I see the purge valve solenoid but I do not see the LDP.
Is it hid some where?

Please help

Ric

 

Im not sure if its what youre referring to but theres a purge canister thing under the truck above the rear axle bolted to the floorboards. I think 97 was the first year it was located there.

 

It is a 1998 XJ, Purge Solenoid is found on the firewall on the right side.
The problem is I do not find the Leak Detection Pump.

 

What makes you think you have an LDP?

 

Could it be I don't even have one?
Maybe I'm looking for a Leak Detection Pump that is not here?

 

What would it do?........pump away whatever is leaking?

 

There's supposed to be an emisson compliance label on the firewall, above the brake booster. It should say if the Jeep meets California or Federal emissions standards, and show a diagram of the emissions system. If you have a California Heep the placard should show an LPD in the system.

Look for it.

 

How about diagrams?

EPA emissions vehicle (no LDP):





CA emissions vehicle (with LDP):




Those are from the FSM for the 2000, so it may not be exact.

 

What, and where too, does it pump?

 

I thank all of you for your information. I know that I don't have a LDP.
Thanks all

 

Clear as mud:

LEAK DETECTION PUMP (LDP) OPERATION

The Leak Detection Pump (LDP) is used only with certain emission packages.
The LDP 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, engine temperature between 40°F and 86°F, 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.

 

If I'm reading that correctly, the short version is that the LDP pumps air into the system, and the LDP monitor checks the pressure to see if there is a leak. If the system loses pressure, the test fails. The computer then records the failure. I don't know if that results in a CEL or just a failed emissions item. It's basically checking to make sure that the evaporative system is pressurized, whereas on EPA vehicles nobody cares.

 

Here's the DTC's that will be stored:


P0456-EVAP LEAK MONITOR SMALL LEAK DETECTED (.020)

Edit: A few more LDP related DTC's:

P1486-EVAP LEAK MONITOR PINCHED HOSE FOUND
P1494-LEAK DETECTION PUMP SW OR MECHANICAL FAULT
P1495-LEAK DETECTION PUMP SOLENOID CIRCUIT

 

Will those light up the CEL on the dash, or just show as a failed emissions item in the emissions readiness check on a scan tool?

 

CEL. Any emissions related DTC wll illuminate the CEL.