Air bubbles in fuel line
 

Hi, everyone.

I’m running into a strange fuel delivery issue. Long story short, I was draining gas out of the gas tank by connecting a hose to the fuel line (next to the brake pump) and powering the gas pump (using the check jumper).

Flow was high and steady up for two to three minutes, then flow became weak and air bubbles started showing up. It was consistent. Video here:
A few facts:
1.- Car is level to the ground
2.- Tank was ¾ full
3.- Fuel pump assembly is new (one month old) - not just fuel pump
4.- Fuel lines look fine – no leaks anywhere
5.- No kinked fuel lines inside the gas tank
6.- No bent steel fuel lines
7.- Based on sound, the fuel pump seems to be running at constant speed

Of course, this is causing a lot of different issues.

Where is the fuel pump picking up air from? What is happening here? Any ideas are welcome.

Thanks in advance!

Likely the inflow into the cup is slower than the output of the pump at zero pressure

For sure! What could be causing it?

The design of the cup...the inflow holes are small.

At 0 pressure the pump flows a lot more than the engine could ever use.

Does it do it if you stop for a few minutes and let the basket fill up?

If I let it sit for a few minutes and power the pump, I get good flow again for a minute or two, then the bubbles come back and flow goes down.

Is it possible that there is no air flowing into the tank? EVAP air filter clogged?

I think you are over worrying it :-)

Not a normal scenario and therefore not an issue ;-)

dannobre is right.

The pump is able to move much more volume when there is no pressure and the bucket is draining.

The only scenario in which this would happen while driving, is if you were wide open throttle for 3 minutes AND your engine was able to consume that amount of fuel. Which it's not.

If you think its the evap just take off the fuel cap to let in air.

Too late. I already took the tank off the car. I will test the air filter as per the FSM.

In principle, I agree with everyone's assessment that the bowl is running out of gas.. I also agree with the engine not needing as much gas as when draining the tank. However, I think the bowl is just taking too long to be refilled which could explain fuel starvation at the track with over 3/4 of a tank.

So, if you guys have any other ideas, even educated guesses, they are welcome.

without restriction from your fuel rail and injectors the fuel pump will flow to its maximum pumping ability.

The fuel pump assembly is not designed to flow that much fuel and cannot keep up with the pumps demand so it will suck the assembly dry and cause your bubbles you are seeing. Stop the pump and the assembly will fill up.

https://www.rx8club.com/series-i-maj...176491/page31/

Read from post #762 onwards. This will explain your other issues

No need to rip out your tank.

sorry, half of what you keep posting is just BS assumptions rather than proven fact i.e. gunk swelling up and blocking the sock, etc. thats a ridiculous assessment

Tank is off the car as:
1.- it is MUCH easier to work on fuel pump, etc, due to the roll cage's main loop
2.- there is other work I'm doing that requires access to the area above the tank

Now that it is off, I'll be inspecting and testing most every component.

lol your to funny Team knew you would show up to call BS on something.



Yup my own personal findings that I have experienced.




Didn't Say that.


Such a downer around here aren't you. Move along party pooper.