Fuel shut off solenoid woes.

64crew4x4 · 10-23-2015, 07:36 PM

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.

charles_m · 10-23-2015, 08:07 PM

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?

64crew4x4 · 10-23-2015, 08:14 PM

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....;)

charles_m · 10-23-2015, 08:35 PM

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

nat_ster · 10-23-2015, 09:52 PM

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

Tango · 10-23-2015, 10:53 PM

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.

bansil · 10-24-2015, 06:20 AM

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

BlackJohn · 10-24-2015, 02:12 PM

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.

opus · 10-24-2015, 03:49 PM

Quote:

Originally Posted by nat_ster

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.

nat_ster · 10-24-2015, 03:51 PM

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

64crew4x4 · 10-24-2015, 04:16 PM

Here is my one issue with all this.... I know the Control Hot wire to the Relay is Run thru a Sender unit off the Motor, It is wire number 193 in the Engine harness. This Wire goes to TB ( terminal bus ) and ties to the wire number 72 on the control side of the relay for the HOLD wire on the Fuel Shut off Solenoid.

My Issue is if I bypass...( easy to do ) what sender unit am I bypassing, and What happens when it totally fails....As right now it is Only randomly dropping off for a moment... Am I losing Oil pressure, or Water Temp action...? I will be driving this Bus Coast to coast once a Month min.....And I do not want to start by passing and Jerry rigging it right out of the gate....I would Much Prefer to do it right the first time....

I guess I am Stuck till Monday When I can call Thomas up and get a Wiring diagram for this Age of Bus....??

BlackJohn · 10-25-2015, 10:50 AM

Just did a google search and they have everything you are likely to need to know for the 8.3's

64crew4x4 · 10-25-2015, 11:29 AM

Who has everything I need to know..?

Link..? ya lost me.....??

BlackJohn · 10-25-2015, 01:04 PM

just type in fuel shutoff solenoid in a search engine and you will find pages about your problem and drawings also.

64crew4x4 · 11-05-2015, 09:54 AM

Update.

BlackJohn.....I did a searh as you suggested...I came up with nothing I didn't already have....

I did Get Some better Info out of Thomas. Their Tech support guys are A-Ok in my book.

So I have 3 Constant Duty Solenoids on my Bus...One in the Rear 150 Amp, 2 up front.
After replacing all 3 Batteries, and Cleaning everything I could Find to Clean, I decided to Pull and Clean all contacts on the Duty Solenoids, as they provide positive power to most everything on the Bus inside and out. When I went to break the Nuts loose One completely crumbled in my hands....the other was complete, but the Black Plastic was cracked 2 directions. So I think..Ah haaaa.....I finally found my issue.... I replaced all 3 of them. Fired the Bus up, it ran for 3 hrs With no Failures....then boom...random, just drops and Dies again. FUTHER MUCKER PUCKER TRUCKER......

So I get back on the phone with Thomas Tech support, and We go over everything again....

The only thing I have not done to this Point is Pull the Entire front panel apart, and Clean every single Fuse and Contact location....

I have Found that My Root Problem is that i am Loosing Voltage /amperage when I start to run Any Load....ie: Lights, Heater fans, interior lights.

It is Very Random though... One time All things on Full Load no fall off die...the next time, just lights on, it dies.
next time lights, and one fan...it dies.

Then All loaded no issue, rev motor to say 1800 rpm..back to idle...it dies.

Here is a list of things I have done to this point to try and Kill the Drain...

New Batteries X 3
Tested Alternator...it tests Loaded good....at 150 Amps
New Shut off Solenoid.
New Fuel solenoid Relay
New Constant duty Solenoids X 3
Cleaned all wires at the Starter,
Cleaned all Hot wires and grounds at the Rear Panel box
Cleaned the Duty Solenoid bases , and Power bars in the Front panel by drivers window.

I have not replaced the Fuse breaker( thermo breaker ) units associated with the Fuel shut off circuit...I am going to do that today with Regular fuses. Thomas Bus Tech support suggested I do that , so I am about to go try and Test that theory out....

If any of you guys have any other suggestions, I am All ears.....

I know I can Bypass everything and It will run, issue is , the Voltage / amp drain is still there... So If I am Trvelling across a Remote Pass somewhere at midnight, and the Bus Losses Power completely, I am FUBAR... I need to get to the Bottom of this Drain issue, before I can Commit to Open Road Travel.....

Thanks in advance,
A frustrated John in Oregon.

RHOMBUS · 11-05-2015, 10:40 AM

I'm sure you've checked all of the little things but here are 2 I didn't see mentioned:

My buddy's bus would't start due to the rear engine door not being fully closed. There's a switch in there that completes the circuit.

My bus wouldn't start because the rear window switch wouldn't register as closed.

My biggest electrical fault was that the ground wire from the battery to ... everywhere it went, was corroded, inhibiting full power from the alternator.

Both buses are Thomas rear engine, 2001, 2002, one Cummins, one Caterpillar.

64crew4x4 · 11-05-2015, 12:12 PM

RHOMBUS.....

Thanks....I have verified all those Are in Order...Some have been Deleted Prior to Me...also, This Bus being a 1997 Does not have Rear Engine Door Buzzer....I can Run it with Door open and up with no issues....

It fires Every time With no issue...like Turn Key on, count to 5 letting the Dash lights and Systems Check, then One or 2 Revolutions and Fire....

Firing up has Not been an Issue ever....its the Fuel shut off Letting go of the HOLD....and Killing the motor once loaded.

But again, thanks for the Thought....

BlackJohn · 11-05-2015, 03:00 PM

Thanks for the update John. Puzzling for sure but...here is what I did when I got my bus with the old cat 3116 FE. I decided it wasn't worth converting if the electrical systems weren't in top notch shape. The engine ran great and still does. Having worked around these types of relays, solenoids and such all my life I decided to remove any and all panels on the front dash and gain access to most everything. What a shock! There was dust bunnies and so much debris in there it's a wonder there was never a fire. This is all due to the air currents flowing in back of the panels and accumulating on everything electrical. So with a paint brush and vacuum cleaner I did what was necessary. Cleaned it all up good so I could see everything going on. Lots of black too from diesel fumes migrate into these areas.
I decided to clean all connections one at a time as best as I could and get new shine on all contact areas electrically. What I couldn't see right away was corrosion on the blocks that the fuses and relays plug into so apart they came too. if I hadn't done all this finicky cleaning I would be having major problems today. As it is everything is as good as new behind the dash panels.
Even the heavy fuses and relay blades had a certain film build up over the years that impedes good continuity in a circuit. Time consuming yes but then you aren't guessing anymore as to what is a good connection.
Ok so the fuel solenoid has the two coils in it as we discussed. One works initially in the start up parameters according to what your bus calls for. It works at a higher current until such time as oil pressure and engine temps are reached or a failure in those systems is found to be which then shuts the fuel off, saving your engine and your ass. This is why this is crucial to have working properly. So, when oil press is fine and operating temp is reached, the second coil in the fuel solenoid is energized at a much lower current than the startup coil of the fuel solenoid. The bus should operate until you shut down yourself then.
I suggest you undo the two wire connections at the fuel solenoid and interchange them and give that a try.
To try and rig your bus so it runs isn't the way to go as you are travelling cross country. This can be made to run properly.

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