Fuel pump help, fuel pump pressure return Options

[porscheteck914]

Hi Fellows , I need some help /advice . 1973 914 1.7 with original Fuel Inj. Djet . Original 50 year old fuel pump -3 ports. When I go to start it , I have to bump the ignition switch 2 times to get it to start. Fuel pump runs . I have a fuel pressure gauge hooked up to drivers side fuel rail. Pressure goes to 36lbs when I turn on ign switch. When I turn off ign switch, pressure immediately drops to 0 psi. The real question is : Does the fuel system supposed to hold pressure or slowly leak down after ign switch is turned off ???? Does fuel pump have a pressure valve in its return to tank, to hold some pressure ? Do I need a new fuel pump ? thank you for any help . (IMG:style_emoticons/default/confused24.gif) Paul

[ndfrigi]

Hello @porscheteck914 ,
Looks like you have issue with ignition switch (which usually fail). Your fuel pressure with 36psi is on a high side. Usually 1.7djet should only have around 28psi. You can adjust the pressure on your fuel pressure regulator.

[brant]

For the original poster

You are correct
The 3 port original design should hold pressure when the car is shut off

I had to replace my pump when I had the same problem you are describing. Pressure would bleed to zero requiring much more cranking to start because of the lag for that pressure to rebuild


Turning the key/hearing the pump build up pressure 3x before I starting would help my car start without the excessive cranking


Changing the pump fixed it

And I tore my old pump open and saw the actual seal that was failing when I did it years ago


As mentioned 20-30 psi is the correct setting for fuel pressure
But changing your pressure back to 30 psi will not fix the bleed off problem by itself

[porscheteck914]

For the original poster

You are correct
The 3 port original design should hold pressure when the car is shut off

I had to replace my pump when I had the same problem you are describing. Pressure would bleed to zero requiring much more cranking to start because of the lag for that pressure to rebuild


Turning the key/hearing the pump build up pressure 3x before I starting would help my car start without the excessive cranking


Changing the pump fixed it

And I tore my old pump open and saw the actual seal that was failing when I did it years ago


As mentioned 20-30 psi is the correct setting for fuel pressure
But changing your pressure back to 30 psi will not fix the bleed off problem by itself

Thank you thank you ! I was kinda thinking along that line . but I dont have very much experience with the system .

[wonkipop]

the pressurized circuit after the pump and to the injectors should hold pressure.

i'd say the little rubber tip seal in the pump top port assembly is kaput.
instant bleed down.

everything you want to know about these pumps is here.
i have rebuilt mine.

http://www.914world.com/bbs2/index.php?showtopic=350416

but i do not know where you would get that little rubber tip seal that is inside the 3 port assembly at the top of the pump. fortunately that tip seal was good in the two pumps i fixed up.

i've tested mine since rebuild.
the bleed down on pressure is very slow when its like a proper functioning pump.
still holds pressure 24 hours later.
not at 28 lbs but its still got pressure.

35lbs is high.
prpbably been adjusted up the fuel pressure regulator to cope with bleed backwards at the fuel pump.

should be 28 as suggested by other posters for a D jet.