Fuel line test

[Piper J3]

I have 912ULS, so not familiar with 912iS engine or fuel system. I did however locate a stubborn leak in my fuel tank with use of ACDelco 1148963 Multi-Purpose Fluorescent Leak Detection Dye and a powerful UV flashlight. Worked a charm….

[BillL]

Originally Posted by Mikeyb

Fuel pump installed. Limited pressure to 30 psi but I have an AFP FI fuel pump. I found a leak in the pump!
Leak testing is an art. It’s hard to define an acceptable leak rate. You are looking for bubbles that take 10 minutes to form 2mm diameter in pure water. Using a real leak detection fluid like “Snoop” helps because it forms small bubbles faster that look like fuzz. It’s not hard to get it tight enough that the pressure remains unchanged for days and you can see the pressure rise and fall with temperature.

This is not the only pump that has leaked. I used 30 psi and have been promoting this test method for 5 yrs or so. It is really the best way to find the leaks. Pick your best detector fluid!

To the OP question about leak down overnight. It should be really small like a couple psi, if 10psi then you likely still have a leak. Always be sure to bench test the fuel pump assembly as much as practical . . . the fewer joints to test in situ is just a time saver.

Be sure to torque your 3003 tubing B-nuts not just tighten them, they can be over torqued, damage the flare, and result in a possible failure point in the future.

[UNCRV]

Originally Posted by BillL

This is not the only pump that has leaked. I used 30 psi and have been promoting this test method for 5 yrs or so. It is really the best way to find the leaks. Pick your best detector fluid!

To the OP question about leak down overnight. It should be really small like a couple psi, if 10psi then you likely still have a leak. Always be sure to bench test the fuel pump assembly as much as practical . . . the fewer joints to test in situ is just a time saver.

Be sure to torque your 3003 tubing B-nuts not just tighten them, they can be over torqued, damage the flare, and result in a possible failure point in the future.

I finally found the leak was in the cheap crappy pressure gauge after pulling my hair out. Changed the pressure gauge and magically the leak disappeared. Ended up making two new lines on the interior side of the firewall because I was afraid I damaged the flair over tightening them. After removal I looked at them with a loupe and the flair looked ok but gave me more piece of mind. I have been tightening them to 75 in/lb since that point. After this it held within 2 psi for almost two months for that section of tubing. Funny how on a car I would put all this stuff in and not think twice about any of it but when in the air and you are depending on it to not fail it makes me think very long and hard about each step. I want it to be as safe as possible for myself and family.