'94 HR Imperial DP - Onan Gen Not Running

[kurt-o-matic]

Hey all,

First-time motorhome owner with a 36' 1994 HR Imperial Class A. The rig in general is in great shape, and the genny was firing up and running fine a couple of months ago, but now isn't running.

I don't have all the manuals, and I'm still trying to ID this specific genset. I believe its likely to be a 3-cylinder 7500W unit. I haven't found the serial number or ID plate yet; I have to store it out in the country, and can't get to it easily to spend time on it myself.

In any case, the generator had been working fine; however, I've only had the rig since mid-March and I didn't really need the generator during the Spring. Now that it's hot, I'm needing the genny, and it's not cooperating.

The tricky bit here is the Onan will start and run as long as I hold the starter down. As soon as I let go, it will stumble and die. This is very consistent. Fires right up every time, just won't stay running on it's own.

Starting-but-not-running seems to be a little usual, and it's hard to google search this; most of the hits I get refer to non-starting scenarios.

However, I did see one idea that I wanted to get opinions on. I saw a suggestion elsewhere to hold down the priming side of the switch for way longer than the usual sub-30 second cycle (something like 2 minutes) in order to pull fuel all the way through the lines after running low on diesel.

After the first trip with the MH (driving home over two days), I left the coach in storage with only a 1/4 tank of diesel. Now I am aware that the generator won't run on anything less than a quarter tank. I'm pretty sure I never attempted to start the genny with this little fuel; I certainly never had this current failure mode at that time. I subsequently put the rig in a shop for a few weeks; it's possible they ran the generator since I asked them to look everything over.

When I recently took the Rambler on a camping trip, I waited until I filled the tank before attempting to play with genny. This is when I first noticed the problem. We left town anyway, and I really only missed the roof A/C on the way home from the trip. However, I'm not going anywhere in July without the generator working.

I know a fair bit about classic carbureted V8s and such, but I am a total noob with RVs, diesels, and generators specifically. I'm not even sure precisely what the 'priming' side of the switch does. Is the idea of holding this down for longer than 30 seconds actually a thing? Does the starting loop have a different fuel supply than normal operation?

[NHRA225]

In order to receive an intelligent response we need the Model off the Genny, in the early 90's it could be one of 2 styles.
An Onan DKDFJ -On the Noisy side or a Onan HDKAJ series Quiet Diesel.
Here is the DKDFJ series

[kurt-o-matic]

Thanks so much for your reply, Chuck. That helped tremendously!

The pic was very useful--it's clear that I am looking at a DKD with a Kubota. Is that genny on a slide-out tray? Jealous!

I've attached a pic of both sides of my generator I took when I bought the rig. Also, no one would fairly describe this generator as 'quiet'.

So.., armed with this knowledge I've done some more research and I'm certainly less clueless than when I posted this thread last night. Whew!

Because that question really was clueless, LOL!

Alright, so it appears there is at least one pattern of behavior that fits my symptoms, where the 'hold in' solenoid function does not activate after the 'pull in' function is released at the starter switch. In other words, this looks like an electrical control problem, and is not likely to be fuel (or even engine) related.

I've got the rig scheduled to go in the shop next Tuesday. I was hoping this was some dumb operator error on my part that I could correct myself. At least I now have a very good idea what the model on this is, and can reason about a little bit better.

[johnhicks]

Check for low oil or MH not level enough causing low oil.

[NHRA225]

Lucky me as mine slides out the front for easy service work.'Now onward : Besides the obvious of all the fluids at full marks there typically a couple of possibilities as to why it won't stay running.
before we get to that there are 2 switches that must function to start -the 1st is the the glow plug rocker switch which heats the Glow plugs in providing heat in the cylinders and that switch should Never be used for more than 15 seconds prior to starting.
The second switch is the start and shutoff - self explanatory. when you hit the start sw it actives the Injector pump pull in plunger/solenoid and at the same time it activates the fuel pump, there are 2 terminals behind the plunger solenoid one is ground and the other B+ activated from a relay in your control box through circuit K-14- clearly marked. That relay can go bad and its easy to replace.
Check the wire connections behind the Plunger Solenoid 1st,
Here are a couple of pictures to get you started.If your taking it to a certified Onan service center @ $110 an hour these simple checks could cave you some $$.

[kurt-o-matic]

Thanks guys. The rig is stored an hour's drive away, unfortunately, which is a different problem I'll need to consider another time. But I can definitely get out there to check some of this soon, just not likely to be tonight.

Here is a pic of front of the genny showing the controls. There is a 35-amp breaker box above the engine, and the control box is mounted on the upper left corner. Those are all the electrical controls I know of. There is labeling on the control box for preheat, but no distinct preheat rocker.

The rig is in a covered storage spot, and should be very close to level (plus, I've attempted to start up the generator when the coach was up on its jacks). I'll check the fluids on the genny as soon as I can get out there; that should be easy enough. Getting to the back of the plunger solenoid will be a pain. At least the control box is right there in the access opening.

[NHRA225]

That thing is tucked in there!
Let us know if you find anything.

[Wdebarmore]

I have two start switches. One on the dash and one in the kitchen. Sometimes when I turn off the generator using the switch on the dash, the switch sticks a bit and doesn't go all the way down. When it does this, if I try to start it using the switch in the kitchen, I have to hold it down to keep it running. Go push the dash switch all the way to the off position, and the kitchen switch works fine... Did that make any sense ?

[kurt-o-matic]

Originally Posted by Wdebarmore

I have two start switches. One on the dash and one in the kitchen. Sometimes when I turn off the generator using the switch on the dash, the switch sticks a bit and doesn't go all the way down. When it does this, if I try to start it using the switch in the kitchen, I have to hold it down to keep it running. Go push the dash switch all the way to the off position, and the kitchen switch works fine... Did that make any sense ?

Yes, but I only have switches on the dash and on the genny itself. I can totally see how that problem mode could occur, though. In my case, I get the same behavior whether I try to start the generator from the front or the cabin.

Thanks for the tip!

---

I'm going out to check on the rig tonight. I'll check the oil and try to observe the plunger action at the very least.

I've spent some quality time with the Onan manual and parts catalog, and I feel like I have a better handle on the electronic controls for this unit. I went ahead and ordered a replacement K14 relay just on principal, because they aren't expensive. I also found an aftermarket replacement monitor board from Flight Systems that has a good reputation. At $160, it's almost an impulse buy just to have on hand, but I think I should at least check the oil and any other easy sanity checks I can make before pulling the trigger on that.

[NHRA225]

Sounds like a plan ! Keep in touch !

[kurt-o-matic]

The oil is great; the level is perfect and it's very clean. The previous owner was very good about maintenance.

I played around with both rocker switches (in the cab and on the control box), and everything is working correctly in that regard. The solenoid is really buried back there, and is practically inaccessible without starting a serious disassembly effort somewhere.

At this point I'm going to cross my fingers and bet on the control box, which has much better access. Also, the problem has occurred as a binary failure mode, which is consistent with a relay or board failure. I've ordered a replacement control board and I'm working to remove the control box.

Regarding the cabling plugged into the back of the control box: how are these connectors fixed? Are they strictly an interference fit and you just wiggle them loose, or is there some kind of retainer mechanism in the form of a clip or threading? I can't the see the back of the box and can barely reach the cabling. Even once the box is loose, I'm expecting the slack in the cables to be minimal.

[NHRA225]

There are 3 plugs on the outside of mine, 1 is a smaller 6 prong- square that has pinch clips and the other 2 -Cannon style plugs- again mine might be different than yours ! The Cannon plugs have a twist to unlock and pull out connector .
Do you have the Board Part number from Flight Systems ?

[kurt-o-matic]

Originally Posted by NHRA225

Do you have the Board Part number from Flight Systems ?

The Onan part number for the monitor control board is 300-2604. The documentation from Onan and the physical layout of my generator are all consistent, so I'm fairly confident of that part number.

https://www.flightsystems.com/p-56-0260-00.html

[NHRA225]

Thanks ! Same number my book shows.