Incorrect fuel pressure Key on and Engine Running

[strutaeng]

So I did what you said. I found a way to disconnect and cap the return line. I put on a test gauge.

It got up to 80psi priming the pump w/ return blocked off.
The Pressure bled down quickly but I couldn't see any leaks in the line set.

I then put the return back on, and took off the rail (raised it above the intake). I put paper towels under each injector.

Not a single drip of fuel under any of the injectors.
Now pump only primes to KOEO around 45PSI.

I'm studying this...

It seems the drop in pressure from 85 would be correct. It should have a backup relief valve in the pump itself.

Interesting. So it sounds like the checkball is bleeding pressure back into the pressure line itself after shut-off, no? You've definitely eliminated the injectors and FPR as possible pressure drop sources.

I'll be honest and admit I've never replaced a fuel pump before (and didn't know how they operate or the components). But it looks like it's that little rubber round seal with the spring is what that it is on that video. It kinda looks like a kitchen/bath faucet seat/seal. Somehow I thought that was on the return line, but it makes sense it's on the pressure line side.

 

[Matthew Jeschke]

I'm 100% sure this pump isn't built to spec now. I'm looking at in tank fuel pump replacements. I think when I get back from my vacation I'll be swapping one into the sending unit. Seems a little bit **** retentive as I could tune around the lower pressure. However, it'll adversely affect fuel economy. If anything I'd like a higher pressure pump than a lower pressure one. Looks like our lines support up to 75PSI peak. I'd like say a 65 PSI pump or something like that. Factory is 62 PSI for gasoline, and I think 45 to 50 PSI running (don't recall where I saw that). I'm getting 48 PSI KOEO and 40 to 45 PSI running.

Maybe they installed the wrong pressure reliefs in the pump but whatever it is this Delphi pump isn't to spec. It's not even to the spec sheet they advertised it with. Maybe it's a defect... But two in a row? I think they're confusing parts in production and or merged the parts into one and didn't update their marketing. Still talking with Delphi maybe they'll shed some light on it.