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Old 10-23-2015, 08:36 PM   #1
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Year: 1997
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Fuel shut off solenoid woes.

Hello to all...
I have a 1997 Thomas Pusher with 8.3 Cummins and Allison 6 speed.
I drove this thing home in MAy 380 Miles without a Single Issue.
It has Been sitting in my Drive way since then.
I went to use it for a Road trip the First time 7 days ago, and The Fuel shut off Solenoid started acting up on me....Killed fuel after about 1/2 hr run time...I limped it off the Hwy.
Put new Fuel Filters on it thinking that was the issue first, Turned it around Head home, And it shut off on me again...
We pulled the unit Off, and Get it home. I bought a New Unit, same issue, and it is Random...? one time 25 mins, then only 10, then 2 hrs...?

I tested many things, thinking I had a Dead short somewhere...I think I have ruled that out now.

I think I have Determined that the Fuel shut off RELAY in the BAck of the Bus is Getting its Feed Power thru Wire number 193...? A red or red with black trace. But....? What I do not know , is where this wire comes from or goes to on the Bus or Motor...?

It either goes into a MODULE hiding somewhere, or direct to a Sender unit on the Motor..?

If Anyone has a Schematic of the Engine to Fuse/ breaker Panel wiring....I would Greatly appreciate a copy....
I read another thread where you guys Have Bypassed this unit, but I have much travelling to do, so i would Like to get to the root source of this Random Kill....

Many thanks in advance.
My Email is johnsc2c@gmail.com
John.
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Old 10-23-2015, 09:07 PM   #2
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Did you Check your ignition switch? We had a bus with these symptoms and it was the switch momentarily cutting off. I also think there might be a relay that powers the solenoid which may have gone bad. Those solenoids aint cheap if I remember...! Dooes your bus have all 6 gears unlocked?
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Old 10-23-2015, 09:14 PM   #3
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Charles.... I have done everything under the Sun.....lol...
I do not see the ingition dropping out.....I tried even wiggling and Banging on it to try and get it to fail....As it was first on my list of Culprits. I thought the relay may be the issue, but It does not lose Power that i can See when the Fail happens. But that Relay does get its CONTROL power / switching power from Wire ( 72 Blue/w trace ) at relay and it is wire 193 ( on Terminal Block ) in the Generic schematic I have...and That 193 Wire goes into the Engine Harness to somerthing....??? That is where I lose it...? So I need to know where wire 193 goes to on the Engine.....

My Money is Betting on a Oil sender unit.....And that is on its way out....but I absolutely HATE parts changing till I KNOW With DEFINATIVE Answers.

P.S. I dig your Busses......Watched Some Youtube stuff on you....;)
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Old 10-23-2015, 09:35 PM   #4
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Haha! Thanks for taking a look at it

Wire 193.... well good luck ;)

I don't have schematics, and that's what you need now! A dead short in the middle of a big loom is unlikely, at least, so once you figure out where that wire goes you're in for an easy fix. If there is such a thing
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Old 10-23-2015, 10:52 PM   #5
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How many wires does your Fuel shut off Solenoid have coming off of it?

Most I have seen on the mechanical engines are two wire. One positive, one negative.

The Fuel shut off Solenoid is activated by a source power current. Just wire it to a switch at your dash, being fed by a fused 12 volt supply.

When the stock wiring fails us at the shop, we tend to rewire things.

Nat
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Old 10-23-2015, 11:53 PM   #6
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I removed the fuel shutoff solenoid and replaced it with a mechanical rod. No more electrical issues to worry about but I do need to remember to cut it in & out.
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Old 10-24-2015, 07:20 AM   #7
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My issue was the solinoid that feeds the shutoff, it gives shutoff power to hold rod "up" or "on"

when power is turned off to the 1st solinoid it releases the shutoff solinoid and engine dies

My intermittent problem was the wire from solinooid to the shutoff was corroded and had broken wires, it became more of a problem as wires broke, it finally broke/corroded and wouldn't work at all

Hope that made sence
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Old 10-24-2015, 03:12 PM   #8
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I think you will find that most fuel solenoids will have two coils, thus two wires coming out of the body of it. One coil opens the fuel apparatus and then when the engine starts the second coil holds it open without the first coil.
The ground is completed thru the threaded hub so make sure that you take a rag and wipe those threads clean when installing the new one.
With an ohm-meter those two wires should not show continuity as they are separate coils but will show individual continuity to the fuel solenoid body itself. That is the correct way to test it.
You might just have to reversee your connections for proper operation in that case.
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Old 10-24-2015, 04:49 PM   #9
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Quote:
Originally Posted by nat_ster View Post
When the stock wiring fails us at the shop, we tend to rewire things.

Nat

I'm with Nat. Never worth trying to chase wires on these things. After all, its only 40' worth....one way.
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Old 10-24-2015, 04:51 PM   #10
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The OP can't use a push pull cable due to the bus being a rear engine.

I would just wire both the hot wires to a switch each.

On or off, no guessing, no chance of something failing.

As long as you don't mind walking to the rear of the bus, just mount the switches there.

Best part is it will be impossible to steal you bus because no one will know where the fuel kill switches are.

Nat
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