11:25:52 AM »

Turn your dash switch on if they are not on it will shut down when the air pressure reaches about 70 lbs when starting from the rear  and make sure the rear start is off when using the front dash start

good luck
« Last Edit: August 26, 2009, 11:45:58 AM by luvrbus » Logged

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buswarrior
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« Reply #3 on: August 26, 2009, 07:38:50 PM »

What we're all trying to say: The electric circuit to keep the air pressure from acting on the mechanical shut down that turns off the engine is failing.

Power is not reaching the solenoid to keep it open. Broken or corroded wiring, check both the supply and the ground. Might go all the way back to the switch.

let us know how you make out!

happy coaching!
buswarrior

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Frozen North, Greater Toronto Area
gumpy
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« Reply #4 on: August 26, 2009, 08:07:38 PM »

You might want to check the stop/run switch on the rear panel and make sure it's in the run position and not in the stop position. Having it in the stop position
will cause the problem you describe. Been there, done that.

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Craig Shepard
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NewbeeMC9
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« Reply #5 on: August 26, 2009, 08:41:21 PM »

What Gumpy said. Smiley

I had a turn also, Wink

Guess its your turn Bruce MC9 Cheesy    your "run" switch on the  rear start box is in the wrong position


Welcome to bussing and the board.
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It's all fun and games til someone gets hurt. Wink
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