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Old 07-14-2018, 01:47 PM   #1
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Fuel tank plumbing for generator

My Onan Marquis 5000 generator just quit running on my last trip? So far here is what I have done. With plenty of fuel in the tank 3/4 full, I am not getting fuel to the generator from the main 75 gallon tank. I replaced the low oil shutdown sensor with a new one. I check the fuel pump replaced 6 months ago with a motorcycle battery out of the rig and it pumps real strong. I then put gas in the fuel hose from the carb to the pump and it starts and runs for a few seconds.



Then a friend suggested ( horrors of horrors) that perhaps my stand pipe in the tank that feeds the generator has fallen off. Have any of you replaced the standpipe? and if so how did you do it. My friend replaced all of the fuel hoses with new ones but I was not there at the time and now he is in Alaska. My next test step is to remove the gas line from the fuel pump blow into it and listen for bubbling in the tank. Ideas, suggestions?????


Thanks much all
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Old 07-14-2018, 01:56 PM   #2
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That was my suggestion to blow air back to the tank.
You do know that their is a fuel filter just before the generator fuel pump. Have you replaced or checked that?
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Old 07-14-2018, 02:26 PM   #3
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Yes it is new. Thanks Iggy
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Old 07-14-2018, 05:53 PM   #4
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Just had my tank down. The pickup tube for my setup is one piece. Mine runs to the bottom of the tank to the outside of the tank and then the hose attaches from there,
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Old 07-15-2018, 09:53 AM   #5
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Thanks BA, is the tube and associated plumbing bolted or screwed to the top of the tank or does the whole thing screw into a threaded flange on the top????
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Old 07-15-2018, 10:51 AM   #6
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Do the first test the easy way.

Disconnect the fuel line before the pump and blow in it.
Do you feel it bubbling?
Yes, connect the pump to that motorcycle battery again and see if it pumps fuel.
No, let the tank down and fix the pick-up tube the right way.

Cheap/suicide fix: Plug it off and put a T in the main fuel line.
(Now you can run the coach out of fuel while not going anywhere.)

Frank
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Old 07-16-2018, 06:34 AM   #7
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Quote:
Originally Posted by Magnafique View Post
Thanks BA, is the tube and associated plumbing bolted or screwed to the top of the tank or does the whole thing screw into a threaded flange on the top????
The tubes for the fuel system ( generator,main engine, return line ) go through a plate. That plate also has the wiring going through it. So it all goes through the top of the tank and then there is a "O" ring that creates the seal between the plate and the tank. After it is set down on the tank there is a locking ring that sets into some tangs ( on the tank )and twists to seal down the whole plate. ( I hope I explained it good enough )
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Old 07-16-2018, 03:26 PM   #8
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Disconnect the fuel line at the generator fuel pump and put a little air pressure in to the fuel tank and see if you get air or fuel out of the fuel line. This might be an easier way to test the pickup tube.
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Old 07-17-2018, 09:34 AM   #9
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Still another idea is to pull the fuel line off of the generator fuel pump and try putting a funnel in it and pour some gas into it and see if there is any coming out of the hose somewhere between there and the fuel tank.
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Old 07-17-2018, 08:21 PM   #10
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Your 97 should be similar to my 99.. I installed a new fuel pump assembly in the tank this spring. You can look at the photos and see how the genny pickup is done.. It a third pipe on the pump assembly..


http://www.1999southwind.com/f53-replace-fuel-pump/


QUESTION..

You said you hooked the genny pump up to a motorcycle battery and it ran strong... Did you see if it was actually pumping fuel, i.e. disconnect the fuel line at the carb and see if the pump is pumping fuel??

If its not pumping fuel, disconnect the fuel pumps supply hose (the hose that comes from the tank), and connect a hose to the fuel pump input and drop the other end in a gas can. See if the pump will suck fuel out of a can..
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Old 07-22-2018, 12:31 AM   #11
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Quote:
Originally Posted by Magnafique View Post
My Onan Marquis 5000 generator just quit running on my last trip? So far here is what I have done. With plenty of fuel in the tank 3/4 full, I am not getting fuel to the generator from the main 75 gallon tank. I replaced the low oil shutdown sensor with a new one. I check the fuel pump replaced 6 months ago with a motorcycle battery out of the rig and it pumps real strong. I then put gas in the fuel hose from the carb to the pump and it starts and runs for a few seconds.



Then a friend suggested ( horrors of horrors) that perhaps my stand pipe in the tank that feeds the generator has fallen off. Have any of you replaced the standpipe? and if so how did you do it. My friend replaced all of the fuel hoses with new ones but I was not there at the time and now he is in Alaska. My next test step is to remove the gas line from the fuel pump blow into it and listen for bubbling in the tank. Ideas, suggestions?????


Thanks much all
I would more SUSPECT your 6-mo old fuel pump has failed. TODAY, I replaced my fuel pump and ran GREAT under load for 2-hours test with no issue; did still have to rock the altitude adjustment 15-20-times to settle down the surging when first started. ISSUE HAD BEEN that it would die after 20-30-minutes under load and not restart until it cooled down 15-30-min. Gen is an (20-y/o) 220-hrs ONAN EMERALD PLUS BGE, spec-P, Fuel Pump appears to have been original. This symptom is typical for what I have experienced w/ several vehicles. MY NEW PUMP is a NON-Onan, but only $28 (Amazon) vs $100+ for OEM. p.s. I would fear pressurizing tank by blowing back, as that will send a spray of fuel back at you ... If you attempt, at least have tank cap OFF during testing, and no flames or hot engine surfaces, with extinguisher handy.
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Old 07-22-2018, 04:15 AM   #12
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Hi gang,

Have you checked the voltage getting to the fuel pump?

It must be a minimum of 9.6 volts (while cranking the starter). Might need an extra pair of hands.

Dave
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