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

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

1986-87 V6-173 & 1987 4-151 Engine
The canister , Fig. 66, is purged whenever the engine is operating at speeds above idle. A timed vacuum signal is applied to the canister purge tube, drawing fresh air through the bottom of the canister. The fresh air drawn through the bottom of the canister, mixes with the fuel vapors in the canister. This mixture of fresh air and fuel vapor is drawn into the intake manifold to be consumed during the combustion process.
The system used on 1987 V6-173 engines, also incorporates a thermostatic vacuum switch, which is mounted on the intake manifold, to sense coolant temperature, Fig. 67. This two port switch is connected between the TBI unit and the canister. At temperatures below 115°F, the thermostatic vacuum switch will be closed, preventing canister purge. At temperatures above, 115°F, the switch will open and allow purging of the canister.