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Onan generator stalling


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Hi all, we have an Onan QD 7500 in our 2003 Monaco Windsor, and sometimes it has a problem with stalling.  It will run for many minutes (sometimes 5, sometimes two hours), and then will hesitate, surge, and die.  The code is a 36 (Engine stopped without command from controller).  After giving it a good long prime and an extended cranking time, it will start up again and may run for five more minutes, maybe two more hours.

So I'm assuming this is air in the fuel (though I haven't noticed any white smoke).  But I've visually inspected the fuel lines and clamps at the ends, and they look good (also confirmed by a reputable shop who had time to take a quick look, but not enough to do a deeper debugging due to my other repairs).  Nothing obviously wrong.

Now the strange thing: we just did a rally where we were boondocking, and with a full fuel tank the generator was running  great, stalled maybe once in two weeks.  When approaching a half tank (another time), it will typically run about 30 minutes (plus or minus) before stalling.  Another time when the fuel was approaching a quarter tank, it was stalling every five minutes.

I'm thinking (guessing?) there's something bad with the fuel pickup tube.  Maybe cracked or rusted or pinholes?  I haven't pulled it out yet, but psyching myself up for it.

So, does my logic make sense?  Has anyone had a similar problem or had a fuel pickup tube fail in a similar way?  And is the fuel pickup tube easy to remove?  

thanks for any advice you can provide before I tackle this,

Jason.

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Jason, going from memory here, but seems I remember Fred White having a problem with a small leak in the fuel line on his Windsor generator. I think it was on the generator itself. Seems it was sucking air. Maybe someone on the forum will recall or you can do a search. That’s all I’ve got.

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Jason,  a couple thoughts.   First, since it runs fine with a full tank, and as fuel is used, the problem worsens, I wonder if it might be a fuel pump wearing out?  Maybe the "head pressure" of a full tank allow the pump to make sufficient pressure, but as fuel is used, it can't provide the requisite pressure.   Second,  maybe if you connected a separate,  external fuel tank directly to the generator, you could eliminate fuel line problems. 

Good luck

  -Rick N.

2005 Exec, DD Series 60

20q4 JGC Overland Diesel 

Currently in Casa Grande,  AZ

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Jason, I sent this yesterday but I see it never got posted, so here it is again.

Jason, yes it sounds like your fuel pick up tube might be the problem. It also sounds like the lines or the electric fuel pump on your generator might be the problem. I assume you have changed the filter recently. The new filter could still be the problem but just keep that in mind while you check the fuel delivery lines.

 
On my coach the pick up tube can be removed but it is tricky due to its length. I have to stick the top of the tube into the slide gear space above it and then it is just enough headroom to remove it. Your mileage may vary.
 
I would start with checking the pick up tube, pressurize it somehow to check it, then do the same with the pick up tubing you removed from the metal pick up tube, pressurizing it toward the generator. If nothing shows up with the pick up tube or tubing, try a new filter before you decide the problem might be with your fuel pump. The fuel pump can be checked, but it will take some special apparatus.
 
All that said, the problem could still be elsewhere but this will help eliminate the cheap fixes.
 
-Jamie
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 Good morning Jason ,

 Like Alan mentioned I remember when Fred White had that pin hole in his gen fuel line .

 That might be where I would start since replacing the fuel line shouldn't be terribly difficult .

 Another place that you could check is the fittings at the fuel filter its self especially if this

problem followed a filter change since you are probably sucking air somewhere .

I also agree sticking a fuel line into a 5 gal container and see if it runs would be a simple test .

I don't remember ever hearing about a hole in the pickup tube , could be though .

Edited by Ray Davis
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Jason

I had a fuel line leak on our 10K generator. I replaced it and  the fuel filter on the generator with a Garber fuel filter,  as used on the Aquahot. Mounted it on the rear panel, outside, so it was much easier to service. NAPA made up all new fuel lines at that time. Worked great and simplified the fuel filter change on the generator.

Paul A

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