88 B600 6.6 diesel---where are the relays for the fuel cutoff solenoid?

[Moparman5.9]

I am troubleshooting my fuel cutoff solenoid system, solenoid doesn't stay pulled in with key in "run", there is supposed to be a relay for this---does anybody know where Ford hid it? If any body has any info on this it would be appreciated, especially pics, wiring diagrams, etc. Thanks in advance.

[Robin97396]

A mopar man with a Ford! To start with, isn't there something wrong with that?

I don't know where your relays are, but it's not uncommon for a shutoff valve to go bad now and then and cause all kinds of havoc.

[Jolly Roger bus 223]

Don't know it will help but I have all the ford with Thomas body wiring diagrams for an 86 B700 with an 8.2.
I don't see a fuel solenoid switch?
Maybe troubleshoot your pump,fuel pressurized and return lines and filters?
Might be wrong but it's usually back to the basics on almost anything in the 80's the electronic mess didn't really start until 92 at the earliest but most were mid to late 90's.
And I might be off some years but in the 80's they still had a mechanical fuel pump.
Good luck

[Robin97396]

I'd also expect that to be a manual fuel shut off valve, unless someone is tracing out wiring from the valve. The manual valve could have been replaced.

[Jolly Roger bus 223]

Yeah, your correct.
But even if the bus barn had the parts laying around and new exactly how to wire it?
That would have been an expensive and time consuming upgrade to an 88 model

[BlackJohn]

Originally Posted by Moparman5.9

I am troubleshooting my fuel cutoff solenoid system, solenoid doesn't stay pulled in with key in "run", there is supposed to be a relay for this---does anybody know where Ford hid it? If any body has any info on this it would be appreciated, especially pics, wiring diagrams, etc. Thanks in advance.

So, 2 wires on the fuel solenoid on your rig?
One does the pulling open to start, the other does the holding open when in run position.
I assume the engine will start but quits when you let the key go?
Check for bad ground from the block to the chassis first then ring out the solenoid for continuity of each coil in it. If you have a bad coil replace the fuel solenoid. They do get hot and burn up.
As for the relay, all the relays are generally all in the same place, sometimes unmarked. Just pull one at a time and try to start. If you have the same condition upon pulling each relay, keep on trying till you get a no start condition. That will then be your fuel system relay if there is such a thing. That should in turn have its own fuse but I think it is ok from the start condition you have described.
Those solenoids are rather expensive on any bus. You can't do without it unless bus can remain parked.

John

[Robin97396]

I assumed it had been some time since this '88 had seen a bus barn. Lots of time for backyard mechanics to make changes. Besides, you know what happens when I make an assumption

[Moparman5.9]

Originally Posted by Robin97396

A mopar man with a Ford! To start with, isn't there something wrong with that?

I don't know where your relays are, but it's not uncommon for a shutoff valve to go bad now and then and cause all kinds of havoc.

Yes, there is something wrong with a mopar man with a Ford! I just couldn't find an affordable mopar bus with a mechanically injected diesel !

The way I understand it works is that the solenoid is actuated with a full 12volts in "start", then as the key is released to "run", the relay sends a lower voltage to the solenoid through a resister to keep the solenoid pulled in, but to avoid overheating the solenoid coil.

The bus will run with the solenoid pulled and zip-tied open, and shuts off when I cut the zip tie. I know there is voltage to the coil in "start" becuase the solenoid actuates in Start , but releases in run, shutting the fuel off. logicall, this would mean the solenoid coil is OK, just a fault in the voltage dropping circuit.

[BlackJohn]

Originally Posted by Moparman5.9

Yes, there is something wrong with a mopar man with a Ford! I just couldn't find an affordable mopar bus with a mechanically injected diesel !

The way I understand it works is that the solenoid is actuated with a full 12volts in "start", then as the key is released to "run", the relay sends a lower voltage to the solenoid through a resister to keep the solenoid pulled in, but to avoid overheating the solenoid coil.

The bus will run with the solenoid pulled and zip-tied open, and shuts off when I cut the zip tie. I know there is voltage to the coil in "start" becuase the solenoid actuates in Start , but releases in run, shutting the fuel off. logicall, this would mean the solenoid coil is OK, just a fault in the voltage dropping circuit.

There are 2 solenoids inside the one main body. The start one is fine. The run solenoid is defective. The operating voltages may vary but one coil is surely defective.

John

[Robin97396]

That sounds about right. Electronic shutoffs simply go bad, and frequently at the worst possible time. Most of us, or at least some of us, would like a manual fuel shutoff.

I could change mine but it's not broke yet, and if it ain't broke don't fix it.

[Tango]

Cummins have also had "issues" with the fuel solenoid but it is an easy fix. Remove the solenoid, throw it away, and attach a steel rod to the fuel lever that the solenoid moves.

Easy, peasey. Push, pull. No electrics to go bad at the wrong time. That is exactly what I did on my 4BT.

[Moparman5.9]

Originally Posted by BlackJohn

There are 2 solenoids inside the one main body. The start one is fine. The run solenoid is defective. The operating voltages may vary but one coil is surely defective.

John

Thanks, that clears it up, if there are two coils in the one solenoid I can check both tomorrow, that seems like the most likely issue.

[Moparman5.9]

Originally Posted by Tango

Cummins have also had "issues" with the fuel solenoid but it is an easy fix. Remove the solenoid, throw it away, and attach a steel rod to the fuel lever that the solenoid moves.

Easy, peasey. Push, pull. No electrics to go bad at the wrong time. That is exactly what I did on my 4BT.

Yes, the 6.6 looks pretty easy to modify with a push-pull type cable, might do that in the future.

[Moparman5.9]

Troubleshot this morning, definitely has a bad run coil. Will be ordering a shutoff solenoid today. Thanks for everyone's help.

[EastCoastCB]

Originally Posted by Moparman5.9

Troubleshot this morning, definitely has a bad run coil. Will be ordering a shutoff solenoid today. Thanks for everyone's help.

Black John and Tango are SUPER helpful folks!

[nevrenufhp]

Not sure if you found em yet, but for some reason Ford put em behind the glove box.

[Moparman5.9]

Yes, I did finally find the relay. I ended following the wires back into the bus , wiring diagrams for these buses seem to be hard to find!!
My relay was bad and the connector had gotten very hot. Ford does not make the relay anymore (at least according to my local dealer). I ended up replacing the connector and using an ISO relay in place of the original. Here are some pics that may help others: