Fuel Return System; Fuel Gauge; Fuel Pump; Fabricated Manometer - Jeep J-10 Series 1982 Technical & Service Manual

1J-8 FUEL SYSTEMS
NYLON
TIE
STRAP
CLEAR
PLASTIC
HOSE
WOOD
BOARD
ALL DIMENSIONS
GIVEN IN INCHES
UNLESS OTHERWISE
SPECIFIED
90566
Fig. U-12 Fabricated Manometer
(3) Remove fuel return hose (six- and eight-cylinder
engines only) from fuel filter (engine compartment) and
plug opening in filter.
(4) Remove fuel tank vapor hose from charcoal
canister.
(5) Connect plastic tube or rubber hose between
manometer and fuel tank vapor hose.
NOTE: Fuel tank must be no more than 8/4 full
CAUTION: Do not pressurize the fuel vapor control
system more than 1.5 psi or 10.3 kPa (1*1.5 inches of
water).
(6) With bicycle tire air pump (suggested maximum
pump size is 15 inches in length, 1 inch plunger diame
ter), pressurize system at fuel return hose until column
of water in manometer rises 15 inches (1.1 in. Hg or 3.7
kPa) from no-pressure position.
(7) With soap and water solution, inspect all fuel
vapor control system connections for leaks (bubbles).
Repair as necessary.
(8) Connect fuel tank vapor hose to canister and
fuel return hose to fuel filter.
FUEL RETURN SYSTEM
All Jeep vehicles with six- and eight-cylinder engines
employ a fuel return system to reduce the possibility of
high temperature fuel vapor problems. The fuel return
system is comprised of a fuel filter with a return nipple
and a return line to the fuel tank (fig. 1J-13).
The fuel return line is routed to the fuel tank, where it
connects to a nipple on the fuel tank sending unit. Dur
ing normal operation, a small portion of liquid fuel is
returned to the tank. During periods of high under hood
temperatures, vaporized fuel is also returned to the tank
and not passed to the carburetor.
The return line nipple on the fuel filter must be posi
tioned upward to ensure proper fuel system operation.
Some engine/carburetor combinations are equipped
with an inline check valve in the fuel return system near
the fuel filter. The valve eliminates any possibility of
fuel returning to the carburetor through the fuel return
line. The check valve has a stainless steel, spring-
assisted check ball that closes the orifice (fig. 1J-14). The
valve is secured by a clamp. Pressure of 0.1 to 0.6 psi
(0.68 to 4.13 kPa) at the fuel filter end opens the check
valve and permits normal operation of the fuel system.
The check valve is marked with an arrow that in
dicates the direction of normal fuel flow. If it is re
versed, the fuel return system will not function.
FUEL GAUGE
Refer to Chapter 1L—Engine Instrumentation for op
eration, malfunction diagnosis and replacement pro
cedures. Service of the sending unit is described within
Fuel Tank in this chapter.
FUEL PUMP
A single-action, stamped fuel pump is used for all
engine applications. The fuel pump is comprised of an
actuating lever, a diaphragm and spring, an inlet valve
and an outlet valve (fig. 1J-15). An eccentric on the
engine camshaft operates the fuel pump lever, which is
linked to the pump diaphragm. The lever pulls the dia
phragm to its extended position to pump fuel into the
inlet valve. Spring pressure pushes the diaphragm to
ward its relaxed position to force fuel out of the outlet
valve. When the carburetor float needle valve closes,
fuel pump output is limited to the amount that returns
back to the fuel tank through the fuel return line. The
fuel accumulated in the fuel pump chamber prevents the
diaphragm from relaxing. The actuating lever continues
to move up and down, but is prevented from operating
the diaphragm, which is held in its extended position by
fuel pressure. Fuel flow from the pump remains halted