Onan generator stops after a few minutes

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ELVERDA

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Aug 4, 2014
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Generator  has been rebuilt. It ran fine for about a year and now after about 15 minutes it surges like it cannot get enough fuel and quits. I have replaced the fuel filter with no change. This is a Onan 5000.

Thanks for any help

Elverda
 
I also have an Onan 5000.  It has 560 hours and was serviced at 500 by the previous owner.  Today it started with a little hesitation, ran roughly for about 15 seconds before it quit, and now it won't restart.  It's catching some fire and popping and even kicking over on its own a few times but won't start...like it's not getting enough fuel.  So like ELVERDA I changed the fuel filter but that didn't make any difference.

I figured if I added my very similar headache to the thread, we might be able to eventually help each other.  :)
 
onan carburators are very problematic after they have been sitting without running for extended time fuel gums up fuel passages. onan only recommends replacement but some have some haven't has success cleaning their existing carburetor.
if capable try this test, just know the repair fluid he uses no longer exists.
https://www.youtube.com/watch?v=CLLI359w2RM
 
You can accomplish the same thing using Seafoam. They do make a spray carb cleaner, or you can use a spray bottle and spray inside. I keep it clean by adding Seafoam to my gas tank, a couple of times a year. I also use it on my motorcycles and my car. My wife's Silver wing had an issue with the fuel gauge sticking and we treated it with Seafoam and it corrected the problem. Same issue, gummed up from infrequent use.


Most important point the video made is you HAVE to run these things monthly. I let mine run for at least a half hour, if not normally using. Helps keep your house batteries charged,  also.
 
Before you mess with the carburater do as kdbgoat suggests. It's important to have a good fuel supply. If the coach is older, suspect a suction leak from the fuel tank to the fuel pump. Old hoses get dried out and brittle and will let air in. Not only the hose at the generator, also from the tank to the fuel line. A Mighty-Vac is a handy tool for drawing fuel up to the generator.
 
I know this isn't helpful but...  Mine ended up being either a loose plug wire, bad contacts to the 5A fuse, or just the position of the moon.  It's running perfectly now and I really didn't change anything else.  Hmmm!
 
Good information.  I had to replace my carburetor and fuel pump but now when I run the gen when driving it shuts down.  Trying to figure out what the problem could be now.  You mentioned a crack in the fuel line at the fuel tank.  Would that starve the gen and cause it to shut down?  How can I check that?  Are gens prone to vapor lock?  If so what can I do about that? 
 
Yes to both questions.  The main engine has a fuel loop sending excess fuel back to the gas tank so fuel doesn't sit in the fuel line long enough to pick up heat and vapor lock.

The generator only pulls as much fuel as it needs through it's fuel line,so the fuel sits in the line longer and absorbs more heat.

The main engine has an in-tank pump that pushes fuel out of the tank.  The generator's fuel pump is located at the end of the fuel line, so it has to suck fuel out of the top of the tank like drinking through a straw.

Any vacuum leak between the top of the fuel tank and the generator's fuel pump will suck air into the fuel line, reducing fuel flow to the engine.

You can check the hoses going in and out of an in line filter and in and out of the fuel pump pretty easily, but you'll have to drop the fuel tank to inspect the hose between the tank outlet and the start of the fuel line.

An easy way to verify a suction problem is to connect a hose to the inlet side of the fuel pump and dip the other end into a gas can.  If the generator runs OK this way you have a suction problem.

If the problem persists after this and only when it's hot, you have vapor lock.  All you can do is see if you can shield the line from heat or move it further away from hot items like the exhaust pipe.
 
GemiNiveK said:
I know this isn't helpful but...  Mine ended up being either a loose plug wire, bad contacts to the 5A fuse, or just the position of the moon.  It's running perfectly now and I really didn't change anything else.  Hmmm!
I spoke too soon.  Mine ran fine with a load for an hour a few days ago, but today it'll only run for about 30-40 seconds before it dies, and that's with zero load (gen set breakers off).  Once it dies it seems to flood because I have to wait about 10 minutes before it will start again.  Grrrr...
 
Anyone know what the pressure range should be on an Onan generator fuel pump?  I'm guessing 2-4psi...
 
 
(gen set breakers off)
If you are refering to breakers directly on the generator itself, it may not work too well that way as the Genny control circuit has to 'see' 120V being produced so that the engine will continue to run. Not sure though where that detection actually takes place..... IE before or after those breakers.

Once it dies it seems to flood

Carburetor float issue? The fuel not being cut off and overfilling the bowl perhaps?? Pump itself overrunning after the engine stops?? Your guess of 4-6 lbs. seems about right,  but it has been a looong time for this old memory.
 
Alfa38User said:
  If you are refering to breakers directly on the generator itself, it may not work too well that way as the Genny control circuit has to 'see' 120V being produced so that the engine will continue to run. Not sure though where that detection actually takes place..... IE before or after those breakers.
I get the same result with those breakers on or off.  I believe the 120V test happens before those.
 
Some notes from experience and observation:

a. Onan fuel pumps are about 3.5 psi.
b. It seems that about half the time the problem is a vacuum leak due to deteriorating fuel line. I actually had one that would run only above half tank of fuel due to this, and the mh was only five years old!
c. Overheating is often due to dust in the generator compartment. Try blowing it out. Mine would get that way afte only a few weeks of summer driving.

Ernie
 
Ernie n Tara said:
Some notes from experience and observation:

a. Onan fuel pumps are about 3.5 psi.
b. It seems that about half the time the problem is a vacuum leak due to deteriorating fuel line. I actually had one that would run only above half tank of fuel due to this, and the mh was only five years old!
c. Overheating is often due to dust in the generator compartment. Try blowing it out. Mine would get that way afte only a few weeks of summer driving.

I have about 3' of rubber fuel line but then it switches to a metal tube that runs about 6' before it disappears above the tank.  Fuel pressure is good, and I just replaced the pump in case the 15-year-old original was getting flakey.  I also replaced the rubber line between the pump and that tube.  I'm at 1/2 tank of fuel, so I will go fill up and see if that changes anything.  I'll also hit the generator compartment with my air house to get dust out.  Thanks!
 
Still no luck here.  Runs fine on starter fluid spray, getting fuel, so I think the carb is gummed up.  Put some Sea Foam in it and will let it sit for a while.  Otherwise, time to rebuild/replace carb...?
 
Quick recap:

It was having issues a week ago.  A few days ago I wiggled the plug wire and checked the 5A fuse after which it started fine and stayed running.  I turned on both the front and rear 13,500BTU air conditioners and it held the load just fine.  I drove around like that for about 30-45 minutes.  Two days later, it would start but then only run for 30-45 seconds.  Then I'd have to let it sit for a while before it would even start again.  Attempting to restart it immediately after it died resulted in rich gas smell from the exhaust.

Since then, I've done these things:
  • Checked oil levels...full.
  • Replaced the fuel pump, fuel filter and air filter.
  • Verified that the pump is pulling plenty of fuel from the tank.  Even let it pull from a gas can just to be sure.
  • Verified the pump was pushing fuel up the line.  I even let it pump into a gas can jut to be sure.
  • I checked the voltage to the fuel pump while cranking.  Was kind of clumsy to keep the contacts touching my meter, but it went up to 11.xV.  Close enough for me.
  • Removed air filter and sprayed starter fluid into intake while cranking.  Genny fires right up.  Keeps running as long as I keep feeding it ether.
  • Tried to get some Sea Foam (cleaning fluid) into the carb via the main fuel intake line.  Not sure how much made it in.
I'm going to let the Sea Foam sit over night, but I'm not at all optimistic, but for now I'm blaming a gummed up carb.

Anyone agree/disagree with my diagnosis at this point?  Thanks as always!
 
By the way, the model number of my Onan is 5BGEFA26100P.

The carb bowl has an altitude adjustment mechanism that turns up to about 90 degrees to vary the metering(?) for 0-10,000' altitude.  I can't for the life of me figure out a way to drain my bowl without pulling off the entire carb, and I really don't want to do that since I don't have gaskets, etc.  There's some pretty good information here:  http://www.generator-parts.com/onan/1GENSETS/9650231.pdf
 
After letting it sit overnight with Sea Foam in it I had to start it with starter fluid (ether) again and keep spraying in bursts until the Sea Foam cleared.  But once it was running smoothly on its own it was right back to old tricks.  :-\  It ran for maybe 20 seconds than sputtered and shut off after which it wouldn't start again.  Waited about an hour and tried again.  This time I got about 10 seconds of run time.  It's hard to believe it started and ran like a champ with a full load for over an hour just 4-5 days ago.  Since it will keep running as long as I'll feed it starter fluid, I have ruled out stuff like the governor and the low oil level sensor.  I'm still blaming the carburetor...and getting frustrated and discouraged.  :mad:
 
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