I have read a bunch of threads that discuss the purge valve, how to replace it, etc.. but I have no clear understanding exactly of why it ticks.

Can anyone explain?

Recently I got a P0456. Now I just started getting this noticeable ticking. No fuel smell anywhere.

Before I start taking it apart it would be nice to know why the ticking occurs at all.

 

The purge valve releases stored fuel vapor from the charcoal canisters into the intake. The release is controlled by the ECM based on engine running requirments, vacuum and fuel tank pressure. Control is achived by modulating the purge valve (basically a high speed solenoid operated air valve) at about 100 Hz at varying open times (pulse widths). This modulation is the ticking that is audible.

 

Based on that it seems that the ticking is by design. So why haven't I always heard it? What makes the ticking start becoming noticeable?

 

Temperature, condition of the internal diaphram, internal corrosion and the condition of the rubber isolation mounts are all factors in how audible it is.

 

On my 05 VDP I have never heard such a sound and it has twice the mileage on it.

What is so different about the two systems that would make the XK8 such a noise maker?

 

There is a known issue with the one with your 2004. I have attached the TSB. They also add sound insulation. Unfortunately this new valve needs an ECM reflash also.

There were also different problems with the valve in earlier years described in other TSBs.

I have no answer why Jaguar screwed this up repeatedly.

 

Thanks for the TSB. Now its getting interesting.

My VIN is 38840 is past the range that the TSB lists to require the ECM reflash.

From what I read it does not seem that the ticking is a real problem, more of a nuisance.

So no rush to fix it? I could order a valve and continue to drive the car until I can install it?

I guess there is nothing serviceable in the valve?

I wonder did the P0456 cause the valve ticking or did the valve cause the code?

 

I should have looked up the code earlier. According to JTIS, it probably is not a purge valve issue, so the noise could be the system inhibiting the purge valve to compensate for another problem.

The small evap. leak is not something that should prevent you from driving the car until it is repaired. It will likely prevent you from passing a state emissions inspection however.

A new fuel cap would be an inexpensive, logical place to start.

 

I guess maybe I was looking too hard for a bigger problem.

I checked the gas cap and it was tight but the seal was a little wet with fuel. There was some buildup on the filler tube inlet face so I cleaned that up and cleaned the cap.

Cleared the code and so far it has not returned after a 30 minute drive.