LDP-Purge System Integration

• The function of the LDP is to pressurize the fuel tank and the evaporative emission system (approx. 25mb.) for the purpose of detecting leaks.
• The canister vent valve is integrated into the LDP which is electrically controlled by the ECM. The canister vent valve is sprung open to provide fresh air entry into the fuel system during purge operation.
• Purge operation characteristics are:

Off Idle through Full Throttle:  Purge Valve(s) opened by pulse width modulated control of the ECM(s). Duty cycle varied by engine operating conditions.

Warm Idle:  Purge valve(s) open slightly

Cold Idle/Decel:  Engine temp > 67°C, Purge valve(s) closed.

Fig 1: Identifying LDP-PURGE System Integration

• During diagnostic testing of the evaporative emission system, the vent valve is closed and will block atmospheric venting. The purge valves are also sprung closed to seal the system.