Fuel pressure leakdown? Options

[Robson51]

Car is a '74 2.0 with original D Jet injection.

Having a bunch of weird problems, and learning as we go about this FI. Decided to go back to the basics and put a fuel pressure gauge on it. Gauge is just before the first fuel rail.

When you turn the key on, the fuel pump activates and jumps to 28 PSI, but the minute the activation stops, it drops to 18 PSI. Fired up the car and it holds at 28.

Clamped off behind the fuel pressure regulator, and it still went from 28 to 18.

One spark plug is consistently wet-#4. All injectors were rebuilt. Has 130 lbs of compression and spark. New Pertronix, cap rotor and wires. All other cylinders look normal.

Is the fuel pressure drop normal? Or is it indicative of a leaking fuel pump check valve or leaky injector?

Thanks-

[76-914]

Car is a '74 2.0 with original D Jet injection.

Having a bunch of weird problems, and learning as we go about this FI. Decided to go back to the basics and put a fuel pressure gauge on it. Gauge is just before the first fuel rail.

When you turn the key on, the fuel pump activates and jumps to 28 PSI, but the minute the activation stops, it drops to 18 PSI. Fired up the car and it holds at 28.

Clamped off behind the fuel pressure regulator, and it still went from 28 to 18.

One spark plug is consistently wet-#4. All injectors were rebuilt. Has 130 lbs of compression and spark. New Pertronix, cap rotor and wires. All other cylinders look normal.

Is the fuel pressure drop normal? Or is it indicative of a leaking fuel pump check valve or leaky injector?

Thanks-

I'd suspect the pressure regulator and the leaking injector. Probably just the injector though.(IMG:style_emoticons/default/beerchug.gif)

[Robson51]

Car is a '74 2.0 with original D Jet injection.

Having a bunch of weird problems, and learning as we go about this FI. Decided to go back to the basics and put a fuel pressure gauge on it. Gauge is just before the first fuel rail.

When you turn the key on, the fuel pump activates and jumps to 28 PSI, but the minute the activation stops, it drops to 18 PSI. Fired up the car and it holds at 28.

Clamped off behind the fuel pressure regulator, and it still went from 28 to 18.

One spark plug is consistently wet-#4. All injectors were rebuilt. Has 130 lbs of compression and spark. New Pertronix, cap rotor and wires. All other cylinders look normal.

Is the fuel pressure drop normal? Or is it indicative of a leaking fuel pump check valve or leaky injector?

Thanks-

I'd suspect the pressure regulator and the leaking injector. Probably just the injector though.(IMG:style_emoticons/default/beerchug.gif)

Pressure regulator I think is good because of the running fuel pressure stable at 28 lbs.

[JamesM]

Is the fuel pressure drop normal? Or is it indicative of a leaking fuel pump check valve or leaky injector?

Its normal.

If pressure is still holding at 18 after the key is off than most likely nothing is leaking/bleeding pressure. From what I have seen, a key on cycle like that will cause 2 of the injectors to also activate (which ever bank the injection points are currently activating) which accounts for (at least some) of the pressure bleed down. If you want to test for leaky injectors you need to pull all 4 injector leads off to avoid activation.

If the injectors are not leaking and you are hitting 28 psi with the pump on you should be good to go.

I have found that often times when i have suspected d-jet to be the problem it winds up being something else, which is usually either ignition or vacuum/CCV related.

[brant]

also the stock 3 port pump design has an internal fuel pressure relief.

the rubber on them will fail from age.
I opened one, and rebuilt it...

my car would bleed down, not start on the first crank
I had to key my car on 2-3 times, to build pressure from the front pump to the engine to get it to start on the first try

once the seal was replaced, and the pump rebuilt... it would hold pressure for some time, and always start on the first try

brant

[Robson51]

Is the fuel pressure drop normal? Or is it indicative of a leaking fuel pump check valve or leaky injector?

Its normal.

If pressure is still holding at 18 after the key is off than most likely nothing is leaking/bleeding pressure. From what I have seen, a key on cycle like that will cause 2 of the injectors to also activate (which ever bank the injection points are currently activating) which accounts for (at least some) of the pressure bleed down. If you want to test for leaky injectors you need to pull all 4 injector leads off to avoid activation.

If the injectors are not leaking and you are hitting 28 psi with the pump on you should be good to go.


I have found that often times when i have suspected d-jet to be the problem it winds up being something else, which is usually either ignition or vacuum/CCV related.

Hadn't thought about a couple injectors being activated. The wet plug bothers me, especially with literally everything on the ignition being new and properly seated. I'm still thinking there are injection problems, just working through all the components one at a time.

Thanks-