Incorrect fuel pressure Key on and Engine Running

Matthew Jeschke said:

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.

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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.

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.

Matthew Jeschke said:

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.

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Were you ever able to resolve this? If so, could you please share how?

Have yet to get it resolved. Got really busy, starting a new business. Back to topic at hand.

A friend used to build these trucks for GM in Detroit. He has what I'm considering the solution but I cannot find a good part to easily do this w/o modifying the fuel system.

He said to get an adjustable fuel pressure regulator. I've used those before and they work great, however, I cannot find one that's a direct bolt on. In the past I put one on my LT1 and the regulator if memory serves me correctly was prior to the rail. This truck regulator is integrated in the rail making it hard to find a direct bolt on. Does altitude / atmospheric pressure affect pressure in the fuel rail!?!? I'm at 2800ft MSL.

One question I have is KOEO pressure is low. Somebody told me that's the reference pressure (highest pressure you'll get to the rail). Makes sense. However, the guy quoted altitude. I don't see how that would affect rail pressure as the system is enclosed / no reference to atmospheric pressure? If altitude matters then maybe that's my issue.

However, either way, my MPG SUCKS horribly. I'm assuming this is not helping that. I'm getting like 12 to 14 MPG. Prior I was getting 15 to 19 MPG. Same 6.0L motor. So I'm super confused. I did however, change the pump out...

If it is an altitude issue, that is easily tested. Take a weekend trip somewhere of sea level altitude, or even below sea level, and see what happens.

Have you done a timed fuel flow test? I always did them at fuel filter because of easiest to acess, so subtract a few pounds for line restriction further toward injectors. I expected to see 2-3x minimum flow on a return line system dumping to can.

I wouldn't think altitude has any effect. Measurements I've made at 6,000' have been consistent with the published specs.

exp500 said:

Have you done a timed fuel flow test? I always did them at fuel filter because of easiest to acess, so subtract a few pounds for line restriction further toward injectors. I expected to see 2-3x minimum flow on a return line system dumping to can.

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I have not. You disconnect the fuel filter and turn the ignition on? Collect fuel in bucket or something?

Uh Oh....that fuel filter unhooking again !!!!

I hope you don't get a gas bath again....I read your story. I got an earful of gas one time.....boy, that hurt !!!!! good luck

@blondie70 Amen to that. It sucked.yhe skin pealed off my arm. It burnt horribly.