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Fuel feed for built in generators

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I don't have a generator. Over the years, I've read here and elsewhere that the generator feed is designed to leave at least a 1/4 tank so you can drive home. If this is true, how do they work this magic? It's often implied that there's an outlet from the tank 1/4 of the way from the bottom. Also over the years there have been many buying new tanks and the recommendation has always been "Buy a standard Pickup tank"'. I've never heard anyone come back and complain that there's no connection for the generator. Is it a coincidence that generator owners have never replaced a tank? I've also read from time to time that the generator gets fuel from a 'T' in the engine fuel line but that wouldn't stop you from emptying the tank with the generator.

So, who's got a generator and how is it plumbed? :)

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Onan sells a tank supply fitting that goes into the tank, any tank so it's something that only draws to a certain level then runs out of gas (generator not the tank). "T"ing it into a FI engine would produce an almost immediate disaster!

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 I had a generator - been a while, but as I recall, there was a separate fuel line for the generator.  Also it had it's own electric pump. I saved it so I can pump gas from my tank if I need to.

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Of the not officially approved, but worked fine for years method. The EFI Toys have 2 fuel lines. One is a return line for excess fuel. It is part of the sender unit, it ends about 2" above the bottom of the tank.

What was done on my Toy was to T in to the return line for the generator feed. When you parked the generator sucks fuel out and will leave you with a couple of gallons for the engine after the generator quits because it ran out of fuel.

When the truck engine is running there is minimal fuel pressure on the line and the generator runs just fine on the excess fuel. of course there is no reserve fuel and the truck engine and generator quit at the same time.

MAJOR BAD JUJU IF YOU TAP INTO THE PRESSURE FUEL LINE

On an older carbed Toy you are on your own. Maybe install a EFI sender and use the return line just for the generator.

 

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I'm pretty sure the fuel returns to maybe 2" max below the top of the tank otherwise the weight of the fuel would affect the line pressure in any thing with EFI. 

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I suppose their are several different plumbing technics for this.   I really want to find out for sure. In my 1991 Toyota dolphin

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Just about everything I have ever seen dumps right at the top. Like I say it takes pressure to force fuel below the top of the level.  Correct fuel injection pressure is very important a couple of PSI makes a big difference. Onan sells kits just for that purpose that tap into the tank at any level you feel is right.

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Here's the fuel pump assembly for a 86-95.  Notice 2 fuel lines, the one pointing straight down is where the in-tank pump hooks up, the long one that points sideways is the fuel return line.

https://www.am-autoparts.com/Toyota/Pickup/fuel-sending-unit/AM-3123667870/1046538.html?gclid=EAIaIQobChMI-oDwkLi43gIVj0oNCh2q_gWjEAQYBCABEgLHPfD_BwE

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If that is the case I still would not use it what come back is still at 35 psi granted it dumping  into the tank so the pressure is only as great as the resistance but there is still enough pressure to cause an issue if there is a problem particularly if it is deadheaded, will both run at the same time? Maybe. Personally I am hesitant to tinker with anything factory they have a great deal more knowledge than I do and better engineers. Like I say Onan makes a kit just for this purpose that is their expertise.

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OK go for it.

99% of modern efi systems dump the return fuel in this fashion to prevent fuel foaming when the tank level is low. The fuel pressure regulator on a 22re is AFTER the injectors so they run at the required PSI. The out put of the regulator is 0 psi.

Tapped into the return line my Onan ran just fine for 15 years, no flooding with the Toyota engine running, parked the genset ran just fine, going across the NV desert in the summer the genset and Toyota ran just fine running the RV and the AC.

  Onans have a electric fuel pump and that helps control the pressure when the ONAN engine is running.

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Many years ago I had a BMW in the shop it did not run I checked the fuel pressure it was excessive because it had nowhere to go the return line at the rear of the car had a smashed return fuel line where he had run over something. Yes it is a what if and a odd issue but--.

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If u use a honda or mikuni low GPM vaccum fuel pump for the generator it will work perfect for a carburated  generator and never cause crazy fuel dump problems. They cost 10-20.00 ea and are avalabile at any small engine parts place. Golf cart parts  ect. This does not solve the pickup problem.  And u have to add a nipple to the generators intake manifold to connect the vaccum line to the pump.  But makes for problem free fuel pump for the genny.   

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On 11/17/2018 at 10:30 AM, Miharriblz said:

If u use a honda or mikuni low GPM vaccum fuel pump for the generator it will work perfect for a carburated  generator and never cause crazy fuel dump problems. They cost 10-20.00 ea and are avalabile at any small engine parts place. Golf cart parts  ect. This does not solve the pickup problem.  And u have to add a nipple to the generators intake manifold to connect the vaccum line to the pump.  But makes for problem free fuel pump for the genny.   

It does but be careful the generator working hard will have little vacuum because the throttle is wide open.

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I just wanted to add to this. for I've been deep in my Generator and getting it pulled out. My Dolphin came with the Onan Genset 3k with the line tapped into the gas tank and I can tell you its at the bottom. I too would have thought they would have mounted it up on the side so you cant run your tank dry but you can. I also kept my fuel line in the box where the generator was I added a petcock to the line. gas will flow most times when above 1/3 tank due to pressure. I figure if I ever get a little Honda I could use the hose and petcock to just add some gas if needed.

Edited by 86Dolphino

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3 hours ago, 86Dolphino said:

I just wanted to add to this. for I've been deep in my Generator and getting it pulled out. My Dolphin came with the Onan Genset 3k with the line tapped into the gas tank and I can tell you its at the bottom. I too would have thought they would have mounted it up on the side so you cant run your tank dry but you can. I also kept my fuel line in the box where the generator was I added a petcock to the line. gas will flow most times when above 1/3 tank due to pressure. I figure if I ever get a little Honda I could use the hose and petcock to just add some gas if needed.

On my old Escaper they tapped into the tank at the 1/4 mark! On my current rig it's in the fuel pump. 

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Yea my 86 was tapped at the bottom like wtf🤔

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My 92 Horizon taps into the efi fuel return. Works fine but will push a little fuel out causing a fuel stink, necessitating a shut off in the fuel line.  I would like to find a remote fuel shut off so I don't have to reach under the camper to turn it on and off. 

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18 hours ago, Utah-Clay said:

My 92 Horizon taps into the efi fuel return. Works fine but will push a little fuel out causing a fuel stink, necessitating a shut off in the fuel line.  I would like to find a remote fuel shut off so I don't have to reach under the camper to turn it on and off. 

Buy the tank tap from Onan it usually is about 1/4 tank high. I'm 100% against EFI tapped fuel supply especially when under power the pressure is too high for a pump that runs 3 PSI max. When the fuel tank is full the return pressure will climb, a good 50% from the EFI fuel is returned to the tank so restrictions and fuel level play a role in the return pressure. From Onan "Some vehicle manufacturers permit tying into the fuel return line on high pressure fuel systems. Contact the vehicle manufacturer for details and approval. The fuel return line pressure at the point of connection must not exceed 1-112 psi, or carburetor flooding could result" The only way would be to "T" into the system return line, because it is low in the tank on some systems it will affect the fuel return pressure very possibly exceeding the Onan spects depending on the amount of fuel in the tank.

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Funny (to me at least) is that after years of reading thousands of posts, none regarding buying a new gas tank that i can remember mentioned anything about an onboard generator hookup.

 

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4 hours ago, Maineah said:

Buy the tank tap from Onan it usually is about 1/4 tank high. I'm 100% against EFI tapped fuel supply especially when under power the pressure is too high for a pump that runs 3 PSI max. When the fuel tank is full the return pressure will climb, a good 50% from the EFI fuel is returned to the tank so restrictions and fuel level play a role in the return pressure. From Onan "Some vehicle manufacturers permit tying into the fuel return line on high pressure fuel systems. Contact the vehicle manufacturer for details and approval. The fuel return line pressure at the point of connection must not exceed 1-112 psi, or carburetor flooding could result" The only way would be to "T" into the system return line, because it is low in the tank on some systems it will affect the fuel return pressure very possibly exceeding the Onan spects depending on the amount of fuel in the tank.

I have looked for that Onan kit online but have failed in my efforts. I would prefer not to have to open and close the valve each time I used it.

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4 hours ago, Utah-Clay said:

I have looked for that Onan kit online but have failed in my efforts. I would prefer not to have to open and close the valve each time I used it.

Call Onan customer service and ask. 

Linda S

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