I checked fuel pressure yesterday with the engine idling. It was 29 PSI which is within spec, so that's good. I then shut off the engine and observed pressure drop. The pressure dropped from 29 to 25 PSI after one minute, and dropped further to 20 PSI after about 6 minutes, and was at 10 PSI after an hour.

Is this normal/acceptable, or do I have a fuel leak I need to chase? If I'm dealing with a leak, is the most likely culprit the fuel pump check valve, or a leaky injector, or?

Thanks in advance!

that seems pretty quick. it could be the pressure regulator, if you dont see a leak or smell a leak anywhere maybe the check valve, all possibilities..
t
not long ago i noticed this and found a leaking hose connection at one of the injectors

assuming you are still fuel injected...
are you using the 2 port pump... or the 3 port pump?

the 3 port pump also functions as a fuel accumulator
it has a rubber seal inside that can age out

do you have to crank the starter 4 times or more to get it to start when cold?

the accumulator feature keeps the pressure up, so that the car can start more quickly and doesn't have to build up pressure before it will fire...


brant

My 73 still has the original 3 port pump in the original location. My pressure does about exactly what yours does, starts on just a touch of the key regardless of the pressure at the time. Even in the morning when cold. Not saying that loss of pressure is the way it should be, just doesn't seem to affect my start up. Even after the car sat for 2 months it maybe cranked over 3 times before firing up. I think for the 2.0 where the pump fires up early it isn't as such a big deal.

Yes, the car has the original D-jet injection system. And the pump is a 2 port pump. The engine starts in less than four cranks when engine is cold or warmed up.

Does the 2 port fuel pump have a check valve? I think I have documentation from the PO on the 2 port fuel pump that he had installed.

Not sure if this is relevant, but I also did a pump test with the pressure side fuel line connected to tygon tubing which went into a gas can. I did observe tiny air bubbles in the fuel, making me think there may be an air leak some where in the system.

I don't believe the 2 port has the check valve built in... other than the pump itself.

If you have a Bosch 2 port pump, the check valve looks like this.

it is quick.
during recommission of my 74 1.8 we installed a new two port pump in location of old pump near engine underneath. i was holding 20 psi at end of day after a start in morning. admittedly L jets have slightly higher pressure in line at 35 to start with.

its possible your fuel pressure regulator is leaking down rather than the pump.
but it could just as easily be the pump and its check valve.

you can install an inline check valve after the pump and do a test.
pretty cheap to buy and fit just to do the check up.
that will tell you which one it is.

how old is your fuel pressure regulator.
might be handy to have a spare sitting around for just in case.

I don't see it mentioned in the thread...
so the other possible source of a leak can be the injectors.

you may want to pull all 4 and do a spray test...
then monitor for injector leak while they are out and the key is off (pressure dropping)

Thanks Brant. Yup, the injectors are near the top of my to-do list. If they seem sketchy at all, I'm going to send them to Mr. Injector for reconditioning and replace them if they can't be revived. Doug