When the engine is turned off, the fuel pressure drops to zero within 2 hours (according to the pressure gauge.) It used to stay up for days. If the car sits for a while with out starting up, I have to prime the fuel system to get pressure. Which component would cause it to lose pressure and how do I fix this? ('77 fuel injected z) Ron

Fuel pump check vavle can cause that. It's the valve on the fuel pump that will only allow fuel to flow in one direction. Also, leaking injector(s) or any other fuel leak but you would probably notice driveability problems and/or fuel smell. Part no. 17014-N4225 Not sure if they're still available. When I needed one for my 810 I went to the junkyard.

WWW.nissanparts.cc shows it is still available

http://www.nissanparts.cc/cart/?pn=17014-N4225+&submit.x=16&submit.y=1

I've done a lot of business with them. Unless it says 'currently in stock' that just shows that it's a good part number. To find out whether or not it's available you'd have to contact them.

You could also install a inline check valve, I use them for 2000 psi hydraulics all the time. Think that is what I'll do for my Z has the same issue , injectors are good.

So why must it hold pressure once the engine is shutoff? just asking.

So why must it hold pressure once the engine is shutoff? just asking.

So that it will be primed for the next start. If you've ever run a mid 70s early 80s Datsun EFI car out of gas, especially the ones that don't start the fuel pump until the engine is cranking and has enough oil pressure, it takes a while to get them started.

Two things here I just wanted to mention for the Zsters.

My fuel pressure drops off immediately after turning off the engine, however never fails to fire right up. Just in case I have located a Kepner inline check that I plan to try.

The second issue I had was much worse my car would intermediately just loose system fuel pressure and stall. Turns out the relay contact inside the mass air flowmeter would open and cutoff the fuel pump, I gave it a slight tweak to the right at it's base with the duckbill pliers and this kept the contact closed.

The darn thing had me fix and study every other known condition because of it working on and off condition. I thought it was a blockage and cleaned the entire fuel manifold to the gas tank.

Oh well

The second issue I had was much worse my car would intermediately just loose system fuel pressure and stall. Turns out the relay contact inside the mass air flowmeter would open and cutoff the fuel pump, I gave it a slight tweak to the right at it's base with the duckbill pliers and this kept the contact closed.

Keep in mind that this will work on 75-77s but 78s (and up) don't have fuel pump contacts in the AFM.

Keep in mind that this will work on 75-77s but 78s (and up) don't have fuel pump contacts in the AFM.

curious, because on my 78 the fuel pump runs always when the key is turned to on whether the engine is running or not, is that correct?

I shouldn't work that way. Sound like someone wired it direct to the ignition circuit for whatever reason.

I shouldn't work that way. Sound like someone wired it direct to the ignition circuit for whatever reason.

looks like you are correct as now that i look at the bad wiring in my car the relay bracket has been compleatly removed. the fusable links are gone and replaced with 30 amp fuses.

My fuel pressure drops off immediately after turning off the engine, however never fails to fire right up. Just in case I have located a Kepner inline check that I plan to try.

Whoa. Lots of options on that website. Would you mind posting exactly which check valve you went with. Thanks.