No fuel to genny

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Dzimbric

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Joined
Dec 30, 2019
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30
I have a new to me ?98 HR Endeavor on a Ford chassis.  It has not been used or started in over a year.  I have it running, resolved issues with the jacks and filled the fuel tank. It runs and goes down the road. 
The Onan 5500 won?t start, does anyone know how the supervisory circuit is set up prevents the generator from running when the fuel tank is below 1/4?  Is there solenoid valve that may be stuck closed?
 
There is no supervisory circuit, the generator's fuel pickup only extends 3/4 of the way into the tank.  If the tank is less than 1/4 full the pickup just sucks air.

It's possible the flexible fuel line running from the outlet at the top of the fuel tank is cracked.  Unlike the main engine where the fuel pump is in the tank, the generator's fuel pump is located at the generator and has to suck fuel from the tank.

It's like drinking through a straw.  The fuel line exits from the top of the tank and any leaks in the line will break the suction and cause fuel to drain back into the tank instead of leaking out through the hole.

An easy way to confirm if the problem is in the fuel line is to disconnect it at the generator and substitute a flexible line extending into a gas can.  If the generator's fuel pump then pumps fuel, you have a problem between there and the fuel tank.

If the generator has sat for a while, another common problem is old fuel may have varnished and plugged up the carburetor jets, meaning you'll have to clean or replace the carburetor.
 
Just to clarify, it is designed to leave 1/4 tank remaining so the gen won't run the tank dry and leave you stranded.
 
Well that sure makes it simple.  I?ll put my mighty vac on the line and see if I can draw fuel from the tank.
 
Don't count on the vac being an adequate test. I once had vac leaks that would not suck from a half tank, but worked just fine if the tank was full. That a very low pressure pump on the generator. Do the test as recommended above.

Ernie
 
On a freightliner chassis a second fuel filter was often installed on the chassis frame between the wheels - hard to find and often coated with undercoat (look for a big bump as you trace the fuel line). The final RV manufacturer would put on a second filter where it can be found.

If I recall, you did not mention changing fuel filter - I'd certainly start there. Plus, have the "heads up" that there could be two - one of them hard to find, and if you have that extra one, bypass it or move it to where you can get at it.

Just to confuse the issue - I think our Onan has a low oil override so it won't start... (vague memory from someone's post in the past).

Good luck and let us know...
 
Arch Hoagland said:
Are you holding down on the prime switch before trying to start?
Click to expand...

Good point - also, wonder if OP is only using the remote start switch in the cab - or using the switch mounted ON the Onan... (we have one in the cab).
 
No the genset is a Onan Marquis 5500 and it does not have a prime switch.  What it does have is electric fuel pump mounted on the back of the genset with a little bitty failed 12v horn relay mounted on the back of the air box.  This location is optimal because it requires you to remove the carburetor so you can access the little screw inside the breather tube that you have to remove so you can get the airbox off. The best part of removing the carburetor is damaging the gaskets so you can practice your gasket making skills.
So I replaced the relay and have fuel at the carburetor.  Once I find the missing nut I can finish assembling it to see if it will start.
Their is a lot of information available on the Onan forum and I will keep spare relay and fuel pump on rg.
 
OP said: "No the genset is a Onan Marquis 5500 and it does not have a prime switch."


I have an Onan Marquis 5500 and the way you prime it is press the bottom portion of the start switch for about 30 seconds. Otherwise it won't start without cranking for a long time.

Do you have a start switch on the dash of your coach or just on the generator itself?
 
I changed the oil; date on filter was 9/15/10, replaced the plugs and found a bad fuel pump relay.
I replaced the relay and have fuel in the bowl.  I have spark and gasoline vapor comes out the spark plug port when I cranked it to see if I have spark.
i held down the off switch to prime it several times but will try it some more.  I removed and cleaned the bowl too.
Is it time for a new carburetor?  I sure hate spending $300 if I don?t have to.
 
The STOP button (Bottom of start) is also prime. Held for 30 seconds or more.  If you are outside using the generator's on-board switch you SHOULD hear the pump CLICK after you hold the button for like 30 seconds. .Hold it a bit longer then tap start.  Just a short tap (like 1/2 to 1 second) then count to 10 or so and press again, longer this time. Seem to work best for me.
 
If you're seeing visible fuel vapor coming out the spark plug hole, there's a good chance the cylinder is flooding with too much fuel.  Make sure the choke isn't stuck on, if it's open you're looking at a carburetor replacement or disassembly and cleaning.
 
Dzimbric said:
i held down the off switch to prime it several times but will try it some more.  I removed and cleaned the bowl too.
Is it time for a new carburetor?  I sure hate spending $300 if I don?t have to.
Click to expand...

Bought one on line for $60.00.  Installs in an hour.  Now it works like a charm.  Don't know if it will last as long as the $300 Onan OEM carb, but I'll take my chances. 
 
I had a guy who knows engines pretty good. He is a retired small motor mechanic and we found no spark.  When I connected the test light I had power on on one of two coil terminals. When I lifted the oil level switch lead I had power on both terminals when cranking. The test light remained bright and did not go bright/dim/brighT.  The genset has not been started for at least a year. Failed ignition module or coil?

After looking at a Onan site O may have disconnected the ignition control module.  Does anyone have a schematic?
 
Get a can of starting fluid and spray it a second at a time into the carb while cranking. It should at least make a different sound while cranking, as if it's trying to start. If nothing, you have no spark so go from there. That is the situation I'm in with an Onan Emerald that hasn't run in 8 years. Just pulled the plugs and they were carbon fouled. Cleaned them up and will try again.

http://www.fototime.com/DCA407078BF6FBE/large.jpg
 
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