Aux Tank: troubleshooting intermittent fuel flow

Joined
Nov 4, 2010
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80
Location
Atlanta, GA
I have an FJ40 with a newly installed man-a-fre aux tank set up as a second primary (OEM mechanical fuel pump). Fuel has been flowing fine since install but recently, the FJ has been choking down randomly after I switch to the aux. Front tank works fine so I’ve started working my way back from the relay to id the issue. Installed new relay, new filter, blew out the line…still choking down every few miles when I switch to aux from front tank. About to check the aux breather valve and relay switch (in dash). I noticed the switch in the dash has 5 wires (2 red, a blue, a green, a yellow w/red stripe) connected to a 6-point relay. I don’t see a missing wire that has come unplugged - could this be my issue or is there a situation where that set up (pics attached) can be fully functional?

Any thoughts greatly appreciated.

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Joined
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Cherry Valley, NY
Throw an electric fuel pump on a dash switch in the aux tank line. I used to have to crank, crank, crank mine until I had fuel preasure, now I just hit the switch for a few clicks of the electric pump and BAM!, fuel.
 
Joined
Nov 4, 2010
Messages
80
Location
Atlanta, GA
Thx, Paul. Mine has pressure but loses flow midstream randomly. That could definitely help but don’t think it’s my primary issue. My guesses are I either have a short in my switch, or I’m missing a wire for that 6th terminal, or it’s a vapor lock issue.
 
Joined
Nov 4, 2010
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80
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Atlanta, GA
Update, think I have something in the tank (gasket material?) stopping up the line in the tank. Guess I will need to remove and clean out the tank unless anyone has found an easier way to do that…

As always, advice welcome.

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Joined
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Idaho Falls, Idaho USA
On my recent FJ40 overhaul and return to service, I had to drain, rinse, and flush the first tank 3 times to get it totally clean. It has a approx. 30-35 gal aux tank in the rear, between the frame rails, and I didn't even attempt that one. Trying to talk my son into removing that, and running proper dual exhausts for the 289 V-8 in the huge void space. Is there a market for the used aux tank???
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Joined
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moncton., nb. canada
i had a similar problem., when i changed the fuel hoses, i didn't blew air before hooking.....guess what.. it force me to do something i had long waited for....carb kit....thanks to this forum i was able to do a carb job and learn from my mistakes. good luck to you
 
Joined
Jan 17, 2005
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6,259
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Southern Colorado
On my aux. tank, the switching valve was leaking air, randomly, into the fuel stream.

I only discovered this when I converted the truck to EFI and installed a clear plastic fuel filter and saw massive bubbles on the inlet to the electric fuel pump. I was so annoyed that I just yanked the aux. tank. I fought aux-tank battles for too long to want to mess with it any more.
 
Joined
Nov 4, 2010
Messages
80
Location
Atlanta, GA
On my aux. tank, the switching valve was leaking air, randomly, into the fuel stream.

I only discovered this when I converted the truck to EFI and installed a clear plastic fuel filter and saw massive bubbles on the inlet to the electric fuel pump. I was so annoyed that I just yanked the aux. tank. I fought aux-tank battles for too long to want to mess with it any more.
Fair, Steve! Can’t say the thought hasn’t crossed my mind!
 

65swb45

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Last edited:

Spike Strip

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Yup. :mad:
 

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