2000 4.0 OHV fuel pressure

[2k4dot0]

Have found dozens of posts on this but what should the fuel pressure be on a 2000 Ranger 4.0 OHV motor? This is the single line fuel rail no return. Fuel pressure gauge shows 30psi at idle and going down the road. Looks like it dips a few psi when I take off from a light.

I inherited this Ranger with 150k hard miles and have been working out the bugs - bad coil pack, intake gaskets, dead d/s front O2 sensor, new fuel filter (replaced 2x) it's gone from not running to driveable but still runs with LTFT's +25% at idle and +10% on the road. Cleaned the MAF no change. Eventually sets P0171 and 0174 codes.

 

[RonD]

Welcome to TRS


In 1998 Ford changed Rangers over to Returnless Fuel System, 1 fuel line to engine, no return line.
These systems use 65psi fuel pressure, range 60-70psi

1997 and older used a Return line with Fuel pressure regulator on the fuel rail, so 2 fuel lines in engine bay.
These systems used 35psi, range 30-40psi

If you only have 30psi at the fuel rail then either pressure gauge is wrong or Fuel Pump is not working well, could be a cracked supply line in the tank, but with Lean code gauge is probably right.
This is assuming you don't smell gas leaking from a fuel line from tank to engine.

There is also a sock/filter in the tank that could be plugged up.

Yes the Lean codes and high fuel trims could be caused by low fuel pressure.
Computer has no sensor for fuel pressure, it assumes 65psi.
So at 65psi when computer opens an injector it expects XX amount gasoline to flow into the intake.
Fuel trim number is the "open time" for the injectors.
If O2 sensor reports Lean, too much oxygen in exhaust, then computer opens the injectors longer to let in more gas, that's +1 fuel trim, then +2, and +3, until O2 reports correct oxygen level in exhaust.
When fuel trims get into the +20 range computer will set a code.

If fuel pressure is 30psi then injectors would have to be open longer to get the same amount of fuel expected at 65psi, so high fuel trims and a Lean code

 

[2k4dot0]

Thanks for confirming that - gauge is good had it on another brand truck that runs 58psi and it reads correctly. Not looking forward to dropping tank or pulling bed either choice will be a big fight with the rust monster.

The #6 (driver's side rear) spark plug was fouled with oil/deposits is there a known bug for that? The PCV is good, other plugs are clean.

 

[RonD]

Never tried it but you can get inline check valves, one-way valves.

Closer to the fuel tank would be better, like by the fuel filter.