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Old 04-06-2016, 06:26 PM   #1
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Booster fuel pump between gas tank and generator

I have been working with a couple shops to resolve code 36 on my Onan generator (shutting off for no reason). This first shop (certified Onan) put in a booster fuel pump halfway between the gas tank and the generator. That stopped the generator from quitting, but the booster fuel pump was working so hard that it was unbearably loud. So loud that it made the rig unusable as we had to speak loud over it.

Then took it to Rocky Mountain Cummins in Phoenix to see what they could do. The FIRST thing they did was bypass the booster fuel pump. After testing, they determined that the original fuel pump (not booster) needed replacing. They are in the process of changing that out now.

Has anyone ever heard of adding a booster fuel pump between the gas tank and the generator? The first shop is telling me that it is very common to add boosters especially on longer rigs. Rocky Mountain disagreed saying it is uncommon, but not unheard of. Not finding much online about a booster fuel pump for Onan.

Thoughts?
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Old 04-06-2016, 06:40 PM   #2
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It is uncommon to add a booster. It is much more common to have an onan fuel pump take a dump. I went through 3 plus the original before I finally had one that lasted. I carry a spare at all times.
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Old 04-06-2016, 07:59 PM   #3
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Maybe the first guy (Onan certified) was/is on to something. If Onan fuel pumps are failing at a higher than normal rate, especially on larger rigs, maybe a booster does help by not making the main fuel pump work so hard at pulling gas from a tank 25 to 30 feet away. My gas tank is in the rear and my geni is in the front. My understanding is that a fuel pump will fail sooner if forced to work at max or more most of the time. If a booster is added, both pumps would work more efficiently, thus last longer?
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Old 04-06-2016, 08:51 PM   #4
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I have heard of adding a booster pump, and thought of doing it my self when I was having issues. I can see it helping in long fuel line runs but I would use just the onan for a while and see how it goes. Check with others that have your rig and see if they are having similar issues.
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Old 04-06-2016, 09:03 PM   #5
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Depends on pump.

If old school selenoid plunger type with a diaphragm they can have multiple problems not pump related.

First is listen to see if they pump up correctly and stop.

A pin hole in the supply line will cause more running as it is drawing in air.

If the pressure is low cleaning check valves.
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Old 04-06-2016, 10:01 PM   #6
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Every one of the pumps I had fail, failed quickly. The first one went out in the first 3 hours so I dont think its a matter of them being overworked, I think it is a component in the pump that is failing due to bad design, improper manufacturing / assembly or a part not up to specifications.
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Old 04-07-2016, 04:06 AM   #7
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A booster pump on a diesel, yes, because of the distance of the draw. On a gas coach no, it's located in the rear near the gas tank.
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Old 04-07-2016, 06:52 AM   #8
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My generator is in the front, gas tank in the back
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Old 04-07-2016, 07:21 AM   #9
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Even diesel pushers, with the long distance from tank to genset, rarely need boosters. It's not an uphill pull, so the pump load isn't that great. Not really any different than pumping fuel to a gas engine motorhome, where the fuel tank is in the back and engine in the front.

If the main pump is weak, or if the fuel line has pinholes, cracks or is pinched, a booster will help. And maybe is cheaper than replacing the line. However, a bad fuel line or pump is only going to get worse and eventually you need to bite the bullet if that's the problem.


The smaller Onan gas gensets seem to need fuel pumps more often than the larger models or the diesel gensets. Maybe a poor pump design on those?
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Old 04-07-2016, 07:50 AM   #10
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In 2013, I bought a new Onan 4K generator rather than pay almost as much to repair the 14 year old original. We then left for a cross country trip and the nice new generator wouldn't keep running while driving (it ran fine when stationary). A technician at the Cummins Onan repair facility in Sacramento recommended adding an auxiliary fuel pump and the genny has performed correctly ever since.

I had previously done the usual fix of replacing the fuel line and, on a short 29 Ft. class A, it doesn't seem like an auxiliary pump should even be needed, but it absolutely solved the problem. I bought a small pump at an auto parts store, mounted it near the gas tank, and can only hear it when nothing else is running. The newer Onans don't have a 12V supply when running so I wired the pump to the coach 12v system and use a (lighted) switch to turn on the fuel pump.

Quote:
Originally Posted by raineman View Post
...Has anyone ever heard of adding a booster fuel pump between the gas tank and the generator? The first shop is telling me that it is very common to add boosters especially on longer rigs. Rocky Mountain disagreed saying it is uncommon, but not unheard of. Not finding much online about a booster fuel pump for Onan.

Thoughts?
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Old 04-07-2016, 08:30 AM   #11
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Quote:
Originally Posted by George Schweikle View Post
In 2013, I bought a new Onan 4K generator rather than pay almost as much to repair the 14 year old original. We then left for a cross country trip and the nice new generator wouldn't keep running while driving (it ran fine when stationary). A technician at the Cummins Onan repair facility in Sacramento recommended adding an auxiliary fuel pump and the genny has performed correctly ever since.

I had previously done the usual fix of replacing the fuel line and, on a short 29 Ft. class A, it doesn't seem like an auxiliary pump should even be needed, but it absolutely solved the problem. I bought a small pump at an auto parts store, mounted it near the gas tank, and can only hear it when nothing else is running. The newer Onans don't have a 12V supply when running so I wired the pump to the coach 12v system and use a (lighted) switch to turn on the fuel pump.
Connect a 12 volt power supply or 120 vac relay to the generator power line generator side of ats.

Generator should start without booster or add a push button to manually prime it.

Then it is automatic as generator running is powering pump.

Turn genny off and pump goes off.
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Old 04-07-2016, 08:57 AM   #12
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When I was seeing a lot of pump failures on the Onan generator, I finally tore down a couple of the vane pumps and found rust had jammed the vanes in the pump. The rust was like very tiny pieces of sand. (except they were magnetic.) I checked with the Onan installation manual and it called for a filter before the pump. I started installing a filter before the pump and never had a pump failure on a generator that had a filter before the pump.
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Old 04-07-2016, 08:59 AM   #13
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Wonder if running a vacuum test on the fuel line at. Just before fuel pump. See if the Gens pump is just not able to keep up with fuel delivery because of size or routing of fuel line.
Also diesel pushers fuel is normally very close to the Gen as the rear is motor and transmission, fuel is just behind front tires.

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Old 04-07-2016, 06:39 PM   #14
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Quote:
Originally Posted by Bruce C View Post
A booster pump on a diesel, yes, because of the distance of the draw. On a gas coach no, it's located in the rear near the gas tank.
my gasser has the gen up front under the couch, probably 25' away from gas tank
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