Jeep Wrangler/YJ 1987-1995 Repair Guide

Evaporative Canister


The evaporative emission control system prevents the release of unburned hydrocarbons, present in gasoline or gasoline vapor, into the atmosphere. When pressure in the fuel tank is below 3 psi (21 kPa), the pressure relief/rollover valves open allowing fuel vapors to flow to the evaporative canister where they are absorbed by a charcoal mixture. This prevents excessive pressure build-up in the fuel system. Most canisters are equipped with a calibrated orifice at the inlet to the canister.

The evaporative canister is mounted to the passenger side frame rail. Inlet ports on the canister are connected to the rollover/pressure relief valves, the air cleaner, and the fuel tank vent through hoses and tubes.

Canister purge operation is activated by the purge shutoff switch. An air cleaner venturi provides the vacuum to open the switch which allows vapors collected in the canister to be drawn into the airstream. The vapors then pass through the intake manifold and are burned in the combustion process.