I am trying to find info about the purge valve that is connected to the engine breather pipe. What the heck does it do? Is there a testing procedure to determine if it is even working? It looks like it aids in ventilating the crankcase? The two wires coming off of it get lost into the wiring harness, so I am not sure where it's power comes from.

 

Jaguar was very tight-lipped about this

The valve opens so that vapors in the vapor canister can be pulled into the engine and burned. Operation is controlled by the thermo switch (at the very rear of the water rail).

There might also be a tie-in with the 'air switching module' (RH inner fender near the diagonal fender brace) but the exact functioning of that device has never been 100% clear to me and I've never seen it explained in any Jaguar service literature

Anyhow, from memory, that thermo switch is normally closed and then opens at something like 157ºF. If my assumptions and memory are correct then the purge valve is operating (opened, and allowing vapors into the inlet system) only when the engine is below 157ºF

Cheers
DD

 

it is just a purge valve similar to the ones used by Ford. In fact Ford still uses the same identical purge valves. There are two different types: one has a plug-in connector, the other has two wires, just like the one in the XJ-6.

to test the valve, remove it from the hoses, find a pair of long wires, connect them to the two wires at the valve, connect the Ground to the battery Negative pole, and then touch the other wire to the positive pole, the valve should click open as you touch the positive pole and close when you stop touching it. You can feel the valve operating as you hold it in your hand.

This valve was installed by Jaguar dealers, some kind of recall they had after 1980, it was done to try and resolve the vapor buildup in the tanks which caused the tanks to expand to the point of breakage, a fix which of didn't work, because the problem was the plastic GM check valve before the canister which some XJ still have today.

go to eBay and type "Ford Purge Valve" in the search box and you will see it.

 

Hi Folks,

I'm hijacking this old thread because it's so close to what I need to ask.

I took out this purge valve two years ago because it didn't seem to hold vacuum. I just replaced it with a hose. This was fine, but now I have to put it back for a California smog check. So...

Which wire goes to which?

The switch has red and white wires, the harness has black and white wires.

Grateful for the help, as always.

-mB

 

if for the 1985 XJ-6, try this:

black is ground, white is hot

white is ground, red is hot.

but it doesn't matter, they never work anyway, the purge valve is a domestic universal purge valve used by Ford, GM, you name it, the difference is in the connectors.

to test it, connect one wire to the battery ground post, and touch the other to the positive post, you should "feel" the valve click open-close.

 

I get it, sorta. It is a part of the gas tank vent system. In modern cars, the fueling system is closed from the atmosphere. In the old days, the fuel tank vented to the atmosphere. Another term might be "tank vacuum avoidance system".


At one time gas caps came as vented or unvented. Mixing could cause a tank collapse.


The system in out Jaguars is the same or similar to the method used by GM. I've compared the GM carbon canister in my bits bin to the one residing behind the right out board lamp on my S3.


And, when the DOHC 6 departed, I used the same hose from the canister to connect it to the LT1 purge. Works just fine. I think.


Now, CA SMOG tests include a tank evap test. The ability to retain attest vacuum.
The last time around my 94 Jeep flunked that one. Leaking cap. Plastic thing had a crack!!! Replaced with a generic of the Stant brand, and all is well.


Carl

 

Thanks to Jose for the wiring color code. I had it wrong, of course, thinking that the white would connect to white. Silly me.

I don't really care if it works. I can't believe that having even a working purge vale in there is as good for air quality as the piece of hose I was using. But I'm not going to try and explain that to a smog check technician.

As far as the evap test, in Colorado at least that part has always been marked "n/a" because they don't have a way to test the wonderful art deco sculptures that are the gas caps on my XJ6 and XJS. Which is okay by me. It's also on the CA state website that the evap test does not apply to "Vehicles with two or more fully operational fuel tanks". Suddenly I'm grateful for that added complexity.

-mB

 

you welcome Mike,

the car should pass inspection with or without the purge valve, even without catalitycs, as mine passes without them.

what you need to make sure of, is to drive the car for at least 1 full hour before you take it to the station. The cooling system thermostat needs to go through its cycles of open and close and stabilize.

The colder the outside temp, the more you should drive it before testing, and the better the chances of it passing when fully warmed up.

 

Passing the tailpipe test is one thing. Passing the visual inspection, if one is made, can be a different story ! Some areas want to see all the equipment in place. Even if your car runs clean you could fail due to missing equipment. Silly.



Cheers
DD

 

Yeah, here in CA, the visual is an essential part of the test.


Mike:


Thanks. I wondered how my tanks ever passed. They would likely not, were there not an exemption !!! So, I guess I am purging some atmosphere!!!!


Carl

 

what can be done is to open up one end of the front cat, the bottom cap
usually starts to separate anyway, remove the honeycomb guts inside, weld it back, pressure test it, and reinstall it. Passes the visual fine. And you need it for the O2 Sensor mount. Engine runs better. I removed both my cats; The second Y cat, I replaced it with the European catless Y pipe. wonderful improvement, and no more hot spot under the driver's floor. I also sent the pipes to Jet-Hot Coatings for their ceramic-silver "Sterling" coating inside and out, another improvement over improving the entire exhaust system.