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Solved What's that on the fuel rail? - Fuel Pressure Regulator - FPR

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2000StreetRod

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Year, Model & Trim Level
00 Sport FI, 03 Ltd V8
Depending on the year of vehicle there can be three different items mounted on your fuel rail with a vacuum hose connection.

For V6 Explorers/Mountaineers thru 1998 with the return fuel system a fuel pressure regulator is mounted on the fuel rail.
FPReg.jpg


For V8 Explorers/Mountaineers thru 1998 with the return fuel system a fuel pressure regulator is mounted on the fuel rail.
1996FPR.jpg


It adjusts the fuel pressure according to engine vacuum (load) and returns excess fuel to the fuel tank via a separate fuel line. According to my Haynes Repair Manual the fuel pressure at idle should be 30 to 45 psi with the vacuum hose attached and 40 to 50 psi with the hose detached.

For V6 Explorers/Mountaineers from 1999 thru 2003 with the returnless fuel system (fuel pressure regulator mounted in fuel tank) a fuel pressure damper is mounted on the fuel rail.
FPDamper.jpg


For 4.6L V8 Explorers/Mountaineers from 2002 thru 2003 with the returnless fuel system a fuel pressure damper is mounted on the fuel rail.
2003FPDamper.jpg


It smooths the pulses from the intank fuel pressure regulator. According to my 2000 Explorer shop manual the fuel pressure should be 65 psi +/- 8 psi.

For V6 Explorers/Mountaineers from 2004 with the returnless fuel system a fuel pressure/temperature sensor is mounted on the fuel rail.
FPSensor.jpg


It allows the PCM to monitor the fuel pressure and temperature at the fuel rail and control the fuel pressure. According to the 2004 Explorer/Mountaineer Workshop Manual the fuel pressure should be 30 to 40 psi with ignition on and engine running or not running.

All of the above devices utilize a diaphragm that can rupture with age. When that happens there are consequences: the fuel pressure rapidly drops when the fuel pump isn't running; and fuel is leaked into the intake manifold resulting in a rich mixture when the engine is running (vacuum present).

The check valve in the fuel pump assembly is fairly reliable and if functioning properly will hold pressure for many hours. My fuel pressure only drops from 67 psi to 30 psi in eight hours. If there is a rapid drop in fuel pressure I would test the rail mounted device first. It is easier to access and test, and less expensive to replace.

Edit: added information on V8 models

FPDamper.jpg


FPSensor.jpg


FPReg.jpg


2003FPDamper.jpg


1996FPR.jpg
 






Great info!
 












Dons analysis here is so valuable - getting ready to rework my manifolds and I found that the dampener listed above for 99 up made it into some late build 98 4.0 sohc - std motor products selling it for 249 tells me they make it with gold nickel braze - lol

5DBD9A34-3046-4412-B0E1-51A9B124A012.jpeg
 






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