Testing Fuel Line Integrity
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Senior User
Joined: Oct 2010
Posts: 407
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From: Mobile, AL
Testing Fuel Line Integrity
So, finishing up my hutch mod and want to test the fittings before mounting the tank. I'm thinking I can attach the pickup hose and leave the return off, put a little fuel back into the tank and with KOEO prime the system. It should prime/ pressurize to the fuel bowl but not return to the tank because the engine isn't running. That would tell me if the mod is good before I remount the tank. I have a pressure gauge so I'll know when it has achieved normal psi.
Is that correct or am I missing something about the system? One reason I want to check the pick up is because I was thinking I should be able to blow into the pickup tube and tell if air was coming out the tank end. Well, I tried that and it was pretty tough. Now granted, that is a 3/8" tube so it would take some force to get air through it, but I really expected to be able to tell if it was clear. It certainly felt blocked when I forcefully blew into the tube. Looking for some weed eater cord or similar to snake into the pickup tube to check that way as well, but thought I'd see if someone had any thoughts about the pressurization idea. Besides, it will help me understand the fuel system a little better.
Is that correct or am I missing something about the system? One reason I want to check the pick up is because I was thinking I should be able to blow into the pickup tube and tell if air was coming out the tank end. Well, I tried that and it was pretty tough. Now granted, that is a 3/8" tube so it would take some force to get air through it, but I really expected to be able to tell if it was clear. It certainly felt blocked when I forcefully blew into the tube. Looking for some weed eater cord or similar to snake into the pickup tube to check that way as well, but thought I'd see if someone had any thoughts about the pressurization idea. Besides, it will help me understand the fuel system a little better.
Lead Driver
Joined: Jun 2004
Posts: 6,340
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From: Amarillo, TEXAS!
If the fuel pump is running, fuel will return to the tank whether the engine is running or not. The fuel pressure regulator is on the side of the filter housing, and is also the exit path for fuel to return to the tank. Not saying you can't do what you're planning to do, just be aware that fuel will come out of the return line once the filter housing is full.
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Senior User
Joined: Oct 2010
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From: Mobile, AL
And... That makes complete sense. Otherwise the pump would have to sense pressure and cycle itself to regulate that pressure. So yup, the fuel bowl uses the fuel pressure regulator (wonder why it's called that?) to return fuel to the tank when the pump is running.
Thanks for the sanity check.
Thanks for the sanity check.
Hotshot
Joined: Jan 2011
Posts: 18,849
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From: Puget Sound
Before installing my tank, I vacuum-tested all the hardware going into the tank. Vacuum likes to leak, and the pickup is under vacuum with normal use, so I figured this was the appropriate test. I never had a problem withe the in-tank mods, but I sure made a mess of things once the fuel left the tank. Double-clamp (fuel injector hose clamps) the hose at the pick-up, and it can't hurt to vacuum test from the pump inlet to the pickup before installing the pickup hardware in the tank.
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Senior User
Joined: Oct 2010
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From: Mobile, AL
I finished it up tonight and nothing leaked. But like you, CarterKraft, I have those same bubbles in the Racor. I've used the gasolia on the threads and bards, double clamped, injection clamps, etc. No obvious signs of leaks... but i'm wondering if it is even an issue to snipe hunt. I'll run it awhile and see what I think.
Elder User
Joined: Sep 2011
Posts: 979
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From: Vancouver
All fuel, especially diesel has air entrained or dissolved. Racor, Fass and other filter manufacturers have solutions for this. Basically involves an orifice off the top of filter housing and piped into a tee in the return line.
Now that I think about it, the housing would have to be on the pressure side of the pump, otherwise, the pressure in the return line would prevent the air bubbles from being deposited in the return line.
Now that I think about it, the housing would have to be on the pressure side of the pump, otherwise, the pressure in the return line would prevent the air bubbles from being deposited in the return line.
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