Evaporation (evap) canister. Duty cycle evap canister purge solenoid

Evaporation (evap) canister

DESCRIPTION

A maintenance free, EVAP canister is used on all vehicles. The EVAP canister is located under the vehicle, inside the left frame rail, in front of the fuel tank (Fig. 2).

Fig. 2 EVAP Canister Location

1 - LEFT FRAME RAIL

2 - RUBBER GROMMETS (2)

3 - LOCATING PINS (2)

4 - EVAP CANISTER

5 - MOUNTING NUT

6 - MOUNTING BRACKET

OPERATION

The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister.

Fuel vapors are temporarily held in the canister until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canister to be purged at predetermined times and at certain engine operating conditions.

Duty cycle evap canister purge solenoid

OPERATION

The duty cycle EVAP canister purge solenoid (DCP) regulates the rate of vapor flow from the EVAP canister to the intake manifold. The Powertrain Control Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid.

When de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During closed loop operation, the PCM cycles (energizes and de-energizes) the solenoid 5 or 10 times per second, depending upon operating conditions.

The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time that the solenoid is energized. The PCM adjusts solenoid pulse width based on engine operating condition.