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.

 

[S33k3r]

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.

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

 

[Matthew Jeschke]

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...

 

[S33k3r]

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.

 

[exp500]

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.

 

[Fless]

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

 

[Matthew Jeschke]

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

 

[blondie70]

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

 

[Matthew Jeschke]

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

 

[exp500]

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

Correct.

 

[exp500]

Correct. Helps to add a hose to gas can.

 

[Matthew Jeschke]

I think I just need to find an adjustable regulator that is a direct fit for factory rail. Having some trouble locating one.

After that, if pump cannot keep up, I'll order a higher volume one... Perhaps from AEM.

 

[S33k3r]

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

I don't know how viable this suggestion is, but I thought it might at least be worth thinking about:

Get some painter's plastic, you'll probably want the thick stuff. Then tape it to your vehicle where the gas comes flowing out. The plastic is to channel the majority of the gas away from you.

Alternatively, you might be able to get some of those cast savers for showering.

Anyway, gas all over is not a good thing!

 

[Fless]

Or something like this:

Flexible Oil Funnel Reusable Oil Change Funnel | EWK

Whether draining or refilling engine oil, brake fluid, transmission fluid, EWK flexible funnel would help! Simple wipe clean after use & store to fit in any tool box!

www.ewktool.com

 

[Matthew Jeschke]

Honestly, I'm thinking I'll pass on the taking fuel system apart to measure flow. Not even sure I have that spec on the pump. Really mainly looking for adjustable regulator at this point in time so I can set the pressure to what it needs to be KOEO. Then if pump doesn't keep up I will do a aftermarket pump. Pretty sure though the regulator must be wrong. I cannot get over 45PSI KOEO. Plus I'd like to boost that a bit over factory anyways...

Anybody done an adjustable regulator with the truck fuel rail? Not seeing a direct bolt on solution so not sure how to go about it.

 

[Mudsport96]

I haven't whole heatedly looked for an adjustable one. But it seems you are right as I haven't found one that goes on the factory rail. Which is hard to believe with all the other aftermarket part for these.

 

[Matthew Jeschke]

Back to fiddling with this. My gas mileage is 15 MPG at BEST. Patched a hole in exhaust (between muffler and cats). No effect. Thought maybe it'd help. Long story short I bought a $30 fuel pump and sending unit off eBay to measure the basket size. AEM in tank pumps will fit. The pump sleeve in the housing is almost an exact fit. AEM pumps are a bit shorter but that shouldn't be any issue. I've called AEM but they were only so helpful.

Their spec says 40PSI at 340LPH. That's insane flow! I believe I need no more than 200 LPH (good for over 500 hp, I might make around 400hp but want 500hp haha)... I know pump is overkill but it's cheaper than a lower flow one and don't really want some generic pump which is well peanuts to buy.

My question is what is our factory fuel line size, 3/8"??? I think it all comes down to line size and the pressure regulator? From that along with voltage, I think but am not sure how, you can get PSI in the line prior to the regulator? **UPDATE**: Answered my own question LQ9/LM4/LM7 ID fuel supply is 0.334" OD 0.374" which is 3/8".

I have a return style system (not the newer return-less).


Link to fuel pump calculator HERE

 

[Matthew Jeschke]

Anybody know what gauge wire the factory puts to the fuel pump?

Guy recommended 12 gauge wire from AEM. I think I'm just going to order 12 Gauge wire but not sure where to get automotive wiring... how many strands are in it, etc.

 

[Matthew Jeschke]

Wallet is now $200 lighter. Ordered pump and misc parts. I think the factory pump wiring is 14 gauge. Unless somebody knows for sure.