Fuel pump options, Staying in its original location Options

[emerygt350]

I am having a very specific issue here. Pump no longer holds pressure after shutdown. Original location, original three port pump. It still pumps great when running, but no longer holds pressure. Need to fix that and quick. Do I have to replace it or can it be repaired?

[wonkipop]

@emerygt350

i was watching the full unedited version of the interview with the mclaren mp4/4 F1 car designers last night on youtube before going to bed.

towards the end there was a new added section.
a discussion about the fuel system.

it seemed the mp4/4 suffered from fuel vaporisation problems late in races due to the circuit the fuel ran in, which meant it had to be drawn up from the bottom of the tank bladder and over the engine and to the rear of the engine. this also increased the temp of the fuel in the total circuit. sometimes the fuel in the tank would start boiling.
and the car would suffer starvation as the main pump began to cavitate.

the solution was pretty good. they built a little catch tank of sorts under the quick fill fuel cap and pumped first to it and pressurised at a low pressure of 0.5 bar. this was enough to keep the fuel feed to the main pump liquid. they made a check valve themselves out of a ball bearing and the spring from a ball point pen. (IMG:style_emoticons/default/biggrin.gif)

the pressure was quite low. 0.5 bar = 7 lbs. it was done with tiny electric fuel pump.
way less than the pressure in a 914 injector circuit or an F1 turbo engine.

the comment was made in the video by the engineers that pumps only like to pump and not suck fuel. a good flow is required for feed. a good flow can be simulated by a small amount of low pressure. so the main fuel pump which generated much higher injector pressure was fed by this low pressure line. the tank itself and return circuit remained unpressurised.

one way around the old 914 problem is not necessarily to go the high pressure route from the tank to the engine as per 75 cars but simply to induce a small amount of pressure in the feed line from the tank with a tiny pump?

i dunno? just a thought. it may be enough to keep the fuel from boiling in the critical part of the fuel line after the tunnel and before the fuel pump. a low pressure feed.

https://www.ebay.ie/itm/293759097396

such pumps are very small. easily accommodated discretely under the tank.
and with less stress on the fuel lines through the cabin if you don't have the steel lines in yet. or you don't feel comfortable with a higher pressurized line through the cabin (which i must admit is how i feel re high pressure line through the cabin - i know that is probably not rational given i have steel lines in now......but).