Generator fuel line

[Utah-Clay]

The PO on my 1992 Horizon-ST put a fuel cut off on the generator fuel line because he said when driving it would smell like gas. I checked it out and if I left it in the "on" position gas is being pushed to the generator. After reading several posts I thought it might be t'eed  on the FI main line allowing the pump to pressurize the line. Crawling underneath and referencing the service manual I see that it is t'eed into the No. 2 fuel hose, the lower small line. My 92 has a main line which is larger and 2 smaller lines beneath it. This line goes into the tank separate from the cap over the FI pump that includes the large line and the upper small return line.

I don't know what this lower line does, after the T it follows the other return line to the front. I lose it under the engine. It maybe another return line? Why would it have pressure while driving? I would prefer that  I don't have to switch the fuel on and off with use. Thoughts?

[Maineah]

The truck should have 3 lines, pressure,return and evap. None of those should be used for a generator generally there is a stab in type of tap that connects to the fuel tank at about 3/4 so the generator won't run the tank dry. If there is any restriction on the return line it will affect the fuel pressure. If the "T" is in the pressure line the line to the generator will be subjected to around 35 psi little over the top for something designed to run at about 3 psi. This is something you really need to get to the bottom of if it's full pressure some thing is going to leak and eventually break the pumps deliver a lot of fuel fast most of it is returned to the tank via the return line if it doesn't it going on the ground and everywhere around the leak. 

 

[Utah-Clay]

It is not on the pressure line but on the smaller line that connects directly to the top of the tank, not in the access cap to the pump. 

 

[WME]

My Escaper genset ran fine with the T in the return line. There is no pressure on that line. The return line goes into the tank to the 3/4 level.

The main FI line in a major nono. I'm unsure about the evap line, but I think it goes into just the top of the tank so the genset wouldn't run long if it was there.

Jackup the RV and see if you can see if any clamp is leaking. USE JACK STANDS

 

[Utah-Clay]

On 5/2/2019 at 6:03 PM, jjrbus said:

 

 

Edited May 19, 2019 by Utah-Clay

[Utah-Clay]

The lines are tight and leak free and the Onan Generator runs great. It is just the gas smell when driving that is the problem. I wonder if there is enough pressure on the return line that it is forcing fuel into the generator carb and leaking out?

[Utah-Clay]

Oops, take it back, the line that has the t is the fuel return line. That makes sense but still doesn't explain the gas leaking into the generator. 

[WME]

There is no pressure on the return line...unless the PO misaligned the T when it was installed and peeled off a chunk of rubber hose and that is blocking part of the return line.

The ONAN has an electric fuel pump is it OFF when going down the road?

Weird stuff. Remove the fuel line from the ONAN carb stick it in a bottle and have someone start the Truck engine and see what comes out. if you get fuel, remove the Toys gas cap and see what happens. A correctly working tank venting system will have a vacuum in it when the truck is running (the hissing when you loosen the gas cap). If it is building pressure that's not good.

[Utah-Clay]

17 hours ago, WME said:

There is no pressure on the return line...unless the PO misaligned the T when it was installed and peeled off a chunk of rubber hose and that is blocking part of the return line.

The ONAN has an electric fuel pump is it OFF when going down the road?

Weird stuff. Remove the fuel line from the ONAN carb stick it in a bottle and have someone start the Truck engine and see what comes out. if you get fuel, remove the Toys gas cap and see what happens. A correctly working tank venting system will have a vacuum in it when the truck is running (the hissing when you loosen the gas cap). If it is building pressure that's not good.

Yes it has an onboard fuel pump, not sure if it is electric or vacuum.

I think the idea of disconnecting the fuel line to the generator and running the engine is a stellar troubleshooting idea. I may have a restriction that is allowing the pressure on the return line to push fuel into the generator carb. Probably have a worn needle and seat in that itty bitty carb as well. Probably just stick with the fuel cutoff, it seems messing with a good running generator is like waking a sleeping baby.

[fred heath]

I have the Onan 2800. It has an internal electricity operated fuel pump. Most fuel pumps are “flow through “ which means there is no gasoline shutoff to the carburetor. You could install a manual shutoff valve somewhere near the generator. I have a small POL approved ball valve installed on mine. Makes it a convenient and safe way when I have to to do any service on my genset.

[Utah-Clay]

I removed the fuel line from the generator and when the vehicle engine is running fuel is pushed through this hose, it is not under a tremendous amount of pressure but is flowing out. This leads me to a couple of thoughts. a) there is an obstruction in the line to the tank side of the tee b) since the fuel return is under the gas tank level the pressure needed to flow into the tank is enough that it is pushing to the generator as well.

 

I will just leave the fuel shut off in place and manually turn it on and off when I need to use the generator. Maybe someday relocate it to a more accessible location or find a cable actuated valve so I can turn it on and off from the cabin.

[Maineah]

Directly from Onan "The generator set and propulsion engine fuel supply and return lines must not be interconnected". I also think some states will ding you for tampering with evap control and fuel lines. (emission controls). Here is the logic, the MH fuel pump delivers far more fuel than the engine needs by about 50% it is regulated to around 35 psi so close to 50% must be returned to the fuel tank. In a perfect world the restrictions would be minor. Even the level of fuel in the tank will have some effect. You add any kind of damage or restriction (too small a "T") the pressure of the returned fuel is going to rise. The gen set runs around 3 psi so you can see where this is going it is not capable of dealing with much fuel pressure. I ran into this several years ago with a BMW it was towed to my shop it did run but barely the crankcase was full of gasoline and the fuel pressure was in the high 60 psi range the cause was a smashed return line under the vehicle. So anything "T'ed" into the return would be subjected to that kind of pressure.