Hello Jag-lovers! Got a XJS V12 -89. And a little problem. My car is one of those that supposed to have been recalled for the installation of the rochester valve in the evap system. According to Jaguar this was done to prevent “excessive fuel vapor pressure”. Which is exactly what I have in my tank now. And this mod is not done on my car. So, since the parts is difficult to find and the rochester valve seems to be not that reliable according to forum users I intend to install the solution suggested by Kirby. That is, a solenoid valve and a 2psi vavle for when the engine is not running. However, I have difficulties to find those parts. Maybe because I am from Sweden and dont know the proper terms to search for. Can anyone provide me with a few links to where to by those? Maybe someone have done it on their car and have a specifik suggestion?
Thanks!
You should already have a 2 psi valve. That’s what got replaced with the Rochester valve in the recall. Where it is, though, might be a puzzle. With any luck, it’s near the carbon canister – but it also might be near the vapor separator up in the RH flying buttress. It must be in the line between the vapor separator and the carbon canister, but that’s a long line and can take some searching.
When you find it, check to see that it works. Removed from the line, you should be able to blow through it with your mouth with so little effort it almost feels like an open passage. If it’s plugged in either direction it needs to be fixed or replaced.
You need a solenoid vacuum valve kinda like this one:
There may be a couple on your car already. There was one added to the cruise control via a recall, but it doesn’t sound like recalls were performed on your car. There’s also usually one or two in the vacuum advance plumbing, but you may have the later Marelli ignition that doesn’t have any vacuum advance plumbing.
These things have three ports: One common, one normally open, one normally shut. One port in the photo has an air filter on it, that’s the black cylindrical thing at the left end. On some versions, you can move that around to different ports.
For your purposes, you want to tee into that line between the vapor separator and the carbon canister on both sides of the 2 psi valve. Connect a line from one tee to the common connection on the solenoid valve, and connect a line from the other tee to the normally closed connection. You’ll want to cap the normally open connection. Then connect a switched 12V to the coil, so that it’s energized whenever the ignition is on.
I also recommend a pair of inline fuel filters, one in the line between all this valving and the carbon canister and the other between all this valving and the vapor separator. This is just to keep dirt out of the valves.
Hello and thank you for the quick response!
Yes I know I have the 2psi already, but I think I will throw it away and install a new one when I am at it anyway. At the same time I can install the new one near the canister since it will make things easier connecting the solenoid for the bypass.
Will also follow your recommendation with the inline fuel filters. I like to do things thorough once rather than have to go back over and over… 
Thank you again for your suggestions, I will look it up right away!
/Magnus
Hello again Kirbert, a small update and another question. The recall-documents specified the location of the 2psi to above the rear axle underneath the car on the left side, and there it was. I have removed it and tested it, it was stuck as expected. I have fixed it and will reinstall it more conveniently near the canister. And install a solenoid valve to bypass it when the engine is running. My question is, you write here that I need a solenoid vacuum valve but in your document you talk about just a solenoid valve. As I understand it I don’t really need a vacuum solenoid, just a solenoid valve with two connections? Or are there some benefits with a vacuum one, easier to find maybe? I’m just checking if my understanding of it is right.
(the vacuum solenoid for the cruise control was actually installed)
Magnus,
You could use either a solenoid valve or a vacuum valve.
The idea is that when you start the car you are sure that the tank is free to vent and not depending only on the Rochester valve.
Thank you! Got it
Den lör 28 nov. 2020 18:23Aristides Balanos - 1986 XJ V12 VDP SIII via Jag-lovers Forums <noreply@jag-lovers.com> skrev:
Semantics. I’m suggesting the use of a solenoid valve as customarily used to control vacuum. Doesn’t really matter, I guess, any type valve that can be connected into a 1/4" vent line and controlled to be open when the engine is running and closed when it is not will do.
Yes I guessed so, unfortunately I’m a sucker for semantics
I’d like to take the opportunity to thank you for the obviously extensive work with the help-document for the XJS. Invaluable. Great work!