Evaporative Emissions System: Description and Operation

Fig. 65 Purge valve type canister. 1985-87 4-151 engines w/fuel injection:

Fig. 66 Charcoal canister. 1987 4-151 & V6-173:

Fig. 67 Evaporative emission control system. 1987 V6-173:

Fig. 68 Charcoal canister. 1986 V6-262:

Fig. 69 Charcoal canister. 1987 V6-262, V8-305, 350 & 454 except high altitude:

Fig. 70 Charcoal canister. 1987 V6-262, V8-305, 350 & 454 high alt.:

These systems Figs. 65 through 70, transfer fuel vapor from the fuel tank to an activated charcoal canister to hold the vapors when vehicle is not running. When engine is running, fuel vapor is purged from the charcoal canister by intake air flow and consumed during normal combustion. The fuel tank has a non-vented fuel cap and a single vent pipe to the canister.

Fig. 69 Charcoal canister. 1987 V6-262, V8-305, 350 & 454 except high altitude:

Fig. 70 Charcoal canister. 1987 V6-262, V8-305, 350 & 454 high alt.:

1987 V6-262 & V8-305, 350 & 454 Engines
On models except high altitude, the canister, Fig. 69, is purged whenever the engine is operating at speeds above idle. A timed vacuum source is applied to the canister vapor tube, drawing fresh air into the canister through the air inlet located at the top of the canister. The fresh air flows through the tube to the bottom of the canister, forcing fuel vapors out through the purge line.
On high altitude models, the canister, Fig. 70, incorporates an integral purge valve. When engine is operating, manifold vacuum is applied to the purge valve through the top tube, while timed port vacuum from the TBI throttle body is applied to the purge valve through the lower tube. The manifold vacuum is used to lift the purge valve diaphragm, opening the valve, while the timed port vacuum from the TBI throttle body is used to control the rate of purge. During purge conditions, fresh air is drawn in through the air inlet at the top of the canister. The fresh air flows through the tube to the bottom of the canister, forcing fuel vapors out through the purge line.