Hello folks! New here. Question: Is this Rochester tank vent control valve mounted on the engine compartment side of the front fender, driver’s (LHD) side, or under the wheel liner on the wheel side of the fender? I have read conflicting accounts. I have the classic pressure and vacuum problem with my new to me 95 XJS, convertible, triple black, wire, 6Cyl FI Auto. Need to find and source a new valve, apparently this is what resolves the issue, as long as the lines are not clogged, which I will check once I positively locate the position of the Rochester valve. Thanks! Pete
Jack up the drivers side front wheel.
Remove it.
There is a trap door facing the front of that wheel well. Remove that. That’s where it’s at. Bring a philips head screwdriver and remove the front wheel well completely for better access.
BTW, the rear facing side of that same wheel well has the fuel filter…
Fantastic, thank you.
Hi. And welcome to the ownership of a fantastic car in the 4 litre Celebration. I had the same problem and after finding the valve and cleaning it and the pipe work I found that the problem was that someone, not me, had omitted to plug the top end of the pipe back into the vacuum nipple on the top of the engine. It’s a devil to push on but it works and no horrible wooshing sounds at the filler pipe ever since. Good idea to check that first. There are two similar pipes on the top of the engine. Needless to say they should both be plugged in and not hanging diseptively down the back of the engine. If you do decide to to remove and clean the valve it does split apart top from bottom and clip back together again. It really doesnt look like its supposed to but it does. Be careful though. Inside there is a spring and a rubber diaphragm which come out. You want to see how they are positioned before the fly across your garage in different directions. Good luck. Richard.
Thank you very much! I will check this. I still don’t really see the full schematic for this system… My antique Fiat Spider has a similar system, but the intake on that car is constantly drawing a metered amount of air back through the canister into the intake when the engine is running. The O2 sensor makes needed minor adjustments, so there is no funky valve system to fail. Make up air for the tank goes back through the canister top and into the gas tank. Simple and it works. This one, I still need to understand more fully. I think that this Rochester valve controls airflow in both directions? Make up air for the tank, plus expansion release for the tank?
Pete Lenk
Not sure exactly where I should be looking for this? Vacuum nipple on top of the engine?
Hi Veekay.
If you are looking at the engine from the near side there are 2 what I call vacuum nipples protruding from the flat hatched manifold casting between the first and second inlet manifold. There’s a a black rubber pipe with a white stripe running up from the alternator area of the block. This almost disappeared under the left end of the fuel rail but you can just see where it ends. To the left of it is another short black and white pipe which comes out of the nearby Lucy’s pressure regulator. The first pipe is from the Rochester valve. Mine was just hanging loosely in the gap between the first and second manifold and the block! Make sure it’s plugged in. My photos should show you where the pipe comes from and my fat chubby finger is resting against the other end where it is plugged in. One shot is from the offside looking over the valve cover. Hope this helps. Cheers. Richard.
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Super helpful! Thanks for taking the time to post these pics!
My pleasure. Not the easiest thing to photograph clearly but you get the idea. By the way I don’t really give bits of my car names!! Lucy is of course meant to be Lucas but predictive texting wasn’t having any of it!! Cheers. Richard.
Superblue always makes that sound (and a major “fart” 
) when I remove her fuel cap if her fuel level is VERY low. I was thinking that was the norm in that situation, esp. in hot weather (?) 
For some reason that seems backwards to me, VK, but then I have been a bit confused of late on a lot of things … 
I have removed my Rochester Valve and have done some tests and it is clearly the source of the fuel tank pressure/vacuum, problem. I would like to replace it, but I am having the devil of a time finding a source. Anyone know where this or an equivalent is sold? I assume a pretty common alternative must be available.
I don’t yet know how to upload a photograph, I am new here, but will see if I can figure that out.
Car is '95 XJS, 6Cyl.
Rochester Purge Valve is marked : 17089101
2 large hose connections on either side, small vacuum hose connection out the top. Circular shaped .part
Same as in the 6.0L V12. Try searching for GM PART number 17089068 or AC/Delco 214-552
Thank you! Yep, mine is marked exactly that. I will source one of the 2 you suggested.
Update: just ordered one, should be here on the 10th.
Next I need to get the canister out and see what is up with it. Now, for the life of me I don’t understand why there is a second valve, with a solenoid on it. The purge valve should do everything necessary to guide both fumes and fresh air each way through the canister?
If it is to “slow down” the flow, or meter it, that can easily be done by just throttling down the fresh air intake hole size. The flow will be constant (or vary only with engine vacuum) and the O2 sensor will make any minor needed adjustments. Not sure why that solenoid valve is even in the system?
Pete
p.s. I figured out “edits”, but how does one post photographs here? I don’t see a button for it.
You can’t apply a vacuum to the canister. That would apply a vacuum to the tank and it would collapse.
The arrangement of purge valves - two vacuum operated valves on the V12 - is to purge fumes from the canister at a controlled rate. Too fast and the engine runs rich and flunks emission tests.
But a vacuum is applied constantly by the intake to pull air through the canister, collect fumes and burn them? There is a large open hole on the top of the canister. Or does this vacuum purge valve shut off that flow through it when the engine is running and then allow the solenoid valve to take over, with CPU and O2 sensor control? That would make sense, and provide the rate control that you mention is necessary to keep the mix near stoichiometric.
I get that about the solenoid controlled purge valve, (on my 6 cylinder, this is a second control valve, mounted at the side of the canister up front) regarding regulating the rate of return of fumes to the intake manifold. I would assume that the O2 sensor sends data to the CPU and it turns that solenoid valve on and off.
I wonder if anyone has an operational schematic for this hydrocarbon control system, or can point to where one might be found? It does seem somewhat overly complex, but when these work, they are well worth it and quite beneficial to the environment.
Out in CA, I remember reading somewhere many years ago, that the percentage of smog that was caused by unburnt hydrocarbons was shockingly high, well into the double digits, but I don’t remember the exact number. I am totally on board with restoring this system on my '95 XJS.
One possibility as to why this has failed on my car is that the mounting bracket for the canister and solenoid controlled valve is so perished by rust that the valve may have lost its ground connection and is not responding? It is pretty bad under there up front. I am going to cut this all out and fashion a new mount for both these components.
Thanks for your help, much appreciated! Pete
Little bitty vacuum hose and great big vent opening means no vacuum, just airflow.
From the manual for the 6.0L V12, but should be very close to what you have on the 6-banger, minus the plumbing for the second bank
Perfect! Exactly explains it. Thank you. It makes sense, if a little complicated, but everything on these lovely British cars is complicated. I have ordered a new Pressure Control Valve, but in the interim, I sprayed the innards of it with WD40, soaked it well, and purged it with compressed air, then tested the vacuum side with my vacuum pump, and it now appears to be working. Popped it back in place, and viola! No more wheezing when the tank cap is opened. Given that there is no wheezing, the displaced air is obviously getting through the canister to atmosphere, assuming no leaks along the way, which I believe to be true. It is questionable how efficient, or even, the flow is through the canister after these 27 years, but I will pull it out and give it a good inspection. Plus the bracket that holds it all in is so incredibly badly rusted that it must be replaced. I need to find a good US source for general used parts, preferably somewhere in New England that I can drive to, but that might be too much to ask. Thank you for your help, this has answered all of my questions! My Check Engine light has been reset and is staying off now, so I can get that first Inspection Sticker that I have been needing.