3
Operating Instructions and Parts Manual
27167
10/18
2018 OEM
®
FUEL PRESSURE
TEST KIT
10/18
2018 OEM
®
FUEL SYSTEM COMPONENTS
It is a good idea to understand how the fuel system
components work and how they relate to one another
before doing any fuel pressure testing. The fuel pump
pumps fuel from the fuel tank to the fuel pressure regulator
and fuel injectors. The fuel pressure regulator divides fuel
between the pressure line and return line. The fuel in the
pressure line goes to fuel injectors, while fuel is returned to
fuel tank through the return line.
Fuel Tank: A large container that holds vehicle’s supply of
fuel.
Fuel Pump: An electric motor that pumps fuel into the fuel
system at a constant pressure. It is mounted in the fuel
tank or on the frame. Some vehicles have more than one
fuel pump.
Fuel Pump Filter: A filter that is usually located in fuel
tank. Its function is to prevent foreign particles from
reaching the fuel pump. A clogged or restricted fuel pump
filter can cause low fuel pressure readings. When replacing
a fuel pump it is a good idea to replace the fuel pump filter.
Return Line: Path way for excess fuel to return to the fuel
tank.
Pressure Line: A pressurized fuel line that carries fuel from
the fuel tank to the fuel injectors.
Fuel Filter: A filter that is located in-line with the pressure
line. Its function is to prevent foreign particles from
reaching the fuel injectors. A clogged or restricted fuel filter
can also cause low fuel pressure readings. This is the only
fuel system component that requires periodic replacement.
Refer to vehicle owner’s manual for replacement interval.
Fuel Rail Test Port: A Schrader valve located on the
fuel rail that allows easy connection of a fuel pressure
gauge to measure fuel pressure. Do not confuse this valve
with the Schrader valves that are used for recharging air
conditioning systems.
Fuel Pressure Regulator: The fuel pressure regulator
is connected across the pressure line and return line. It
contains a spring-loaded valve assembly that opens to
allow fuel to move into the return line, when the pressure
line fuel pressure is exceeded. It is used to keep a
constant fuel pressure drop across the fuel injectors.
Some fuel pressure regulators have a vacuum port so fuel
pressure can be adjusted based on engine load. These
are commonly called vacuum actuated (compensated)
fuel pressure regulators. A leaking fuel pressure regulator
can cause low fuel pressure readings and hard starting
problems.
Fuel Rail: The fuel rail assembly is bolted to the intake
manifold. Its purpose is to hold the fuel injectors in place
and to deliver pressurized fuel to the fuel injectors.
Fuel Injectors: A precision valve that is controlled by a
solenoid. Fuel injection is controlled by the amount of fuel
pressure, and the size and duration of the valve opening.
Fuel injectors contain a filter used to prevent very small
particles from clogging the valve. Leaking fuel injectors will
cause fuel pressure to slowly decrease when the ignition
key is on and engine is off.
