Grand Cherokee 2WD Limited V8-4.7L (2002)
Fig. 13 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. 14 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 spring
force. This upward movement closes the vent valve. It also causes low pressure below the diaphragm, unseating the inlet check valve and allowing air
in from the EVAP air filter. When the diaphragm completes its upward movement, the LDP reed switch turns from closed to open.
