Fuel Vapor Control System; Fuel Tank Filler Cap; Charcoal Canister; Liquid Check Valve - Jeep 1979 CJ-5 Technical & Service Manual

FUEL SYSTEMS 1J-5
station pumps. The restrietor reduces the size of the
filler neck to a small opening which is covered by a trap
door. The small diameter unleaded fuel pump nozzle can
pass through the restrietor opening and push open the
restrietor trap door, allowing the fuel tank to be refilled.
In this way, the catalytic converter is protected from
contamination by leaded fuel.
The filler neck opening is located on the right rear
body panel on CJ-5 and CJ-7 models. On Cherokee and
Wagoneer models, the filler neck opening is located on
the left rear quarter panel. On Truck models, it is lo-
cated on the left side of the pickup box.
The filler neck is connected to the fuel tank inlet by a
hose secured with clamps.
All fuel tanks are equipped with a vent hose which
extends from a fitting at the top of the tank to the filler
neck. This vent relieves the air displaced as the tank is
filled.
Fuel Tank Filler Cap
The filler cap incorporates a two-way relief valve
which is closed to atmosphere under normal operating
conditions. The relief valve is calibrated to open only
when a pressure of 0.75 to 1.5 psi (5 to 10 kPa) or a
vacuum of 1.1 to 1.8 inches of Hg (4 to 6 kPa) occurs
within the tank. When the pressure or vacuum is re-
lieved, the valve returns to the normally closed position.
FUEL VAPOR CONTROL SYSTEM
The fuel vapor control system prevents raw fuel va-
pors from escaping into the atmosphere. Fuel vapors
from the fuel tank and carburetor bowl are collected in a
charcoal-filled canister and are metered into the intake
manifold for combustion. On all vehicles, a rollover
valve in the vent system prevents fuel from flowing out
of the vent lines if the vehicle is accidentally rolled over.
The various components, shown in figure 1J-6, are de-
scribed below.
Ciipiiiits
Charcoal Canister
This component is used on all models. The charcoal
canister is filled with granules of activated charcoal.
Vapors entering the canister are adsorbed onto the sur-
face of the granules.
The canister has a staged dual purge feature (fig. 1J-
7). Two inlets are provided, one for tank vapor and one
for caruretor bowl vapor. The outlet is connected to
intake manifold vacuum. The fourth nipple is connected
to the carburetor spark port (ported vacuum).
When the engine is running, manifold vacuum draws
fresh air through the inlet filter in the bottom of the
canister and purges stored vapors. When ported vacuum
reaches 12 inches Hg (41 kPa), the secondary purge
S P A R K P O R T
V A C U U M
S I G N A L
C A R B U R E T O R
B O W L
V E N T
L I Q U I D C H E C K
VALVE
P U R G E
L I N E
V A P O R
V A C U U M FILTER N S T O R A G E
S I G N A L C A N I S T E R
F U E L
F U E L T A N K
Fig. 1J-6 Fuel Vapor Control System—Typical
P O R T E D
V A C U U M
S I G N A L
F R O M
C A R B U R E T O R
T O
M A N I F O L D
V A C U U M
S O U R C E
VAPOR F R O M
F U E L T A N K
V A P O R F R O M
C A R B U R E T O R
B O W L
Fig. 1J-7 Charcoal Canister and Hoses
curcuit is opened, and the canister is purged at a much
higher rate.
Liquid Check Valve
This component is used on CJ models. The liquid check
valve permits free passage of vapors, but prevents liquid
fuel from reaching the charcoal canister. If liquid enters
the check valve, the float rises, forcing the needle into its
seat (fig. 1J-8).