RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Fig. 5 LDP At Rest
LDP At Rest (not Powered)
When the LDP is at rest (no electrical/vacuum) the diaphragm is allowed to drop down if the internal (EVAP system) pressure is not greater than
the return spring. The LDP solenoid blocks the engine vacuum port and opens the atmospheric pressure port connected through the EVAP system
air filter. The vent valve is held open by the diaphragm. This allows the canister to see atmospheric pressure.
Fig. 6 Diaphragm Upward Movement
Diaphragm Upward Movement
When the PCM energizes the LDP solenoid, the solenoid blocks the atmospheric port leading through the EVAP air filter and at the same time
opens the engine vacuum port to the pump cavity above the diaphragm. The diaphragm moves upward when vacuum above the diaphragm exceeds