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Author Topic: Engine dies @ 60 lbs  (Read 2469 times)
gumpy
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Slightly modified 1982 MC9


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« Reply #15 on: November 13, 2006, 07:36:55 PM »

thanks fellows .i still cant figure it out . what could make it shut down at 60lbs consistantly? thanks jim

Go back and read my post above.

It's shutting down normally. If you watch your shutdown cylinder as the pressure comes up, you''ll see it activate and activate
the fuel cutoff lever. The solenoids are spring loaded, and they won't overcome the spring until the pressure reaches around 60 psi.

It's either the rear control switch is in the off position, or it's one or more of the safety shutdown system sensors related to low oil pressure, high temp, or low water level.

Do you have a manual?  Look at the safety shutdown electrical schematic.

By the way, if you air the bus up with shop air, it won't start at all, or, more likely, it'll start and die when you release the start button.

You didn't say what you've done to find the problem. It' working the way it's supposed to. Troubleshoot as indicated above.


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Craig Shepard
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http://bus.gumpydog.com - "Some Assembly Required"
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« Reply #16 on: November 13, 2006, 09:24:33 PM »

Jim, the auxiliary air system is probably the source of the air for the air shutdown solenoid. Since no air is passed from the primary air system unltil the minimum pressure valve is overcome (about 65 psi on ours), no shutdown occurs until that pressure is reached. When that pressure is reached, the pressure stops rising on the primary side while the auxiliary side catches up. Then, they rise together.

After the air in the auxiliary system bleeds off, the solenoid relaxes, opening the rack.

What can be humorous is that you can have just one air leak, the solenoid itself, and it will cause all of the symptoms that you are getting.

Good luck on finding your leaks and the cause of the shutdowns.

Tom Caffrey
Suncatcher
Ketchikan, Alaska
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Tom Caffrey PD4106-2576
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Ketchikan, Alaska
gumpy
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« Reply #17 on: November 14, 2006, 04:58:40 AM »

Jim, the auxiliary air system is probably the source of the air for the air shutdown solenoid. Since no air is passed from the primary air system unltil the minimum pressure valve is overcome (about 65 psi on ours), no shutdown occurs until that pressure is reached. When that pressure is reached, the pressure stops rising on the primary side while the auxiliary side catches up. Then, they rise together.

Yeah, that's a better explaination why it happens always at 60 psi. I like that better than my spring theory† Cheesy

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What can be humorous is that you can have just one air leak, the solenoid itself, and it will cause all of the symptoms that you are getting.

An air leak is not causing the problem. That's an electrical problem.

Most all air systems leak down, and what Tom said is true in that once the bus shuts down at 60 psi, it will not take long for the pressure to drop back below the magic 60 psi again, and the whole thing starts over next time you start the bus.

The problem is electrical.

« Last Edit: November 14, 2006, 06:40:11 AM by gumpy » Logged

Craig Shepard
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« Reply #18 on: November 14, 2006, 06:19:31 AM »

Craig is correct... the problem is electrical. Something, a bad sender or relay, is tripping the shutdown circuit. Unless you really do have low oil pressure (possible) or high water temp (impossible on a cold start).

If you can find the shutdown relay, you can readily bypass it to begin your troubleshooting.

HTH,
Brian B.
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Brian Brown
4108-216 w/ V730
Longmont, CO
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