Testing fuel system

[bobm488]

I just installed my fuel tank, regulator and fuel lines. I was thinking about pressure testing the system by re-circulating a ½ gallon of gas before I start buttoning things up. I would temporally route the fuel supply line back through the fuel level opening in the tank and energize the fuel pump.
I would appreciate anyone’s thoughts.

[CraigS]

You need to block off the system somewhere or there won't be any pressure, just flow. I would pull the return hose loose at the tank and plug it. I am assuming you have an electric in-tank pump so you would be checking everything except that one connection. Two cautions; 1- since the gas cools and lubes the pump, don't let it run dry. 2- I would make up at least a 6 ft harness to power the pump. Make your pump connections first, set your battery as far from the car as you can, and connect to it last. Unless you put an actual switch in the wiring, the tiny spark made when you touch wires to battery terminals needs to be well away from the gas. Well, a final thought. Skip the gas and rig a way to pressurize the system w/ air.

[edwardb]

Obviously it's important to check the lines carefully the first time they're pressurized. I'm just trying to understand the value of doing it now versus later when everything is installed, e.g. the engine, and hooked up. First time you power up the pump you'll want to check everything over and fix immediately before proceeding any further. Then check again at your first start, and as many times as needed to fix any issues and be confident all is good. Along with every other fluid connection you have. How is that different than now? Unless you're doing something unusual or whatever. I'm assuming an in-tank fuel pump? IMO, 1/2 gallon of fuel in the tank is maybe a little marginal. I'd put a gallon or two minimum in there. You want to make sure you get good fuel pickup and also the pump is immersed as CraigS mentioned. Also let's you confirm your gas gauge is working.

Now having said the above, I personally do check lines individually when making up lines with -AN connectors, which is mainly what I've used. Don't know if that's what you have. I use this simple tester and dunk the individual hoses before assembly. https://www.summitracing.com/parts/fra-900666. Makes me feel better I guess. But in two builds where I've used it, haven't had a leaker yet. Quality parts put together properly are quite robust at the typical fuel system pressures.

[bobm488]

Thanks, I have an in tank pump, Pro-m hanger and LS Fuel Filter/Regulator. I was hoping to prove out all my connections prior to permanently attaching trunk panels. I really like finishing one project before starting another, seems almost impossible with this car. I plan on restricting the flow back into the tank to add a little back pressure.
Next up is the dreaded electrical.

[Avalanche325]

I'll go with edwardb. Just make the leak test part of your pre-first start. Nothing wrong with an early check, but a lot of effort for something that takes two minutes after everything is ready. With an electric pump it is even easier since it pressurizes the system pre-start. Make sure that all fittings will be serviceable after the car is complete. I had to snug one last week after 24,000 miles.

When you get there, I recommend:
1. Do it outside. If it goes really really wrong, you don't want your house at risk.
2. Have fire extinguishers at the ready.
3. Have a helper looking under the car for leaks when you are siting in and starting it.

[phileas_fogg]

Like you, I was nervous about my EFI fuel lines. So I bought an AN test fixture like edwardb recommends, pumped the pressure up to 100 lbs with a bicycle pump, and dunked them in a bucket of sudsy water. When you do, be sure to wiggle the fitting around at the ends of the hose under the water. When I tested my power steering hoses (they got 150 lbs) I found a couple of fittings leaked and needed to be redone.

I waited until the fuel system was complete before testing the pump. I put a couple of gallons of fuel into the tank and powered up the pump. I checked every connection, and found a couple of brass fittings needed to be tightened. Don't let the soft brass fool you; they're pretty darn robust.

I also found one AN fitting to my hard lines had just the tiniest leak by wrapping a paper towel around it and noticing the discoloration. That particular fitting required a conical seal (https://www.summitracing.com/parts/ear-169106erl) and some serious wrenching to get it to work. My thread on that issue is here: https://www.ffcars.com/forums/17-factory-five-roadsters/612626-return-fuel-line-weeping.html.

One last tip: use oil as a lubricant when mating the connectors.


John