Fuel pressure issue 04 XLT 3.0L

[Lord Corn]

Hello all, I've got a quick question for everyone before I pull a fuel pump.

My 2004 3.0L is having trouble building pressure during key-on/engine-off. The pump will always get power, but will only run for less than 2 seconds (usually 1-1.25 seconds). It also only builds about 5-10psi per key-on/ignition-off cycle. I eventually get it to about 35psi, then it sometimes goes higher with more key-ons, sometimes doesn't build any more pressure with key-ons (pump still runs, just no pressure increase). From what I understand, it is a returnless system, and most of the actual fuel system parts are an all-in-one fuel pump design. This leads me to buying a new pump.

I want to be sure there are no funny electrical safeties or something that could be causing this, and isn't in the tank. I have no problem doing a pump swap, but I want to make sure I have to do the work first. Any Ideas or is it pretty much 100% the pump? My guess is the regulator is weakened and shuts the pump off due to a spike in pressure or something, but either way that still means a new pump.

 

[RonD]

The computer(PCM) only runs the fuel pump for 2 seconds when key is turned on, that's normal, its for safety
At 0 RPMs pump power is limited to 2 seconds, i.e. in an accident or roll over fuel line can break, engine would stall(0 RPMs) and fuel pump would shut off, so no fuel pumping out to feed a fire
So engine RPMs limit pump power, above 400 RPMs pump will be on full time

15psi is enough to start the engine, but fuel pressure should hold above 30psi when key is off
Running pressure should be 55psi on returnless system

Yes, there is a check valve/back flow preventer in the fuel pump assembly that should hold the pressure above 30psi in the returnless system, when pump is off

 

[pjtoledo]

once it is started and running, can you do a full throttle acceleration for 0 to 70?

 

[Lord Corn]

once it is started and running, can you do a full throttle acceleration for 0 to 70?

She did 0-85 no issues, multiple times, plenty of power. The ONLY symptom is having to turn the key 6-12 times per start, once started it idles/drives perfectly fine. There is a built in rpm limit of 3,400 when shifter is in park correct? (god I hope so.) I am planning of driving it 5 miles with the guage hooked up, shut it off, then check pressure every 10 minutes until it drops off. I do not know how long it will hold pressure. I can video it if anyone is interested in seeing it.

 

[Lord Corn]

Oh yeah, fuel filter has been changed so that's good.

 

[RonD]

Yes, there is an RPM Limiter when in Park/Neutral or 0 MPH

Fuel pressure should hold for MONTHS, you will most likely have to change the fuel pump assembly if pressure is dropping to 0 psi in a few minutes.

But you should only have to turn the key on and off 3 times to get a start up from 0 psi pressure

 

[Lord Corn]

Yes, there is an RPM Limiter when in Park/Neutral or 0 MPH
Fuel pressure should hold for MONTHS, you will most likely have to change the fuel pump assembly if pressure is dropping to 0 psi in a few minutes.

Yeah it holds pressure more like minutes ha. Fuel pump will be replaced, I just wish I knew exactly what was causing it. I have no problem replacing the entire assembly as it's a unit, but I'd love to know exactly what is failing. Perhaps the removal will tell more.

 

[RonD]

The check valve or fuel pressure regulator in the assembly is leaking

Picture here: https://www.2carpros.com/images/question_images/18321/original.JPG

Not a Ranger assembly, black arrow points at pressure regulator/check valve combo unit, which is used on Single line assemblies

Rangers often have TWO line assemblies, so separate pressure regulator and then check valve in the fuel pump, either can cause loss of pressure with key off

The two line system uses a 3 port Fuel Filter, in and out, plus a return line to tank that goes to the pressure regulator

Ranger assembly seen here: https://i.ebayimg.com/images/g/stMAAOSws2RcR5ur/s-l500.jpg

You can see the two lines and pressure regulator

 

[cbxer55]

My Ranger hasn't held pressure after shut off for years. Still starts every time, first turn of the key. Put a new pump and filter in it in January 2017. Still, fuel pressure falls off as soon as the key is turned off. Next morning, turn the key, listen for the click, start engine. Vroom fires right up first turn. Lovin it! If it ain't broke, don't fix it.

My shop manual says fuel pressure should be 56 to 72 psi. Mine currently runs at 64 psi.