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Old 07-12-2011, 05:38 PM   #1
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Onan question

When I disconnect the fuel line (supply-side) from the fuel pump, there is no diesel in that line. When I disconnect the return side, diesel runs out immediately. Don't sound right to me.

BTW: the danged fuel pump is mounted in such a manner that you have to raise the generator off the rack to take the pump out! What a PITA!
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Old 07-13-2011, 07:08 AM   #2
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Does the generator run ok? If so, don't sweat the small stuff.
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Old 07-13-2011, 07:30 AM   #3
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You have a feed and a return line on diesel engines
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Old 07-13-2011, 12:29 PM   #4
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Trying to wrap my head around the problem. I think I have made a mountain from an ant hill! The return line is visibly deteriorated. No sign of fuel leakage, but it is crunched up fairly bad. Engine will start and run with fuel supply line pulling from a container of diesel within 3' of the fuel pump. Hook it back up to the line going to the RV tank and it will not run at all (well it ran for maybe a minute, roughly before shutting down). The supply line is not visibly damaged as best I can see. Can a damaged return line somehow allow air to get into the system?

How the heck does one figure out which lines are which (engine supply/return, generator supply/return, etc) on the top of the fuel tank. Hard enough to even see the lines through the fuel door. Beginning to wonder if the tank has to be dropped down to replace lines!!!

Appreciate any advise. Thanks.
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Old 07-13-2011, 12:37 PM   #5
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It doesn't sound like anything is wrong with your fuel pump, but I suspect you have a plugged supply line from the tank to the pump. I assume you have more than 1/4 tank of fuel.
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Old 07-13-2011, 05:25 PM   #6
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Dang! Never thought of that! Duh!

I can pressurize the supply line back into the fuel tank and see if that is the problem. If I hear a ka-whump inside the main tank.....

I know I need to replace the return side (it's OEM, 1998, and shows some crunched areas).

Thank you for the advise. The problem actually started immediately after a fill-up from less than half a tank indicated (probably about 50-gal on board, 130 gal tank). I assumed that the gen had sucked up some bubbles from the fueling process but it very well could have sucked up some basic-sludge-and-waste kicked up off the bottom of the tank. I did get it running a few times for a couple of hours here and there, but it just didn't "sound right". We were on a trip across Texas and it was HOT so I tried everything I knew (replaced all filters, prayed, kicked trees, swung dead cats into grave yards at midnight) but nothing worked.
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Old 07-14-2011, 10:16 PM   #7
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More than likely it is an air leak in the supply line, i.e. a deteriorated fuel hose. The pump is sucking air as well as fuel when running, and fuel drains back into the tank when it is shut down.
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Old 07-17-2011, 10:22 AM   #8
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Quote:
Originally Posted by Gary RVRoamer View Post
More than likely it is an air leak in the supply line, i.e. a deteriorated fuel hose. The pump is sucking air as well as fuel when running, and fuel drains back into the tank when it is shut down.
Gary, until I read your well thought out advise here, I was ready to award the Grand PooBah Problem Solving Award to RJay. Now, I have to wait and see how my "repair" works through a few run/stop cycles.

So here's what I did: disconnected the supply line at the generator's fuel pump and blew it out with a low pressure air hose. I could hear the burps inside the fuel tank. Then I did the same with the return line. Next, I took a small vacuum pump and pulled diesel toward the generator to fill the lines (both). Re-connected the supply and return lines, turned off the output breaker on the gen set and held down the prime button for about 90-seconds. Hit start and she cranked over for about 10-seconds (just enough time to start heart palpitations for me) and then fired up. First time since this whole debacle began (6/1/2011) that she has "sounded right". Operated under moderate load (one AC unit and fridge) for 40-minutes and she purred along perfectly.

Gonna let it stay idle for a few hours and test out Gary's theory. Gary, no offense but I sure hope you are wrong. If I had not used the vacuum pump, I may have known the outcome already.
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Old 07-23-2011, 08:00 PM   #9
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Quote:
Originally Posted by RJay View Post
It doesn't sound like anything is wrong with your fuel pump, but I suspect you have a plugged supply line from the tank to the pump. I assume you have more than 1/4 tank of fuel.
And the winner of this year's "Saved My Butt Award" goes to....drumroll...
RJay! Thanks to your input,I turned my mountain back into a mole hill and hope to live happily ever after, etc etc.

Have put 8-hours on the gen set over the past week and she has not sputtered after the fuel line blow out. I did make it a point not to start the generator for several minutes after adding fuel.
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