Hello! I'm new to the forum. Thank you so much for this awesome resource. I've had my 1999 XK8 for many years and usually love it. LOL. My car has been starting hard. I recently (miles, not time) changed the fuel regulator and the fuel pump. The regulator had started leaking, and I assumed the pump was bad because the fuel rail is not keeping pressure when I shut the car off. Here is what I have checked so far and where I'm at. The pressure at the rail from the Schrader valve is 40 or more psi when the car is running, but goes to 0 psi as soon as I shut it off. Also, I don't get any pressure at the rail unless the car is running. Is that correct? It seems to me by just switching the key to the run position I should get pressure. I can hear the pump running. I replaced the regulator and the pump, and there are no leaks. I am assuming that the injectors are leaking down. I also have only put 1.25 gals of gas in it since the pump. Should I fill it more before I move forward. I didn't want to fill it just in case I have to drop the tank again. I'm considering replacing the injectors, perhaps one or more of them is leaking down? Thanks so much for the help.

 

I doubt your injectors are leaking down. You can pull a plug after your pressure drops and see if they are soaked with gas. My best guess is you have a bum fuel pressure regulator or bum pump. The pressure should be in the 40 PSI range with engine running. I've heard different numbers. When you turn the car off the pressure should maintain for quite some time. And yes, when you turn the ignition on the pump primes and you will see pressure at the rail. If you don't it's back to bad pump or bad regulator.

What brand regulator did you install?

 

Thank you for the response. I'm not sure what brand regulator I got. I replaced it a couple of years ago. I' may have only replaced the o rings. It was leaking gas, so I know I took it off. I have been busy with life and haven't really driven the car much in the last couple of years. The pump I put in was a Delphi. I am getting about 40 psi with the engine running. I did fill the tank today and drove it about 15 miles. I will check the pressure again tomorrow if I have time. I suppose it is possible that my gauge is leaking down after I shut the car off. It seem to me when I checked it before when I decided it needed a pump it took some time to leak down. The car does run great and very smooth, so I had my doubts about the injectors, but they are old. I'm not thrilled about taking the pump out again, but at least I know how to do it.

 

From your problem description, I'd look at the regulator first.