Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
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.