Onan MDJE diesel fuel shutoff solenoid

[Bob Bradley]

My Onan quit (again) a couple weeks ago. Was running fine and simply shut down. I finally looked at her yesterday, and can only get her going by holding in the shutoff solenoid plunger while someone else starts the genny. Oil pressure is fine. Other than low oil pressure or hitting the STOP switch, what else activates the shutoff solenoid (cooling h2o sender, other)? I don't want to spend the $$ just to replace it and hope for the best. If it is getting a false signal I need to fix the real cause.

There are 2 wires to the top of the solenoid. Will I get a 12v+ reading at one of the solenoid wires only when the solenoid is being activiated? Or is there always 12v+ there, and it is interrupted by the stop switch to activate the solenoid?

Can anyone confirm my presumption that the solenoid is activated by having 12v+ sent to it when the "off" switch is hit? I'll be down there with an assistant tonight, and it would be helpful to know what to look for ahead of time. Thanks.
Bob

[mike parodi]

Had same problem. It was a bad oil pressure transucer, my oil pressure was ok, but the sensor was shot.. . Be careful with the red preheat start relay button, if you hold it in too long it will over heat and melt. My recollection is that 12v is active, as I disconnected and bypassed the ciurcut to keep the gen running. It's available from cominns for about $30.00. You can not use a std automitive tranducer, its a special S/W unit. They also can supply you with the schmetic, they were helpful to me, just make sure you have the exact model and serial number. I have the orig manual, but can't send it as I am out of town for the next week. But will do, if you still need it when I return. I check this board about 2-3 time a week. Hope this helps, Mike

[wshelton]

Had the same problem. Blown fuse 15 cents. Look for it on the generator where the start and preheat switches are.

[Bob Bradley]

Mike,
When you say that "12v is active", do you mean that the solenoid is normally "hot" while the unit is running, and then is grounded out to stop the generator?

I'll also check the fuse. Thanks for the advice, guys.

[Nonchalant1]

I have the MDJE Service Manual in my hands. It says that the solenoid is activated by + current when it is "on", lifts the plunger, and lets the fuel supply system work. When the power is turned off, the plunger drops by spring pressure against the fuel governor shutoff valve.

The solenoid has two coils. Both are energized for pulling the plunger up and when it reaches the top, it opens a set of contacts to de-energize the pull-up coil. The other coil holds the plunger up while the engine is running. Your shutdown switch simply de-energizes the hold-up coil to shut down the engine.

All it shows is one wire to the "control" and a second "lead to ground".

Test the solenoid by running a test wire straight from the battery supplying 12v + to the + terminal and - to the ground terminal. If it opens, check the ground for open ground connection. If that's OK, test the + side for power and follow it back to wherever the problem is. It could be:
1. A bad wire or connection to the solenoid.
2. A bad overheat sensor or connection.
3. A bad low oil pressure sensor.
4. A bad centrifugal switch (over-rides low oil pressure switch during startup)

I can e-mail you scanned pages for this. I'll be here today (9/7), then gone for a week.

Doug Shuman
shumans@mindspring.com
(630) 584-7919

[Nonchalant1]

Bob,

Pages e-mailed. Call me if you didn't get them.

And check that reset button before you do anything else.

Doug

[Bob Bradley]

Thanks, Doug. When all else fails, push the red button. Started right up.