How does the EVAP System detect a leak (big or small) in the system, what part is measuring the pressure? Where is the sensor?
Or is it detected another way?

Daniel

 

getting a check light for that system? Easy first thing to do is make sure the gas cap is on tightly, and or replace it.

 

The test is accomplished in different ways on different cars, but essentially a partial vacuum (not pressure) is drawn on the system and a sensor measures the rate at which the vacuum is lost. The leak rate, if unacceptable, is then classified as large, small, very small, etc.

Finding the leak can be very difficult due to the number of components located all over the car and the tubing that connects them plus the small volume of air that actually moves.

 

Thanks Mikey.
Where is that sensor, that detects the vacuum lost, located on the XK8?

Does it has anything to do with the circumstance that the fault-code (earlier large now only small leak) only appears when fuel tank is rather empty and often when I enter a tunnel/tube?

 

I would see if you can get a smoke test done on the system.

 

I'm not familiar with the specifics of the XK8 model. Fuel tank level is important- the system test is inhibited when the level is less than 1/4 or more than 3/4 approx. Can't imagine why a tunnel would set it off unless there's a momentary change in air pressure (?)

 

Before everything else check the electrical part of the system for issues. On a granddaughters Hyundai the search of their forum indicated that failure and CEL issues were more electrical than vacuum. Sure enough, connector removal and spray with WD40 and the issue went away.

 

There is a pressure sensor in the fuel tank.

What codes are you getting? The pressure sensor typically is not a problem in the EVAP system and sets its own fault codes when it fails.

 

Thanks for your answers.

The issue last since I got the car. its an american model which i brought to Europe. As I wrote in this forum this is a major problem on US-Cars, but it is unknown on european models !!!!

First I had always the big Leak message: P0445 and since a few months only the small leak: P0442
I just clean the code with obd-2 readers when it appears.

I changed some of the rubber hoses which were broken and O-rings on Canisters.
Smoke test ist unknown here they don't have the equipment !

Now I bought a Smoke-Can which is used in Discos for Showeffects. I will try to find the leak with this "ordinary" procedure.