I have an 04 XJR. I am getting a faint tapping noise from the drivers side firewall area heard inside the car.The tapping is rythmic and does not change with engine RPM.

Any Thoughts?

 

Sounds like your purge valve. Was a common issue on 04 XJ. If you replace it, the noise should disappear. Bear in mind I am not there to hear it. So best guess only.

 

Good call on the purge valve. I have isolated it as the suspect component. Does the ECM send a pulsed output to the valve? It was my undersatnding that the valve remains in a fixed state once the car is running and is between 1/4 tank an full.Wondering why a tapping noise if the signal is fixed. The ECM is not setting and DTC codes, so I assume that vaccum is being held in the canister. There was an issue with the vent valve earlier this year which was setting a gross evap leak code. It was still under warranty and the dealer took 4 trys to get it right. Replaced gas tank filler neck, gas cap, and two reset visits..... 5 days in the shop for a vent valve

 

It is a pulse width modulated signal sent to the purge valve. If it was stuck open all the time, the car would likely run rough and smell of fuel. The ECM only wants to allow metered amounts of fuel vapor into the engine to be burned off.
The PWM is why it ticks like that.
Glad you found it.

 

can somebody please show me a diagram, or describe where this purge valve is and possibly a part number for the 2005 super v8? I have the shop manual cd but cant nail it down. they describe one where you have to pull apart half the car to get to... don't know if this is it?
thanks!

 

bump

 

domer94;

Take a look in the Factory Manual 04-09, Section 303-13 (pg 3335 of 6384). I've not worked on this myself but the manual suggested referencing the section on the throttle body first. I wonder if this implies having to remove the throttle body to get to it. Search the forum for the Workshop Manual download instructions if you do not have a copy.

Best Regards, william