Evaporative Emissions System: Description and Operation

Fuel Filter And Lines.:

PURPOSE
The evaporative emission control system limits fuel vapor escape into the atmosphere. The system (EECS) transfers vapor from a sealed fuel tank, through a single vapor pipe to an activated carbon (charcoal) storage device (vapor canister) to store the vapors when the vehicle is not operating. When the engine is running with coolant temperature above 70°C (158°F), vehicle speed above one mile per hour and more than four percent TPS, fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.


CANISTER PURGE CONTROL
The PCM controls the canister purge system by energizing and de-energizing the canister purge solenoid by supplying a ground for the solenoid. When the solenoid is energized, fuel vapors are drawn, by manifold vacuum, into the intake manifold where they are burned in the combustion process.


VAPOR CONTROL
Fuel vapors from the fuel tank are purged and flow into the vapor canister tube labeled fuel tank and are absorbed by the carbon. The canister is purged when the engine is running above idle speed. A timed vacuum source is applied to the vapor canister tube labeled canister purge to draw fresh air through the air inlet, at the top of the canister. This air flows through a tube to the bottom of the canister and forces the vapors out the purge line.

NOTE: The 1992 vehicle canister has a vent cap or short piece of hose to direct vapors. 1991 vehicles have a vent line routed into the right hand frame rail.