8V92 shutdown question

[Michael_e]

Been a little while since last posting...Doing everything possible to get our house sold, painting + painting + painting, so we can get moved to our new home.
Anyway, while painting i've been wondering about a few things; I've been led to understand that the 8V92s don't have that shutdown flap in the blower intake like the 8V71s. So, when i turn off the switch, what really happens to stop the engine? I'm trying to attach a pic so my questions make sense. The pic is of the top on the governor box (?) and has 2 air operated valves. The one on the right moves a lever that goes down into the governor box and on top is connected to the acelerator pedal; the air operated valve (skinner??) on the left controls a lever that goes down into the governor box. Is this the fuel shutoff valve? and on the far left is a screw-in electric control valve for the jake brakes.
I really don't want to try and start the engine until i know what shuts it off. Does that air operated valve on the left control the fuel rack position? Does it 'come on' when the engine is shutoff, closing off fuel to the injectors? I can go take any pictures you guys need to help answer any questions.
Details - 1955 GM Scenicrusier, repowered with 8V92TA, Allison 754, air throttle, currently replacing ALL wiring.

[RickB]

It is hard to tell from that picture but my guess would be that the one that goes to your accelerator pedal is your hi idle and the other one is your fuel shutoff.

Just a word to the wise, air up your bus before you try shutting it down as the fuel shutoff needs air to operate. In other words, you will not be able to shutdown your 8v92 until you reach around 90 PSI using the compressor on your Detroit to build up air.

So, if you have an access fitting and a compressor use it to get your pressure up before you start it if you are concerned about how to shut it off.

Don't ask me how I learned that one!!!

Rick

[wildbob24]

Those two devices are air cylinders. The one on the left is the shutdown cylinder. Pushing on that lever moves the injector control tubes, and thus the injector racks, into the no fuel position. In a pinch' you can reach in with a tool a manually push the lever to stop the engine. If you use your hand be careful not to place a finger between the cylinder plunger and the lever; it can and will bite you.

The cylinder on the right disables the throttle when you turn on the fast idle. The electric switch to the far left, in addition to being the jake switch is also the fast idle cylinder and buffer.

Both of these are controlled by Skinner valves mounted on the bulkhead. They are solenoid activated valves that control the flow of air to the cylinders

[Michael_e]

OK, let's see if i got this right, when the skinner valve that controls the shutdown cylinder is energized with electricity it RELEASES air pressure on the lever that moves the injector racks and ALLOWS fuel to flow. And when electricity is turned off it ALLOWS air pressure TO the air cylinder to move the injector racks to a closed position and shuts OFF fuel to the injectors. And somewhere in all this is the fast idle cylinder. There must be some interconnect between fast idle and air pressure in the system so that when the air pressure is up to operating pressure it then removes the fast idle feature allowing a normal engine idle speed.
The fast idle feature will be the next item i will want to talk about. BUT, let me know if i have the above info correct.
Right now i'm filling the air system via an external portable sears air compressor. It's hard to hear over the portable air compressor, but i think i've got some air leaks.
Thanks,
Mike

[JackConrad]

   Should be 2 skinner valves next to each other on the bulkhead. One is for the engine shutdown, operates as you said, Power to the solenoid keeps air fron going to the shut down piston top of the governor. Remove power (shut off engine) and air flows to engine stop piston. Yopu cannot sut off engine with switch until you have air pressure.
   The other skinner valve allows air to flow to the Fast Idle when power is applied. You will not have fast idle uintil you have air pressure.  Remove power (turn off Fast idle) and valve closes stopping air flow to the Fast Idle pistons (as well as venting the air already in the Fast Idle circuit to the atmosphere).  Jack

[RickB]

Michael,

The three truths of the universe:

There's no crying in baseball.

There's no Santa Clause.

Nobody trusts a 2 stroke bus owner without oil and air leaks.

So, with that said, welcome...

By the way, you had the high idle concept backwards. You need air pressure to engage the hi idle not the other way around.

You're in good hands with Jack. He's forgot more than I know about buses.

Rick

[Michael_e]

Well, getting one out of two right is like batting 500 in Baseball, right? Anyhooo... can't quite figure just where all that air is getting out. Checking my air gauge and the clock on the fridge, air pressure drops from 95lbs to about 20lbs in about 90 minutes. Must be some really slippery, well oiled air to get out without making a sound. Guess i'm going to wet wet and soapy soon.
Thanks,
Mike

[PCC]

Having an 8V92, I have been told that the engine shuts down by the ECM losing voltage, and not telling the injectors to open to inject fuel. So the engine fuel is shut off by the ECM and no fuel.

That is my understanding of it all. I learned this from DD as I tried to figure out why mine would not start, so I was looking for a fuel shut off system, and emergency shut down. I was told it is controlled by the ECM.

PCC

[Busted Knuckle]

Having an 8V92, I have been told that the engine shuts down by the ECM losing voltage, and not telling the injectors to open to inject fuel. So the engine fuel is shut off by the ECM and no fuel.

That is my understanding of it all. I learned this from DD as I tried to figure out why mine would not start, so I was looking for a fuel shut off system, and emergency shut down. I was told it is controlled by the ECM.

PCC

PCC,
If it is a DDEC (Detroit Diesel Electronic Control) engine it will be shut off by the ECM.
But in Michael's case he has a MIU (Manual Injection Unit) and his picture clearly shows the shut down cylinder next to the yellow wire!
If yours is DDEC it won't have this cylinder or even look like this as there will be a box with wires sitting where his governor is.
FWIW
  BK 

[luvrbus]

If your 8v92 has not been started for a long period of time the best and safest way is to remove a valve cover and clamp vise grips on the fuel rod that controls the injectors till you can be sure everything works properly    



good luck

[Iceni John]

Sorry to ask another dumb question:

Jack says (and I have no reason to doubt him) that you will not have fast idle until you have air pressure.   I thought one reason to have fast idle was to help build air pressure in the first place.   My fast idle switch doesn't do anything when I start the engine, so I have to hold my foot on the pedal to keep about 900 RPM.   My engine is DDEC II  -  does this change the operation of the fast idle compared with MUI?   So, does my fast idle have an electrical fault (because it's DDEC) or a pneumatic or mechanical fault?   Just curious, because in the big scheme of things this is not a biggy, just a nuisance.

John, idling away his time on this forum

[Busted Knuckle]

Sorry to ask another dumb question:

Jack says (and I have no reason to doubt him) that you will not have fast idle until you have air pressure.   I thought one reason to have fast idle was to help build air pressure in the first place.   My fast idle switch doesn't do anything when I start the engine, so I have to hold my foot on the pedal to keep about 900 RPM.   My engine is DDEC II  -  does this change the operation of the fast idle compared with MUI?   So, does my fast idle have an electrical fault (because it's DDEC) or a pneumatic or mechanical fault?   Just curious, because in the big scheme of things this is not a biggy, just a nuisance.

John, idling away his time on this forum

John if yours is a DDEC unit it is an electrical problem.
Also the purpose of "Fast Idle" is not to air up quicker but to allow it to charge better and less head pressure on the A/C compressor when on! FWIW
  BK 

[BUR]

As one gets older those air leaks seem to get quieter. Don't figure            BUR