Help mdja will not stop

mdja will not stop using stop/start switch.can't find another stop solenoid (ssc 4005 12v) .looking for ideas EXCEPT shutting off fuel to stop ..any trouble shooting suggestions welcome

What is mdja?

If you haves stuck diesel solenoid take the infer out clean and lube it.

bayview said:

What is mdja?

If you haves stuck diesel solenoid take the infer out clean and lube it.

Click to expand...

That is a model number of an Onan Generator.

Assuming you're talking about an Onan 3KW MDJA diesel Jenny?? If so, it may not be the solenoid.


(1)Are you saying it is mechanically stuck as in solenoid releases but the mechanical linkage doesn't retract


(2) Or is the solenoid stuck in the open position and won't release/retract? If the solenoid is stuck open remove the solenoid and clean it. If it won't retract when 12v is removed, but you can move the plunger up and down with your fingers then the coil inside is toast.

(3) Or It won't electrically activate?? Did you test the solenoid? if it's electrical then do this:

Sometime you may find 12 V on the wire but due to a bad connector, it may not pass enough current to activate the solenoid. So try this - Make sure you have battery ground (- Negative) at the solenoid. Then use a separate 12 volt source, (wire to the battery or some other 12 V source) remove the power wire from the solenoid and touch the 12 Volt test wire to the solenoid 12 volt electrical post. If the solenoid activates then you know the solenoid is good and the problem is in the wiring or switch. If not then the solenoid is bad.

If it's good, then you need to trace back through the wiring and switch until you reach a point where you do have 12 volts. I would start with a VOM (Volt Ohm Meter) at the switch and see if you have 12 V to the
switch. If no 12 V there, then you know the problem is before the switch. May be a broken wire or bad connector

I think that gennie uses the solenoid to cock open a valve to reduce compression. Goes through an oil pressure switch so it cranks with no compression til op shows up. That energizes solenoid, valve goes back to normal and it starts.

So I think if the solenoid failed, it would not run.

Memory is foggy here.

My memory of the DJ series is that you ave a 12 volt plunger solenoid that pushes against the fuel rack when there is no power to it, forcing the injection pump closed.

Pushing the preheat switch applied power to the glow plugs and the run relay which supplied 12 volts to the plunger solenoid, causing it to pull inwards removing pressure from the injection pump arm.

As the generator started oil pressure builds and the current for the coil of the run relay then comes through the oil pressure switch, the coolant temp switch, and a normally closed set of contacts on the stop relay.

When you wanted to stop the generator the stop switch energized the stop relay which opened the contacts carrying the current for the run relay which then dropped out.

The run relay dropping out interrupted the current flowing through the plunger solenoid causing the spring in it to push the plunger out, against the injection pump arm, shutting off fuel to the generator.

That's how I remember the circuit, but its honestly been 15 years since I had to work on one.

I tried a few things with the solenoid on my Onan which would not close to start. Used to go below and hold the rod across, it would start and the "hold" part which operates after starting still functioned, so it ran fine. I checked the Manual, it says if the solenoid plays up, replace it,(they would say that, wouldn`t they). When I got sick of visiting the ER to start the genny, I bought a new switch. Around $300!

The mdja is not like the others. It's a single cylinder started by the gen end turning into a motor. Stop solenoid is mounted on valve cover. Not like a 7.5 or 15.

Maybe OP will confirm his is like this.

Ski in NC said:

The mdja is not like the others. It's a single cylinder started by the gen end turning into a motor. Stop solenoid is mounted on valve cover. Not like a 7.5 or 15.

Maybe OP will confirm his is like this.

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OOPs, I mised that. Never worked on the single cylinder jobs. Remember vaguely reading about what you are referring to being the generator end doubles as the starter motor.

Well, there you go, so much for memory.

The start/run selinoid on the MDJ series has 2 coils in it. One is a pull in the other is a hold. The pull in has a set of points (iirc) that disengages it when the run coil takes over. Generally what happens is the pull in coil does not de-energize causing it to burn out. This is a normal problem with this setup. I have a couple of MDJF gensets in my shop but dont know if I have that part. I have been told that a fuel shut off selinoid can be installed at the pump but have not tried that. I have lots of parts if you need them.

Ski in NC said:

The mdja is not like the others. It's a single cylinder started by the gen end turning into a motor. Stop solenoid is mounted on valve cover. Not like a 7.5 or 15.

Maybe OP will confirm his is like this.

Click to expand...

Correct this MDJA Onan is started by the generator end.Thanks to all for comments.

Post a photo of the right side of the engine- area around the fuel injector pump and of the valve cover. I cant remember if there is a solenoid at the injector pump as well as the one on the valve cover.

Ski in NC said:

Post a photo of the right side of the engine- area around the fuel injector pump and of the valve cover. I cant remember if there is a solenoid at the injector pump as well as the one on the valve cover.

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This problem happened afew times last summer. I was able to shut down generator by moving the on/off switch back and forth until when in the stop position it would shut off generator. During winterizing generator it would not stop. I was informed that a rely could be bad.I installed new on/off switch thinking this was the problem,not so. Where do I look for a relay? My knowledge is very limited but I don't believe there is a solenoid at the injector pump. When I get to the boat I'll take a photo as you requested.Thanks for your help,greatly appreciated.

This may help, here is a link to the service manual covering the MDJA. But the info on the MDJA solenoid, is down about page 70. The earlier references are for the MDJB - MDJF models.

https://www.scribd.com/doc/50894910...JE-MDJF-Marine-Diesel-Genset-Engines-974-0750

while I own an onan I'm not a big fan. suggest as a last resort to stop it use a high caliber rifle and put it out of its misery

Dawdler said:

while I own an onan I'm not a big fan. suggest as a last resort to stop it use a high caliber rifle and put it out of its misery

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Dawdler, I have to find the problem preventing the Onan from stopping.Being a Onan owner have you any constructive suggestions to fix the problem?

Dave, sorry I don't have any helpful suggestions. Hoping others on this forum may lead you to a solution. Best of luck.