MAF Sensor/Fuel Trim/ Vacuum Leaks

[Schurkey]

Is there fuel going back to the tank when the fuel pump isn't running?

 

[alpinecrick]

I have always had good luck with oem delco pumps vs aftermarket.

This^^^
Or Delphi........

 

[Marcos Beltran]

Is there fuel going back to the tank when the fuel pump isn't running?

How can you tell if there is and how is that possible without anything physically pushing it through?

 

[Schurkey]

Open the return plumbing closer to the regulator.

Run the pump, watch the fuel pressure gauge. It stabilizes at 61 psi, and fuel is being returned. Shut the pump off. Fuel pressure should stay at or close to 61 psi; but there should be no fuel going down the return hose.

If there's still fuel going down the return hose, pressure drops. If pressure drops with no fuel going down the return hose, it's pretty-much got to be going out one or more of the injectors.

replaced regulator with new one and still leaks pressure.

If the pump is running, of course it "leaks pressure". The pump is designed to produce more pressure than the injectors require. That's why there's a pressure regulator--to reduce the system pressure to what the engineers intend the injectors to run at.

Yes sir pulled each injector and verified. Also ports are **** dry. That was actually my next guess but the thing is i pulled the pump out to check it and the hose is brand new... ...Everywhere else is dry, metal fuel lines, rubber lines, injectors, injector lines, and regulator.

I isolated the fuel line that feeds gas to the injectors. So from the tank to the end of the fuel line right before it reaches the injectors it keeps 61 psi. So only thing left that can leak is the spider injector assembly right? Even though there is no visible fuel leakage something is causing the fuel system not to keep its pressure and all other parts have been checked twice. Thats the only logical part left.

Overall, I'm kinda mystified how the pressure can drop when everything you look at doesn't seem to be leaking. You're saying that the ports are dry, the injectors are dry, the pump holds pressure, etc.

 

[Marcos Beltran]

Open the return plumbing closer to the regulator.

Run the pump, watch the fuel pressure gauge. It stabilizes at 61 psi, and fuel is being returned. Shut the pump off. Fuel pressure should stay at or close to 61 psi; but there should be no fuel going down the return hose.

If there's still fuel going down the return hose, pressure drops. If pressure drops with no fuel going down the return hose, it's pretty-much got to be going out one or more of the injectors.



If the pump is running, of course it "leaks pressure". The pump is designed to produce more pressure than the injectors require. That's why there's a pressure regulator--to reduce the system pressure to what the engineers intend the injectors to run at.



Overall, I'm kinda mystified how the pressure can drop when everything you look at doesn't seem to be leaking. You're saying that the ports are dry, the injectors are dry, the pump holds pressure, etc.

You and me both on the mystified comment. Let me start over as to whats been done and checked and maybe you can catch something that i might have over looked. From the start i put a pressure gauge on the schrader valve and turn the key and let the fuel pump power up for the 2 seconds and then it shuts off. The gauge will jump up to 61 psi then lower almost instantly to 20 psi and then slowly taper down. It will take 15 to 20 minutes to taper down when under 20 psi. So since the pump was replaced about to months ago it was pointing towards a leaking injector or FR. So opened up the plenum and hooked the battery back up and turned the key expecting to see the FR to leak. Nothing, totally dry. So i pulled out each injector and checked each one and had my boy turn the key 2 or 3 times for each injector and still the same, no leaks. So then well it they aint leaking then it has to be the check valve in the pump right? Took the bed off the truck, pulled the pump and replaced it with new pump that was under warranty. Still the same issue, 61 psi when key is initially turned on and drops to 20 psi. So then i thought well maybe its the FR cause i was hearing a hissing noise when key was turned on. Replaced that and same issue. So i decided to isolate the fuel outlet/feed line. So from the tank all the way to the end of fhe metal line right before it goes into the spider injection i capped it off with a rubber hose and bolt. Turned the key and shot up to 70 psi then held at 61 psi for over 45 minutes. Came back 3 hrs later cause i had something to take care of and it was at 45 psi. So i can eliminate from that line to the tank as the problem. My problem exists from the spider injection on back to the tank on the return line. But as mentioned nothing is physically leaking which is causing me to pull my hair out and thats bad cause im already bald, lol. Im really out of ideas and things to check.

 

[Marcos Beltran]

Got up this morning and did some more tests to see where my leak is coming from. Im literally starting to think that maybe my fuel gauge is screwed up. Gonna get another one and see if i get the same results. At first when testing i would get 61 psi and it would quickly fall to 20 psi and slowly taper to 0 psi. So this morning i first crimped the fuel pressure line and the 1st pictures is what i got. Got 61 psi and took 20 to 30 seconds to go down to 50 psi and held steady. 2nd picture i crimped the return line and slowly tapered down to 38 psi and held steady. 3rd picture is with both pressure and return lines crimped and held steady at 50 psi Last picture was no lines crimped and held steady at 46 to 47 psi. All testing was done by manually jumping the fuel pump at the fuel pump relay and having someone crimp the line from under the truck. Again still no visual fuel leakage anywhere and tank has a new gas hose that goes between pump and sending unit.

 

[Schurkey]

Is that a liquid-filled gauge?

I see a meniscus at the top of the gauge face; I can't tell for sure if it's real or a figment of my computer screen.

 

[Marcos Beltran]

Nope, not liquid filled. Its a rental from Autozone.

 

[Marcos Beltran]

Whats this check valve for on the return line? Or is that just a union?

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[Schurkey]

The gauge still looks "liquid-filled" on my screen, but I'll take your word for it. Liquid-filled gauges are notoriously inaccurate unless burped before use to equalize ambient pressure with internal-gauge pressure. They always have a rubber plug for that purpose.

I'd expect that's just a union.