Onan diesel generator cranking but not starting

[153stars]

The usual culprit already mentioned ,right off is fuel pump. Do you hear the clicking sound of the fuel pump pressurizing the system. You might have glow plug issue if has started giving you problems in the cold. There are service and diognostic manuals online ,with fairly easy to understand flowcharts and tests. Of course much easier repairs on genny that slides out . If you open the box or drop a genny it's a good time to inspect, test items amp preemptively change wear items.

[oceansailor]

Originally Posted by txcpl

Our generator takes a while to crank over and start. I have had to hold the start switch down for nearly 1 minute to get it to start once. Without fault codes to begin your search, I have no other ideas.

Thanks for your response. Mine usually starts in 2-3 seconds, but I've tried cranking the full 30 (that's the limit per the above manual) several times. And yeah, not having any codes is annoying - but again, the manual says they're shown "following a fault shutdown", and since it's not starting at all, I've got nothing to work with. Guess I'll be breaking out the toolbox this weekend!

[oceansailor]

Originally Posted by 153stars

The usual culprit already mentioned ,right off is fuel pump. Do you hear the clicking sound of the fuel pump pressurizing the system.

Yep, I do hear it. However, I just tried it again, and now I'm not hearing it slow down/come up to pressure the way it should - so despite the fuel gauge showing half a tank, I may have a supply problem (or a blown diaphragm; I hope not.) Moving the RV would be a pain, but I should be able to borrow some fuel jugs from my neighbors in addition to my own and eliminate that possibility.

You might have glow plug issue if has started giving you problems in the cold.

That was a side discussion about ether, not relevant to my current situation. The temps here are in the high 80s.

There are service and diognostic manuals online ,with fairly easy to understand flowcharts and tests. Of course much easier repairs on genny that slides out . If you open the box or drop a genny it's a good time to inspect, test items amp preemptively change wear items.

Mine slides out, which is pretty wonderful. After 20 years of living on a sailboat and the acrobatics that engine work requires on most of them, it almost feels like cheating!

Thanks for your suggestions.

[oceansailor]

Originally Posted by Argosy

It sounds like it's bogging down because the ether detonates before TDC. It's firing, just not when it should.

Thanks - that makes sense! It also supports the idea of a fuel supply problem.

The engine is a 3 cyl kubota. My experience with them is a few seconds of glow plug is a lot better than a few seconds of cranking. They're small and normally aspirated, any heat you can put in the head or cylinder does a lot of good to get them to fire off, even in fairly warm weather.

Since I rarely use this genny, I always prime for ~10 seconds the first time around. I'm guessing that should also actuate the glow plugs. If I have to crack it open, I'll check the fuse, though.

It's really hard to say there's a proper way to use ether to start diesels today.

I find it useful in two situations: diagnostics, and after fuel filter changes on the Cummins ISC in this coach. It is absolutely intolerant of air in the system, and despite filling the filters, running the prime cycle over and over, etc. it simply will not start without a quick burst of ether. I've even thought of adding an electric lift pump to the system, but haven't done it so far. I shouldn't complain - there are only a few annoyances of that sort in this coach, it's pretty well designed otherwise - but it's a fairly major one. Fuel supply is very important to diesels, especially modern ones.

[TandW]

If ether doesn't make it pop you have low compression. Perhaps a stuck valve.

[Jameson223]

You may try silicone spray lubricant instead of starting fluid or WD-40. At one point in my past, I used to drive buses, and the diesel mechanics in our garage always used silicone spray when a bus ran out of fuel and they needed to get it going again.

[Argosy]

If you've got half a tank of fuel it's possible the fuel level is below the pickup tube. Most motor homes need between 1/4 and 1/2 tank for the generator to run.

[153stars]

Forgot to mention bad fuel hose, can suck air on supply side. The hoses used are not to par with MH engine one. Just plain reinforced rubber fuel lines.

[oceansailor]

Originally Posted by Argosy

If you've got half a tank of fuel it's possible the fuel level is below the pickup tube. Most motor homes need between 1/4 and 1/2 tank for the generator to run.

Aaaaand... you, sir, found the answer to the $64,000 question!

At first, I didn't think that could be it because I remembered running this genny when the fuel indicator was showing ~1/4, so it should have run fine at 1/2. However, I went ahead and took two trips to a local gas station - none of my neighbors had any diesel jugs I could borrow, so I only had my own pair - and added 20 gallons to the tank. One long prime later, VOOM! - it fired right up.

At this point, I'm thinking that either the fuel gauge or the tank sensor is going. Already took a look at the wired connections on top of the tank - nope, they're clean, dry, and tight... so I guess I'll check the ground at the gauge, and order another one from Amazon if needed. I only hope it's not the sensor, because dropping the tank on this thing would be a big hassle.

Thanks very much to everyone who's taken the time to post - much appreciated!

[Argosy]

I'm glad it was an easy fix, and free even.


Thank you for letting us know the solution. It helps immensely in the future when others come here to use this as a resource.

[rssnape]

So if your fuel pump is starting to lose prime, it may have once started at a 1/2 but now needs more to allow the fuel to reach the pump. A pump will only create so much lift, and once it leaks down from a leaky pump. It may struggle to get the fuel from further down in the tank.

You can try running it on your next trip and if it cuts off at 1/2 tank, it’s likely your fuel gage. If runs on down to 1/4 and then fails to start the next morning, likely your fuel pump.

[153stars]

You can try sticking the tank. I think hot water trick will work on side if tank if the tank bay door opens. Lots of owners have issues with Centroid fuel sender ,some solutions are just cleaning it or re-calibrating it. Not really too costly to replace either , I think $270 for longer units. I had bad Staycon crimps on my wires. Mine is old style with potentiometers to calibrate. Couldn't get perfect calibration empty to full. II chose highly accurate less than half. Not going to bother me difference between 175-200 gallons. Rather know when close to run out with genny and AH instead.
I agree tired pump looses lift.You might want to go ahead and get a spare lined up.

[oceansailor]

Originally Posted by 153stars

You can try sticking the tank. I think hot water trick will work on side if tank if the tank bay door opens.

I used a bead chain with a fishing weight on the end to check it. The gauge is definitely off; given the current level, it must have been well under a quarter tank before I added more. Not a comfortable realization, given that my last trip was a last-minute dash to dodge Hurricane Ian; running out of fuel in the middle of that, with the 'cane bearing down, would have been... unpleasant.

Lots of owners have issues with Centroid fuel sender ,some solutions are just cleaning it or re-calibrating it. Not really too costly to replace either , I think $270 for longer units.

Excellent info - thank you! I just found a Centroid troubleshooting sheet for Monacos -

http://www.centroidproducts.com/zTro...tingMonaco.pdf

- and will check that out tomorrow. As I've mentioned, I checked the wiring, and it looks solid, but it may have gone out of adjustment - or the problem may be at the gauge. (Relevant valuable lesson from my experience: most people would be surprised at how hard you can/should pull a crimped connection to test it; most don't pull nearly hard enough.) Since trying a new gauge is much easier than getting to the sender, that'll be my next step - assuming the voltages at the sender look reasonable.

I agree tired pump looses lift.You might want to go ahead and get a spare lined up.

Oh, it's pretty clear that the problem this time was the low fuel level - but I'll certainly keep that in mind. I'm also going to wait for a couple of days and rerun it just to see if it loses prime, or even takes a long time to re-prime. The genny isn't something I run a whole lot, but it's good to have it when I do want it.

[153stars]

I have heard mostly of issues with sender not the gauge. They can get gunked up and just clean can help. Clean all connections. Inspect crimp connectors. I have found numerous bad Staycon crimps or wires just pulled out during other work.My doors on each side of tank open with just a couple bolts . The sender is easily accessed . If it's still working at all, you should just clean the tube and connections and recalibrate it. I'm not sure of what year they went from adjustment pots and resistive to capacitance type sender with more of a sequential calibration procedure. Getting into dash cluster is not what I would advise right off.