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Discussion Starter #1 (Edited)
Hey guys! I’m not a Fj owner. But I do have a Lexus GX that I can’t seem to stop adding things to do to it. I like to follow this forum to get ideas on different mods. I read the MAF aux tank thread as I couldn't or maybe just missed it on how they plumb into the stock tank. I’m in the planning phase and bought a few pieces to get ready to install it all in one day.

Parts
• 1988/89 Ford F150 rear mounted tank 19gal
• Ford sender unit
• Ford Vapor Valve (located at the top of the tank)
• Mr. Gasket 12s Fuel Pump
• 5/16” brass tee, shut off valves and fuel line
• 1/2 “ vent line
• 30mm Radiator hose adapter
• 1/2” shut off valve

I attach a diagrams of my plans as I do wanted feedback on what will and will not work. I didn’t include the aux tank filler neck part as I undecided on where to mount as the dual filler necks a hard to come by.

Step 1:
I plan to run a 5/16” feeder line from the ford sender unit to fuel pump and than to the filler rubber stock filler neck where I will insert the radiator adapter to feed into the tank. A 5/16” valve will be installed close to the stock filler neck.

Step 2:
I plan to run a 5/16” return line from the ford sender unit to and stock vent line. A 5/16” valve will be installed close to the stock vent line.

Step 3:
I plan to run a 1/2” line from the ford vapor valve over to the Charcoal Canister’s vent line.





I think I would stay sealed this way and would have valves in place incase I have problems and with codes and have to re think things. Please feel free to give your thoughts.
 

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Good Luck, I def. want to follow your progress as I would like to add a second tank also . . .
 

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Sorry I can't be much help with your fuel tank, but I have to say, I have seen your rig on other sites and I think it is the coolest GX I have ever seen. In fact I almost purchased one to build up after seeing your build thread. :cheers:
 

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Hey guys! I’m not a Fj owner. But I do have a Lexus GX that I can’t seem to stop adding things to do to it. I like to follow this forum to get ideas on different mods. I read the MAF aux tank thread as I couldn't or maybe just missed it on how they plumb into the stock tank.
There are 2 versions of the MAF tank plumbing.
Version 1:

Stock filler pipe modified near filler opening with welded on splitter pipe to allow gas to flow into both the main tank and the Aux tank. Lower down on the stock filler pipe a threaded fitting was added and is where the output of the Aux Tank fuel pump output is plumbed. The FJ main tank vent line is plastic and runs from the top middle of the tank to the emissions plumbing behind the rear axle. MAF Tee'ed into this line to vent the Aux tank.

Version 2:

The major difference is moving the Aux tank vent. The filler pipe now has an additional modification so the Aux tank vent now Tee's into the top of the filler pipe instead of the the Main tank plastic vent line. Early versions had the transfer pump inside the Aux tank, later one have the transfer pump external to the tank but that doesn't really change the connections to the main tank plumbing.
 

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Discussion Starter #8
I hope the radiator hose will not have fuel in it (or is it a steel adaptor?)
If so it wont last to long before it swells up and disintegrates before your eyes :mecry:
No. It's a steel adapter that I wouldn't be using as I decided to drill and thread, a lone with a barb to feed directly into the filler neck on the tank.
 

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Did you ever finish this? I'm thinking about doing this mod down the road, and am definitely watching what you're doing. Maybe you could add some captions to explain a little better what the pictures are exactly showing.
 
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