Fuel Lift Pump - Hummer H1 Service Manual

3-2 Fuel, Emissions, and Exhaust

Fuel Lift Pump

The fuel lift pump is located on the firewall near the drivers
side of the engine. The electric fuel lift pump has a hollow
plunger that slides in a bore located in the center passage be-
tween the inlet and outlet ports (Figure 3-2). An inlet valve is
mounted on one end of the hollow plunger, and an outlet valve
is positioned at the outlet end of the center passage. Both
valves are closed by spring force.
The lift pump is designed to move fuel under a low (suction)
pressure from the fuel tank and deliver it through the filter to
the transfer pump, inside the fuel injection pump. To operate
correctly, the injection pump must have fuel at the correct pres-
sure and without air bubbles.
The lift pump is checked as part of the fuel supply system diag-
nosis. The lift pump should deliver fuel with a minimum vol-
ume of one half pint (0.24 liter) in 15 seconds and tee'd in at
the injection pump fuel inlet connection running at idle, with a
pressure of 5.8 to 8.7 psi (40 to 60 kPa). The lift pump suction
line from the fuel tank must be air tight for correct operation of
the injection pump. Any air present in the fuel system will
cause runability problems and possible diagnostic trouble
codes (DTCs) to be set in PCM memory.
Figure 3-2: Fuel Lift Pump Construction
_____________________________________________
FUEL
INJECTION
PUMP
TANK SELECTOR
INJECTORS
ELECTRIC
FUEL
FUEL
FILTER/
LIFT
WATER
PUMP
SEPARATOR
Figure 3-1: Fuel Supply System
FUEL
LINES
TANK AUXILIARY
MAIN
TANK
The electrical circuit for the lift pump involves several main
components (Figure 3-3). A relay mounted in the exterior fuse
box, and the lift pump itself, mounted near the filter on the left
side of the engine compartment.
When the driver moves the ignition switch to the "RUN" posi-
tion, the lift pump relay is energized by the PCM for 5 to 20
sec., depending on PCM time out.
As soon as the PCM receives RPM signals from the EFI pump
the relay is energized again. The lift pump remains running as
long as the engine runs.
TO FUEL
SELECTOR SWITCH
787 GY
B
FUEL
LIFT
PUMP
M
A
G2
Figure 3-3: Fuel Lift Pump Electrical Circuit
FUSE 2D
20A
INTERIOR
C1-10
537 OR
FUEL PUMP
RELAY
EXTERIOR
FUSE BOX
787 GY
G2
C27-D5 C27-D8
FUEL LIFT FUEL PUMP
PUMP SIGNAL RELAY CONTROL
POWERTRAIN
CONTROL
MODULE
9-S12-051
®