Wagoneer L6-258 4.2L VIN C 2-bbl (1982)
Evaporative Emission Control Canister: Description and Operation
The fuel resistant nylon body of the canister contains activated charcoal granules which absorb and store fuel vapors until they are drawn into the
induction system to be burned along with the normal air fuel mixture. Outside air is drawn into the canister through a replaceable filter pad located
at the bottom of the canister.
1971-1973
On 1971-72 models and 1973 models with 6 cylinder engine, a purge valve is located at the top of the canister and is connected by hoses to the
fuel tank vapor line, PCV vacuum hose and carburetor ported vacuum line. During idle or heavy load operating conditions when manifold ported
vacuum is less than 12 inches Hg., the purge valve is seated and vapor flow from the canister is limited to 5-10 cubic feet per hour through a small
orifice in the purge valve opening.
During cruise speed operating conditions when ported vacuum is at least 12 inches Hg., the purge valve opens and uncovers a large orifice in the
center of the valve housing. The combined vapor flow between the small and large orifices is 40-50 cubic feet per hour.
On 1973 models with V8 engines, the canister does not have a purge valve and has only two hose connections. One hose is connected to the fuel
tank vapor line while the other is connected to the underside of the air cleaner snorkel which extends into snorkel opening. Fuel vapors are drawn
from the canister by the vacuum created as incoming air passes over the tube in the air cleaner snorkel. The vapor flow from the canister is
proportional to the air velocity in the snorkel opening.
1974-77
On 1974 models and 1975-76 models with V8 engine and 2 barrel carburetor, the canister connections and operation is the same as 1973 models
with V8 engines. However, the hose connected to the fuel tank vapor vent line has a metering plug.
On 1975-76 6 cylinder and V8 with 4 barrel carburetor and all 1977 models, the canister has three nipples. On V8 engines with 4 barrel carburetor
and 1975-77 models with 6 cylinder engine, one nipple on the canister is connected to the fuel tank vapor vent line, one is connected to the
carburetor float bowl and the other is connected to the underside of the air cleaner snorkel.
On 77 models, the line from the fuel tank vapor vent line fits over a small metering plug which seats against the canister nipple (use care to avoid
losing plug if line is disconnected). The tube connected at the underside of the air cleaner snorkel projects into the incoming air stream of the
snorkel. Air passing over the tube creates a partial vacuum that draws fuel vapor from the canister. The amount of vapor drawn is relative to air
velocity passing through the air cleaner snorkel
1978-82
On 1978-82 models, the canister has a staged dual feature and four nipples. Two of the nipples are inlets, one for fuel tank vapor and the other for
carburetor float bowl vapor. The other two nipples are outlets, one is connected to intake manifold vacuum while the other is for carburetor ported
vacuum. When the engine is running, manifold vacuum causes fresh air to enter through the inlet filter in the canister and purge the stored vapor.
When ported vacuum increases due to increased throttle opening, the secondary purge circuit is opened and the canister is purged at a much higher
rate.
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