Fuel Pump Pressure Test

NOTE: Begin basic fuel system diagnosis with testing fuel pressure.

When ignition is turned on, or when the engine is turned off, fuel pump will run for 2 seconds. In-tank fuel pump will run when PCM is receiving reference pulses with engine running or cranking. PCM controls fuel pump operation. Fuel is supplied to injectors through an in-line fuel filter to a pressure regulator, attached to lower manifold. Fuel is supplied at a pressure above regulated pressure needed by the fuel injectors. Fuel pressure regulator keeps fuel available to fuel injectors at a regulated pressure. Unused fuel is returned from fuel pressure regulator back to fuel tank through a fuel return line.

Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Install fuel pressure testing gauge on fuel filter output side of pressure line. See Fig 1 . With ignition on, fuel pressure gauge should read 41-47 psi (2.8-3.3 kg/cm² ).

A fuel system that cannot maintain a constant fuel pressure reading has a leak in one or more of the following areas:

Fuel delivery lines and/or fuel filter.
Fuel pump check valve.
Fuel pressure regulator.
Fuel injector(s).

Fig 1: Installing Fuel Pressure Gauge (Hombre)

Courtesy of ISUZU MOTOR CO.

FUEL PUMP PERFORMANCE

Engine Application

Unregulated Pressure psi (kg/cm² )

Regulated Pressure psi (kg/cm² )

Hombre

⁽¹⁾ 41-47 (2.8-3.3)

⁽²⁾ 31-44 (2.2-3.1)

⁽¹⁾	With ignition on and vacuum hose disconnected from pressure regulator.

⁽²⁾	With engine at idle or with 12-14 in. Hg vacuum manually applied to pressure regulator.