M923 NHC250 Ether Pressure Switch

[Swamp Donkey]

From what I can tell, the switch below the pump in the picture is the pressure switch for the ether system. Is that correct?

If so, is that the only thing it signals? Can it be removed and plugged if I'm not worried about the ether system working correctly.

In the picture you can see it's leaking from the connectors. I not interested in replacing the switch for a system I'll never use, unless it will affect something else. I'd rather just remove the switch and terminate the wires if possible. I can't find a definitive answer on whether this is possible though.

 

[Floridianson]

Was that not part of the Diagnostic system, anyway just a port into the PT. I would dump and plug.

 

[Swamp Donkey]

I thought the unit on top, with the 3 or 4 wires, was for the diagnostics? I verified the bottom pressure switch wires were #570 per the schematic below, so bottom switch is for the ether. Just wanted to verify it was only for the ether system. I'll remove the switch and plug it. I'll probably remove the rest of the ether system too. I want to eliminate points of failure for things I don't use, with this switch being a good example since it's leaking. I have a block heater and, if absolutely necessary, can spray my own ether.

Is the unit on top only for diagnostics or is it necessary for the truck to run properly? I found where someone had to replace one but haven't found where anybody removed it from the pump permanently.

 

[M35A2-AZ]

Yes the one on the bottom can be removed, I have a truck that does not have it installed.

 

[74M35A2]

Is the pump OK with this not present? Is there a lever inside that pushes on the switch, or is it simply a fluid pressure? If a mechanical push, I'd ask around about it more. If a fluid pressure switch, I would just plug it. Well, actually, I live in MI and would replace the switch. We get as cold as -10F and colder, and the ether saves the starter and batteries. Some use it, some are super strictly against it. Regardless, I think you should remove the switch and see if it is drilled with a fluid port. If it has a mechanical ball on the end or a push pin, try to find out if operation without it is OK (Cummins service center maybe).

 

[M35A2-AZ]

Yes it works just fine. I think it is just a pressure switch.

 

[Swamp Donkey]

It's just a pressure operated switch that operates around 3-5 psi. From what I can tell it just let's the ether system know there is fuel pressure present before it'll activate. Just wanted to make sure that's all it did.

I'll remove it this evening. I'll have to disassemble the harness running below and to this switch though. The fuel ran down the wires and is now inside the wire loom. What a mess. Luckily it just started leaking yesterday.

Now that this port will be free, would there be anything gained by having a gauge here instead of just plugging it? Is that a useful place to have a gauge at that part of the pump?

 

[Floridianson]

OK bottom one is used to make sure the cold start can not be used when the truck is running and top is the Diagnostic.
I did not have a 939 series that long and tried to get through the TM's. I don't like gages install in the engine compartment and left there. Guess if you had one you could hook it up and see if it reads true rail pressure.

 

[Swamp Donkey]

Good point about the gauge being left unattended. I'll just plug it and be done with it. Don't want to end up in the same boat if the gauge decided to leak.

 

[Gunzy]

Depending on the pressure you could run a line to the dash and install a fuel pressure guage there if it is rail pressure.

 

[Swamp Donkey]

I just went ahead and plugged the ether switch port and terminated the wires going to it. Problem solved. Now on to part two...

I unplugged the diagnostic sender and the truck started fine. I plugged it back in and restarted the truck. I unplugged it while the truck was running and nothing happened. So is this purely diagnostic or does something on the truck use it that would affect operation? I can't think of anything of hand that would need it, but I might be missing something.

This picture of the wires is why I'd like to do away with it, along with the potential for another leak. That harness was tangled in the throttle linkage when I got the truck. I can't see going to the trouble of repairing the wiring for something I won't use.

 

[Floridianson]

yep I would dump and plug too! If you do check rail pressure when I checked Pete's it was defueling at 190 psi.

 

[wcuhillbilly]

Both of my PT pumps have it plugged,,, Or let me rephrase this,,,, the NTC 350 is plugged, the NHC 250 "had" the hand primer plumbed in there. 1/8" pipe plug....
Dump and plug..... just plunky gear,

 

[Swamp Donkey]

yep I would dump and plug too! If you do check rail pressure when I checked Pete's it was defueling at 190 psi.

The pressure I would see was going to be my next question. I didn't want to get an underrated gauge. I'll have one on hand if I ever need to check it in the future though.

Both of my PT pumps have it plugged,,, Or let me rephrase this,,,, the NTC 350 is plugged, the NHC 250 "had" the hand primer plumbed in there. 1/8" pipe plug....
Dump and plug..... just plunky gear,

That's good to hear. Those mangled wires have bothered me since I got the truck.

If anybody needs the part of the ether system mounted to the washer bottle bracket, you can have it for free if you pick up the shipping. I don't know what is there, if it's all there, what it does or if it works. I don't know anything about that system. I'll leave the offer up for a week. After that it'll be trashed. The dash switch stays with me.