Description & Operation
The leak detection pump is a device used to detect a leak in the evaporative system. The pump contains a 3-port solenoid, a pump that contains a switch, a spring-loaded canister vent valve seal, 2 check valves and a spring/diaphragm.
Immediately after a cold start, when the engine temperature is between 40F and 86F, the 3-port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non-test test conditions, the vent seal is held open by the pump diaphragm assembly, which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling. This is due to the operation of the 3-port solenoid, which prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized, allowing atmospheric pressure to enter the pump cavity. This permits the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de-energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:Pump Mode
The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test time.Test Mode
The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the switch closure point. The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5 inches of water.
When the pump starts, the cycle rate is quite high. As the system becomes pressurized, pump rate drops. If there is no leak, the pump will quit. If there is a leak, the test is terminated at the end of the test mode. If there is no leak, the purge monitor is run. If the cycle rate increases due to the flow through the purge system, the test is passed and the diagnostic is complete. The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.
Removal & Installation
- Properly release the fuel pressure.
- Remove the air cleaner lid; disconnect the inlet air temperature sensor and makeup air hose.
- Remove the negative battery cable.
- Raise vehicle and support.
- Drain fuel tank.
- Remove fuel tank and EVAP system.
- Remove the 3 mounting screws.
- Remove LDP from bracket.
- Remove hoses from EVAP canister.
- Disconnect electrical connector for Leak Detection Pump (LDP).
- Connect electrical connector to the Leak Detection Pump (LDP)
- Install hoses and lines.
- Install LDP onto bracket and tighten to 3.9 Nm (35 inch lbs.)
- Install the fuel tank and EVAP system.
- Lower vehicle.
- Install the negative battery cable.
- Install the air cleaner lid, connect the inlet air temperature sensor and makeup air hose.
Fill fuel tank. Use the scan tool to pressurize the fuel system. Check for leaks.