Fuel tank sump 1/2 tank issues

thatguy69

thatguy69

New member
So I installed a sump on my friends truck along with a fass 150. Anytime his tank is below 1/2 the sump starts sucking air when coming to a stop sign etc. I installed the same exact sump on my truck and I don't have this issue until I get down under 1/4 tank. The only differance is his truck is shorted and mine is long so I think my tanks bigger than his. What am I missing?
 
If it's 2nd gens both, I'd question the fuel gauge accuracy between the 2. Mine were always just suggestive
 
Did you locate sump under fuel sending unit? also questioning level but I had one come in that on wot take offs with 1/4 tank the truck would get air because they installed sump way to far forward.
 
fire power said:
Did you locate sump under fuel sending unit? also questioning level but I had one come in that on wot take offs with 1/4 tank the truck would get air because they installed sump way to far forward.
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I put it on the flattest spot of the tank which was just a little past halfway towards the back on his. on mine I put it more towards the front but I had a hard time getting it to seal because of the bow in the tank. I had to redo mine with rtv so it would seal.
 
thatguy69 said:
I put it on the flattest spot of the tank which was just a little past halfway towards the back on his. on mine I put it more towards the front but I had a hard time getting it to seal because of the bow in the tank. I had to redo mine with rtv so it would seal.
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If your in the center you are still forward of the sending unit which is where your return fuel comes back in. But my guess is your sender went bad or you got some other problem
 
Additional related question- what's the best sealant to use to ensure no leaks with bottom of tank style sump?
 
RacinDuallie said:
Additional related question- what's the best sealant to use to ensure no leaks with bottom of tank style sump?
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I have used right stuff in the past but if you use the newer style double oring kind you shouldn't need any sealer or least o have never had the oring style leak

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I can’t believe that at a half tank the fuel could even move far enough forward to starve the sump. Tell him he doesn’t have to pull the chute at every stop sign. My truck use to run out at a 1/4 tank when I did the 1/2” draw tube mod. I switched to a Hellman sump and I could drain it after that. How is the return for the fass setup? In the filler neck?
 
smoken02 said:
I can’t believe that at a half tank the fuel could even move far enough forward to starve the sump. Tell him he doesn’t have to pull the chute at every stop sign. My truck use to run out at a 1/4 tank when I did the 1/2” draw tube mod. I switched to a Hellman sump and I could drain it after that. How is the return for the fass setup? In the filler neck?
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I noticed it when test driving it directly after putting the sump on, and I wasn't stopping abruptly at all. Yes return is going back into the filler neck
 
smoken02 said:
I can’t believe that at a half tank the fuel could even move far enough forward to starve the sump. Tell him he doesn’t have to pull the chute at every stop sign. My truck use to run out at a 1/4 tank when I did the 1/2” draw tube mod. I switched to a Hellman sump and I could drain it after that. How is the return for the fass setup? In the filler neck?
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I should also mention I'm running factory return lines, his truck that sucks air on 1/2 tank is on the filler neck return. It's a differance I didn't mention eariler
 
You can park the truck nose down on a hill with a half tank. Crack the line loose on the sump and see if fuel starts leaking out. That would rule out the sump starving for fuel. I’d be ruling that out first. Does he have a fuel pressure gauge? Warning light on the fass?
 
Warning light on edge juice and it's accurate because it came off my truck, atleast it was accurate when pulled
 
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