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Old 09-22-2015, 07:05 AM   #1
Join Date: Apr 2015
Posts: 32
Generator needs more than 1/4 tank

Hi there. 2004 Coachmen 258DB Freedom, Onan 2.8 generator. Bought the RV used this spring with 25k miles, it's in great shape overall.

The generator is supposed to run up until the 1/4 tank level, right? With the vehicle level, ours will quit/won't run/starves for fuel even at 1/2 tank. Not very confidence-inspiring to not really know when your generator will work or not. I traced the fuel line from the generator back to where it connects into the vehicle fuel system, and was very surprised to see it is teed into the fuel fill line above the tank! You know, the big 2" diameter rubber fill line that leads from the fuel cap on the outside of the vehicle to the top of the fuel tank to fill 'er up?

Obviously if the fuel line just tees into the fuel fill line the generator would only run if there was fuel all the way up into this fuel fill area, which only happens when you actually are filling the tank.

Does anybody know how this "1/4 tank or more" situation is done on the vehicle? Is there a rubber line connected to the brass on the inside of this thing that hangs down in the tank? Basically can anyone confirm what I'm supposed to find if I take this thing apart, or does anyone know how the generator typically gets its fuel on a Class C like this? Thanks!!


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Old 09-22-2015, 07:17 AM   #2
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Maybe you're looking at a vent line? In either case here's a post with a picture of a tank lowered. I suspect many of our RV's are very similar.

Gas line to generator on Tropical

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Old 09-22-2015, 09:18 AM   #3
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Originally Posted by okcnewbie View Post
Maybe you're looking at a vent line? In either case here's a post with a picture of a tank lowered. I suspect many of our RV's are very similar.

Gas line to generator on Tropical
Thanks OKCNEWBIE. That's a very useful photo. I've been underneath for about 35 minutes now and just can't quite get a good look at the top of the tank even with an inspection mirror, so I'll start tracing back from the genset again with more care to ensure that is indeed the only line going to the gen. Will post back with my findings.
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Old 09-22-2015, 10:19 AM   #4
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The generator on MOST motor homes (thought all) has it's own fuel pickup line the fuel line goes all the way back to the tank, right next to the MAIN ENGINE fuel line, the pick up is shorter and usually cut off at the 1/4 tank per the gauge level (this may or may not be 1/4 tank, generally not).

The only thing the two systems should have in common is...
The Tank (And filler tube and tank vent) and the plate on top (normally) of the tank that holds the fuel pump (main engine only) fuel pickup (Generator) fuel gauge sending unit and float arm.

IF the generator is starving at 1/2 tank I would suspect the filter and generator fuel pump first.

HINT: on an Onan generator the fuel pump is an electric.. It makes a rapid clicking sound if you run out of fuel.

To hear it,, When you ahve not used the genny in oh a few weeks go to the generator itself when the enviorment is not noisy.. Press and hold the STOP button till the light comes on.. At this point you should hear a rapid clicking, which will soon stop.. This is the fuel pump re-filling the carb bowl.. Once the bowl is full the clicking stops.

If you run out of fuel.. it won't stop clicking.
Home is where I park it!
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Old 09-22-2015, 11:46 AM   #5
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Photos showing generator fuel pickup system on 2004 Coachmen

Hi everybody. Back from the driveway. I confirmed the line I showed was indeed the fuel line by running the generator for 10 min then clamping off the line and the gen sputtered and quit within about 5 min. I unclamped the line and after a short bit of starter operation she fired back up. So that was the fuel feed line for sure. (I had also traced it back again and confirmed that was the only line going to the gen, but the clamp/quit confirmed it).

Anyway, as others have suggested, I also replaced the fuel filter just in case it was getting clogged, but there was only 23 hours on the generator when we bought the rig. But for less than 5 bucks at the NAPA store I had a new one just in case; it was exactly the same size and made of metal like the original (NAPA #3012 if you're interested).

So, to the guts of the story. I had guessed that the fuel line connection in the fuel filler neck of the gas tank had a line that dropped down into the tank. Once I had confirmed for sure the line was the feed, I was willing to make the effort to pull that connector assembly out. Took off the hose clamps, and yep, that's exactly what it was. See the photo below of the metal pipe that then has a nylon line connected to it to drop down into the tank.

I measured the distance between the centerline of the metal pipe and the bottom of the nylon line; it was about 12.5" as you can see by the ruler in the photo. The bottom of the tank was about 14" from the CL of the fuel fill neck line, so I decided to extend the nylon line a bit since ours had shown signs of the line being quite a bit "high" of the 1/4 tank mark.

I had some slightly larger ID fuel-proof nylon line from a previous fuel injection project, and used my heat gun to soften it up and push it up on the black line. Once it cooled it was perfect. Nice tight joint that wasn't moving. (PS: NEVER use rubber fuel line for complete immersion, even if it's fuel-injection line. The rubber exterior of the line is NOT rated for continuous contact with fuel, only the inside/liner portion of the hose. So, like this project, any complete immersion in fuel must be with nylon fuel-rated plastic line).

The last thing I did was cut some little wedges out of the bottom of the line. This way there's no way the line can somehow get EXACTLY flush/seated to the bottom of the tank and shut off fuel flow. You can see this in the photo.

I ran the generator for 15 minutes or so after putting everything back together and it works fine. So now hopefully I'm further down in the tank with the pickup tube and it'll work even down to the 1/4 tank level or so. (I presume the 1/4 tank thing is so you don't run the gen during the night and run out all your fuel so you can't drive away. I can't imagine ever doing such a thing the way we use our RV, but I guess I understand the reasoning).
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Old 09-22-2015, 12:06 PM   #6
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Great job Andy! Thanks for posting the fix so that others will be able to see what you did.

It didn't make since to me how it could be the generator itself (filter or pump). I could see if you said as soon as it heats up it sputters ....

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generator, tank

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