Fuel pressure spec

[jtaborsky]

What's considered acceptable fuel pressure? I have about 27psi at idle, which is low according to what I can find. Can anyone confirm?

 

[RonD]

1986 to 1997 Rangers used 30-40psi with engine running
1998-2011 used 50-60psi

27psi shouldn't cause any running issue for an 1986 to 1997 Ranger, it would cause issues for 1998-2011

Raise RPMs to about 2,000 and hold it there, and watch pressure, if its slowly dropping then there is an issue
Turn off engine
Have some one cycle key on and off while you watch the pressure
Each key on and off should raise the pressure by 10psi or so, until it gets just above 40psi and it will not go higher
The Fuel Pressure Regulator(FPR) on the engine is set for 43psi, so it should not go much above 40psi, if the FPR is working OK
FPR has a Fuel line AND a vacuum line attached check the vacuum line for gasoline, replace FPR if gas is found, its leaking


Each time you turn on the key the computer runs the fuel pump for 2 seconds, and 2 seconds only, but it does this EACH TIME you turn the key from off to on, that's why you need to cycle the key on and off

 

[jtaborsky]

1986 to 1997 Rangers used 30-40psi with engine running
1998-2011 used 50-60psi

27psi shouldn't cause any running issue for an 1986 to 1997 Ranger, it would cause issues for 1998-2011

Raise RPMs to about 2,000 and hold it there, and watch pressure, if its slowly dropping then there is an issue
Turn off engine
Have some one cycle key on and off while you watch the pressure
Each key on and off should raise the pressure by 10psi or so, until it gets just above 40psi and it will not go higher
The Fuel Pressure Regulator(FPR) on the engine is set for 43psi, so it should not go much above 40psi, if the FPR is working OK
FPR has a Fuel line AND a vacuum line attached check the vacuum line for gasoline, replace FPR if gas is found, its leaking


Each time you turn on the key the computer runs the fuel pump for 2 seconds, and 2 seconds only, but it does this EACH TIME you turn the key from off to on, that's why you need to cycle the key on and off

Thanks for the detailed explanation. I've got codes for fuel pump relay primary circuit and hego fault/lean.

Sounds like i have an ignition problem to chase down.

 

[RonD]

Fuel pump "primary circuit" is the Fuel Pump Relay on/off which is controlled by the computer
(secondary circuit is the 12v power going thru relay and out to the fuel pump, just FYI)

With key on the Fuel Pump Relay's coil gets 12volts, the computer grounds the coil for 2 seconds, activating the relay

If computer doesn't "see" 12volt on its ground wire to fuel pump relay with key on it will set that "primary circuit" code
So code can be set if relay was unplugged and key was turned on or if the wires are corrode in relays base, or of course if the relay is bad

In 1987 the relay will be on inner fender and have a GREEN base, and not at all unusual for wires to get corrosion

O2 sensors only last 100k miles or 12 years and they start to show FALSE LEAN, so MPG goes down bit by bit, and after you have spent a few hundred DOLLARS on wasted fuel they will eventually set a lean code, lol
So really good idea to just replace O2s at 100k or 12 years, and keep that extra money in your pocket

In your case lean code could be fuel pressure related, but O2s do wear out, only sensor that does