5.7 vortec long crank

[slow_c1500]

Follow the hose coming from the fuel filter towards the front. There should be a rubber section.

Ok. And if I clamp this hose and the pressure does or doesn’t drop, what will it mean?

 

[Caman96]

Clamp the hose coming from the pressure side of the pump. Clamp the hose on the return side of the regulator. See if the pressure still drops. If it does, it has to be an injector.

 

[slow_c1500]

Ok so there are 2 rubber fuel hoses: one is in line with the fuel filter, and the other one isnt. I’m guessing the one that’s in line with the fuel filter is the inlet, and the other is the return line?

And would it be safe to pinch these lines with a radiator hose block-off clamp tool?

 

[slow_c1500]

ok I did the test and here’s what I found:

-Loses pressure slowly with both hoses clamped

-Loses pressure with inlet hose clamped

-holds pressure with return hose clamped

 

[Schurkey]

-Loses pressure slowly with both hoses clamped

-Loses pressure with inlet hose clamped

-holds pressure with return hose clamped

Contradictory. Doesn't make sense.

Losing pressure with both hoses clamped has to be one or more injectors.

Loses pressure with both hoses clamped, but doesn't lose pressure when just the return hose is clamped. Something is wrong with the test procedure.

Holds pressure with the return hose clamped kinda rules-out the check valve in the fuel pump, and the injectors.

 

[slow_c1500]

Not sure if this really matters, or if it could cause any error in the pressure readings, but this was my process:

I set my phone up to record the fuel pressure gauge so I could look at it later. Then i primed the key twice to get max pressure, and then I quickly got under the truck and clamped the hose(s) with pliers and held it there for a minute or so.

I did each test twice. Both times, it lost pressure with inlet line clamped, and held pressure with return line clamped. However for clamping both hoses, the first time it slowly dropped, and the second time it kinda went up and down but stayed around the same psi as when the pump initially shut off. Maybe this is human error on my part, and I was not clamping one of the hoses all the way the entire time.

 

[slow_c1500]

But since it holds pressure with the return line clamped, and that rules out injectors and check valve, does that mean the regulator is my problem child?

 

[Schurkey]

Yes, it's looking like the regulator is leaking, and MAYBE the injector(s) are intermittent. But I wouldn't get too involved in replacing stuff just yet.

I'd repeat the testing until I got non-contradictory results, or I convinced myself that some of the leaks are intermittent.

I might also throw a bottle (or two) of Techron Complete Fuel System Cleaner in the tank, fill up only at Top Tier gas stations, and drive it for a couple weeks to see if the cleaner removes any deposits that are causing leakage.

 

[slow_c1500]

Ok I have some more info after doing further testing. It turns out that it does actually lose pressure when the return line is clamped, just pretty slowly.

Also worth pointing out: with either the inlet hose clamped, or both hoses clamped, as soon as I let go of the pliers, the psi instantly dropped about 12 psi.

When I did the test with the return hose clamped and let go of the pliers, the psi didn’t drop. It basically behaved the same as if nothing was clamped.

I did the calculations and the psi dropped the fastest when either the inlet hose or both were clamped. For both of them, it took ~30-35 seconds to drop 1 psi (not including the instant 12psi drop after releasing clamp). The psi dropped considerably slower with nothing clamped, or only return hose clamped.

Bottom line: whatever is leaking, it leaks faster when you pinch the inlet hose or both hoses.

 

[1990Z71Swede]

Ok I have some more info after doing further testing. It turns out that it does actually lose pressure when the return line is clamped, just pretty slowly.

Also worth pointing out: with either the inlet hose clamped, or both hoses clamped, as soon as I let go of the pliers, the psi instantly dropped about 12 psi.

When I did the test with the return hose clamped and let go of the pliers, the psi didn’t drop. It basically behaved the same as if nothing was clamped.

I did the calculations and the psi dropped the fastest when either the inlet hose or both were clamped. For both of them, it took ~30-35 seconds to drop 1 psi (not including the instant 12psi drop after releasing clamp). The psi dropped considerably slower with nothing clamped, or only return hose clamped.

Bottom line: whatever is leaking, it leaks faster when you pinch the inlet hose or both hoses.

Although all of that does not make total sense, one thing is obvious, there is a leak.
I think we can disregard the check valve in the pump, althoug the 12psi drop could be indicative of it not seating fully, on the other hand, slower pressure drop when not clamped says the opposite.

Anyways If that was the problem it would start just fine if you let it prime for two seconds, neither are your symptoms consistent with a vapor lock caused by low fuel pressure and heatsoak.

The wet plug in #7 is a clue, are you sure it is fuel? IE does it burn if you put a match to it?

If so, try @Schurkey's suggestion first, if that does not work... I'm afraid the next step has to be opening things up again...

Also I would start questioning the fuelfilter and the possibility of contamination in the fuel lines, causing your new injectors to malfunction.

I'm surprised that what is probably a fairly small leak could have such Impact on starting... that is the reason I suggested trying to start it without injectors connected or without pressure in the line. Just to verify that the actual problem IS to much fuel...

I think unplugging the Pump or dumping the fuel into a bucket is the only way to be absolutely certain that the computer does not detect the shenanigans

And, before you ask.
NO, trying to start it while deadheading the fuelpump into a clamped fuel line is not a good idea...