I have been struggling with a 2000 w/ 4.3 4wd that stumbles badly and nearly cuts off when starting from a stop. I have replaced the fuel pump and filter and still only get 58 lbs. of pressure. Today I pulled the plenum and found that the inside of the plenum and the manifold are black. I did not find any leaks or smell any fuel but something has caused it to carbon up. Any ideas? Also need to know how to check the poppets.

 

you checked the pressure, did you do the leak down as well? should not drop below 55psi in 10 minutes.
are their any stored codes? bring it to a parts store and have them scan to see if there are any check engine codes.

 

Pressure is 58 and holds at 55. There are no codes.

 

You need 60-66psi not 58.

 

ehhh. id say 58 is maybe ok.

Change your fuel filter and test again.

you said u replaced the pump....with what? (brand)

 

Any chance you could get your hands on a different gage?
From what I have seen most low feel pressure problems start to manifest as long crank to start time.
Like Chris said fuel filter could make it starve when you step on the gas.
It sounds strange but all carboned up and ugly is kind of what you want to see under there. Shiny spots mean you have gas spraying someplace.

 

When the EGR valve opens, it fills the entire plenum with exhaust gas, that's why it's black...perfectly normal.

If the 58psi reading is accurate, it's too low and you will have driveability issues caused by a lean mixture. As Jeff mentioned, "Any chance you could get your hands on a different gage?"

As rexmburns mentioned, with fuel pump running, engine off, pressure must be 60psi to 66psi. Must remain above 55psi for at least 10 minutes after the pump shuts off.

 

Fuel filter is newly installed, no miles on it. Used a second pressure gauge and got same results. Fuel pump is Delco. Holds pressure at 55. Is there a way to check the regulator with a vacuum pump while off the spider?

 

Not really because that fpr works in a vacuum environment under the plenum. Your going to have to get a piece from Dorman, think they call it a fuel line repair kit. Its a short connector that will give you the ability to connect your gage right to the fuel filter. If you get the correct pressure there then the fpr is opening to early.<br />


Almost positive its Dorman 800-121

 

Spittybays is exactly right. All pressure and flow from the pump must end at the gauge. The Dorman # is correct. With the pump running, pressure must be 73psi to 108psi. It must remain above 55psi for at least 10 minutes after the pump shuts off. If it passes both parts of this test, the regulator is at fault. If it fails one or both parts of the test, the pump is at fault.