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Author Topic: Engine shutdown activates when starting engine  (Read 928 times)
Larry B
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« on: January 31, 2013, 07:34:32 PM »

  I have an 8v71 that starts immediately (no cranking). I do not think there are any more than 3pistons that go over TDC and the engine fires up. If the bus is not aired up it stays running. If bus is aired up the engine guard shuts things down. The engine goes through this start up and shut down sequence usually twice sometimes three times before it stays running. I removed the wire going to the low pressure oil sender which actives the engine guard. The engine does not shut itself down with this wire removed. I removed the low pressure sender and tested it on a test guage and air regulator. The sender is set at 3 psi trip point as manual says it should be. I believe what is happening is the engine is starting before a minimum of 3 psi oil pressure is established and soon as the start button is released the engine guard takes over and shuts engine back down. Has anyone elsed experienced this ? Besides the starting and auto stopping being annoying, is the fact that my engine wants to start before 3psi oil pressure is establish something I should be concerned about? When the engine starts my guage reads about 35psi and drops to 20 after engine warms up (at idle-550rpm)
               Larry B
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1977 MCI-5B---
8V71- 4speed man
Brassman
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« Reply #1 on: January 31, 2013, 08:02:50 PM »

You know, I don't have an 8v71, but your post sounds like many others in the past. The replies always mention the Skinner valve. It's an engine shutdown. It needs air pressure to close the fuel.
« Last Edit: January 31, 2013, 08:05:53 PM by Brassman » Logged
lostagain
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« Reply #2 on: January 31, 2013, 08:28:17 PM »

Engine off switch is on at the back? Tripping the Skinner valve to activate the stop cylinder on the governor as soon as there is enough air pressure.

Also look at the ground connections for the emergency shut down. On my bus, on the driver's side engine cradle rail. I had a similar problem a couple of years ago.

Good luck,

JC 
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Rick 74 MC-8
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« Reply #3 on: February 01, 2013, 05:48:43 AM »

The way I understand it it's working as it should. There is also a fuel pressure sensor that overrides the starter button if that is working correctly you can hold the start button to override the engine guard until oil pressure is reached. On my MC-8 there's a relay in the rear junction box that went bad it had to crank until enough oil pressure was made. I don't trust the fuel pressure sensor I just start it 3 times. Not sure what's harder on the starter grinding it if the fuel pressure sensor fails or starting at 3 times. Lol




Rick 74MC-8
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« Reply #4 on: February 01, 2013, 05:53:42 AM »

Most of our older MCI's exhibited this issue.  And you have hit the nail on the head.  You can just hit the starter again or hold down the starter button until it continues to run.  Could also be the fuel pressure switch.
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Larry B
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« Reply #5 on: February 01, 2013, 06:27:32 PM »

I am glad to hear that this annoying situation is not only common to my engine. I did a couple of things today and for the present time this shutting down seems to have stopped. Like lostagain suggested I put a new ground wire to the oil block assem sitting on the drivers side engine rail. I removed all the pieces on same oil block assem. blew the little manifold out with air in case something was inside blocking oil flow. (silicon from gasket). I also installed new oil supply line from engine block to little oil manifold and this time I made hose longer and connected closer to low pressure sending unit in hopes that unit would sense pressure quicker.This manifold has a continuous flow through it on its way to rear of air compressor. I took skinner valve and air stop cylinder on top of govenor apart and cleaned yesterday. I started engine from rear and watched air stop cylinder on top of govenor. I restarted the engine three times after all this and it did not shut itself back down. After letting go of the start button you can STILL see the air cylinder extend 1/2 its full travel and then retract again. I am not real sure what corrected the issue I was having but it is gone for today at least. I would like to thank all who spoke up with their helpful hints.
            Larry B
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1977 MCI-5B---
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lostagain
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« Reply #6 on: February 01, 2013, 06:55:03 PM »

Good going Larry! Sounds like you did the right thing. If it works this way, great. If not, onward to the next idea.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
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« Reply #7 on: February 02, 2013, 07:37:40 PM »

Your bus is working as it's supposed to. You need to hold the start button down until the oil pressure light goes out.

Was going to call it operator error, but I think it's probably more like newbee lack of information.  Roll Eyes  By the way, we've all been there and learned that.
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Craig Shepard
Located in Minnesquito

http://bus.gumpydog.com - "Some Assembly Required"
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