Generator Stalls only while Driving

[Safari_Sam]

Hi everyone! My first post. I bought a 1999 Safari Zanzibar and I am trying to solve a mystery. Auto transfer switch kept dropping the generator power so I bypassed the switch. Now, Onan 6500 propane genset purrs like a kitten while parked and running two rooftop ACs and the convection oven (total draw is 40 amps on both legs combined and 113 volts on each leg). However, the genset stalls when on the road. I noticed it occurred each time I came to a stop (three times I restarted it). After the third stop, I restarted it and turned on the front rooftop AC. The AC was rattling as if not getting enough power. I checked the genset and it was full throttle which is not normal for just one AC unit. Seems like a fuel problem to me. The propane fuel filter is not a replaceable type. It has to be rebuilt with new o-rings. Instead, I had sprayed carb cleaner into the air intake and put new sparkplugs. After that, it ran perfect parked. I wonder if liquid propane is sloshing in the tank when coming to a stop and not feeding fuel sufficiently??? The tank is 2/3 full. Since the governor had the throttle full open on the last test with one AC unit, seems it wasn't getting the fuel it needed. I'm sure it was not designed to allow a slosh problem but at 16 years old, it could be a malfunction in the delivery of fuel. I'm just not sure why it happens only while driving. I am out of ideas.:h

[Kayteg1]

The liquid feed of propane has bad wrap from decades.
I had propane forklift that had heat exchanger for the propane using engine coolant.
From my observation lot of generators do have zigzag propane tubing running around the engine head for heat exchanger.
Add to it that sucking propane from bottom of the tank you are also sucking all the dirt, that vapor appliances will never see.
So not even going into what cost present problem, converting the feed from liquid to vapor would be suggested rather sooner than later.

[Safari_Sam]

Thanks for the replies folks. Oil level is at the full mark so I have ruled out low oil. Since it starts right up after stalling, I don't think it would be an overheating issue. I am still leaning toward a fuel starvation theory since it was struggling to run just one AC at full throttle when I parked. The next morning, it ran both ACs again and still wasn't at full throttle. I don't have any fuel issues with appliances but those run on vapor while the gen runs on liquid propane I believe. That makes me wonder if there is a malfunction in the liquid supply system from the ASME tank. I don't know how to test that theory however.

[kenbert]

I had the same problem, turned out to be low oil. filled oil to proper level and never did it again. Oil level was fine when parked, but when driving it would shut off when I came to a stop, or on a sharp turn.

[mowdoc]

I just found, and looked at, a service manual. The Onan I have, and prolly yours too, is air cooled and has no temp sensor or way to shut down engine because of heat. The switch we are putting jumpers on is the oil pressure switch, not an oil level switch. Cutting them and splicing them together on the engine side of the cut is simply bypassing them as though they were not there. The controller does not know they are absent.

You will see these two small white wires near the lower part of the engine (sump). They are connected to a screw in switch that is sticking out the side of the casting.

I cut mine and put spade plugs on them so I can bypass the switch for travel and then plug them in to use the switch for camping. So far - so good.

[Kayteg1]

I would also observe temperatures.
Air flow on moving motorhomes can have pretty strange pattern and I would not be surprised if engine heat gets to generator compartment and overheat sensor shuts it down.

[Rick_Jay]

mowdoc,

I can attest to your diagnosis. I generally top-off the oil level before every trip to make sure it's right at the full line.

What I have also found is to use the thickest oil recommended for the temperature range expected. My generator manual says 5W-30 is OK, but I found on hot days the generator would frequently cut-off after hitting a large pothole or hard braking. When I switched to straight 30W oil (also recommended) the problem lessened to the point where it is rarely experienced.

Now, I'm not in Las Vegas, so you are experiencing a whole new level of "hot" compared to East Coast temps, so I'm guessing the oil will be even hotter (thinner).

On my "to do" list is to make a little circuit which will filter the low-oil switch signal such that the low oil condition has to be constant for a short period (maybe a second or so?) before sending the shut-down signal. Should be pretty easy to wire up. But honestly, so far, using the straight 30 weight and keeping the oil topped off has pushed this project to the back burner. Now....if and when we start travelling out your way, I may re-address the need. 🙂

~Rick

[mowdoc]

I have zero experience with LP fired gennys but have had three gasoline Onan gensets on my RVs. I suspect the LP units are identical to gasoline ones except the fuel system.

OK, the late model coaches with Onan gas gennys are having same symptoms as you are having. They stop running on hard braking and some turns. The units I speak of all have genny mounted on driver side of coach.

What we have learned is the oil level slops to the front of the pan during quick stops and the low oil level shut down switch is being activated. We have began slightly overfilling the oil level just a hair above the full mark on the dip stick and this has fixed most problems. You can still trigger the shut down with hard braking but the problem is much better with extra oil in the engine.

Some of us have placed jumper wires on the low level switch to bypass it but we have given up the protection Onan built into the genny for low oil level in doing so. We must keep a close eye on oil level this way but our gennys never shut down on the road (because of hard brakes or turning)

[Effy]

wa8yxm wrote:
In days of old Fuel tanks were vented,simply vented.. Then came the EPA and now if it is Gasoline (not sure about Diesel, or rather no clue about diesel) the gas cap is valved so it should admit air but not let fuel vapor out...

And in some cases it is just plain sealed and the tank vents.. by other methods and routes.

I have heard of cases where the main engine sucked fuel fast enough that a slight vacuum built up in the tank,, JUST enough that the generator fuel pump coudl not over come it and the genny starved and stalled.

Per the OP it's an LP genset.

[wa8yxm]

In days of old Fuel tanks were vented,simply vented.. Then came the EPA and now if it is Gasoline (not sure about Diesel, or rather no clue about diesel) the gas cap is valved so it should admit air but not let fuel vapor out...

And in some cases it is just plain sealed and the tank vents.. by other methods and routes.

I have heard of cases where the main engine sucked fuel fast enough that a slight vacuum built up in the tank,, JUST enough that the generator fuel pump coudl not over come it and the genny starved and stalled.

[ScottG]

Sounds like perhaps something is vibration sensitive.
I would start by jarring or vibrating everything you can in an effort to reproduce the failure. You can even use a vibrating sander (no sandpaper of course) to vibe parts. I used to do a lot of this sort of things with avionics systems.

[MrWizard]

I don't think it's sloshing in the tank
I don't know your current configuration
The OEM configuration is liquid feed, the tank has two valves top one is vapor for appliances and heater, bottom valve is liquid for the generator
Some owners changed the liquid feed system over to a vapor feed system
Honestly I don't know which one is better, or if it makes a major difference
Ours never gave us any trouble that way

But a 2/3 tank should have plenty of fuel
I would investigate the propane line routing, maybe it has been moved and engine heat is affecting it
This reminds me the 5.9 engine exhaust is under the generator
If something on this exhaust has been replaced, this might be a problem