Need help with vacuum lines on fuel tank

Fuel tank vacuum lines to where?
I had to rebuild a fuel tank and may not have put a hose in the right place, it has a stripe on it and and may go to sump tank ?
The car will
Hesitate and die when driving. I think it’s related.

The vacuum lines vary from year to year and one model (Coupe, Cabriolet, Convertible) to the next. I suggest that you put the year and model in your emails. I’d like to help, but I don’t have a clue if my car is similar to yours or not.


Paul M. Novak

1990 Series III V12 Vanden Plas

1990 XJ-S Classic Collection convertible

1987 XJ6 Vanden Plas

1984 XJ6 Vanden Plas

1969 E-Type FHC

1957 MK VIII Saloon

Ramona, CA USA

1989 xjs coupe 12 cylinder

Before I removed all the fuel hoses, fuel pump, filter and and sump tank from my '85 XJS V12, I added to these diagrams so I would know where everything went when I put it all back together. Do they help?


What I do is have various colors of finger nail polish and paint a dot of color on hose and near spigot .a

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Bravo, great diagrams. Very complete except for the Vac/vent lines which may be causing a problem. Can’t tell what MY your machine, but if the tank is not venting properly, you may be looking at a future oil-canning and ruptured seam experience. Drive the machine with the fuel tank cap. cracked or removed as a start to see if the thing runs with the system open to the outside. If good than suspect the venting system at the top of the tank on the Starbord side as you face it. This has been an olde issue over the years…if you look in the albums you might might locate my photo write-up on the vacuum/vent system and the notorious Rochester valve replacement. Best, JW

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I just saw that there is a mistake on my first diagram. Where it says “SUPPLY HOSE” , next to that in blue ink I wrote “FROM FUEL PUMP”. This is wrong. The supply hose comes from the fuel tank, not from the fuel pump. The fuel pump sucks from the Sump Tank.

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Thank you guys. It helps with the fuel but I do indeed need to see vacuum diagram. Does this exist? I tried to find someplace but to no avail. Thanks in advance,

Do these help? The bottom picture came from the Jaguar Factory Shop Manual, but is missing the explanation that came with it. Here is that explanation: “An evaporative emissions system is fitted to cars of US Federal and Australian design rule specifications. The system uses canister ‘A’ , containing active charcoal to retain fumes given off the engine crankcase assembly. ‘C’, and the fuel tank ‘H’, while the engine is at rest. When the engine is running, a stream of air is drawn through the air pipe ‘B’, by means of connections to the throttle edge tappings on the inlet manifold throttle bodies ‘D’, carrying absorbed fumes into the engine and purging the canister.”


These may help. I will take a look at it. I just know the hose has a stripe on it. Thanks so much

Brilliant, just what i need these pics to chexk wich hoses to clear on the vent system to charcoal canister.

The Jag-Lovers archives are a treasure trove of valuable information. I have observed over the past 24 years of Jag-Lovers membership that many “new” posts are about subjects covered many times before, sometimes decades ago. When I encounter an issue with one of my Jaguars I often spend time searching the archives for answers first before posting. In the vast majority of times I have found many helpful posts within minutes, often from several years ago like you did, that provide the answers or clues to solving my issue.


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Got under the car while oil changed and found rubber connector tube inside of the rear wheel, between two metal pipes. Mech blew some air back up into the tank and we smelt petrol a bit. Then the towards the canister. May have fixed it. Will see on some teat drives

That sounds like the vacuum valve CAC3101 or CBC6820 shown in the attached pictures. If that valve doesn’t work properly then vacuum can build up in your fuel tank.
There are lots of posts about this valve in the archives and in Kirby Palm’s book.


Paul thank you :pray:. Worked out what the pic is. Does your car have this valve and no rochester valve by the canister? This area on my car is just a rubber tube and no valve, maybe I should put one in? But need to find the cause of the blockage first

I think the problem may be rust particles from inside the condensor, getting in the pipe. Sometimes I have not had the probelm on drives. Jacking up tomorrow to have a good look up in this area and try blowing air both ways. Also wil try to get the condensor out and clean it.

Both our 1990 XJ-S convertible and our 1990 XJ-S convertible parts car had that vacuum valve at the front of the left rear wheel well as well as the Rochester valve connected to the carbon canister in the forward part of the left front wheel well. Both of these cars were North American market cars originally sold in the USA. Emissions equipment varied from year to year and from one market to another. It is entirely possible that your car, if it was a UK market car, was configured differently at the factory. Decals on the underside of the bonnet should provide the details of how your car was originally configured.


Attached is a picture of the carbon canister and associated parts from my 1990 XJ-S convertible parts car after I removed them from the car.

The Rochester valve is circled in red.
Our 1990 XJ-S convertible had the same setup. Cars sold in the UK market may or may not have been configured like this.


Great help thanks. Just to eatablish some facts, car is 1986 USA spec. I have no rochester vavle by charcoal canister, the vacum line into the B bank air maifold only has a vavle or switch (has electrical connectors) right between air manifold and cam cover in engine bay. No 2 psi one way valve in from left wheel well or under rear right well, just simple rubber tubes connecting small metal lines. After inspection my car only had one 2 psi one way valve immediately off the condenaor. This leads me to think after reading the K Palm notes, that my car possibly was pre recall and never had it done. What do others think, sounds about right??

After much fun and games wriggling around in the boot I found and removed the condensor. I did this by: removing the carpet cover over the ecu unit and relays. Unhook the relays and remove the 2 bolts holding on the ecu and move them to one side. This frees up space around the metal divider holding the ecu on. Remove the boot lid drain pipe and place behind the metal divider, do the same with the 3 (2 small 1 large) vent pipes from the tank to condensor. This gives acces and space for handa and tools to take the condensor off.

So I got the condensor out, 2 large bolts very annoying to get to using all the extesion and adaptors I had in my tool box. Testing the unit with blowing through the pipes, all were clear. Except the pipe coming off the condensor with the one way valve on it. This valve only allowed air BACK up into the condensor and not out towards the charcoal canister. Initially I though this vavle had been put in wrong way at some point, but the tubes where different sizes. As you can see from the pics the valve only allows air into the tank. The valve said ‘made in USA’ so obvious it was working fine… with the car in this set up I can’t see any way for the tank to vent, only allow air in during a vacume. Any other way it can vent???

I took a chance and turned the 2 psi vavle around with a bit of jiggery pokerry using a cut straw and gorilla tape. Replaced condesor unit and hooked pipes up for a test drive with the petrol cap fully closed and some hard driving in 2nd gear, through a tunnel… :ok_hand:

Result, very small wosh and no pressure build up in tank after driving. At the end of test run I could hear fuel pump whine from the boot. This was an intermittent fault that was pressent when i bought the car 2 years ago. I have NOT had this fuel pump whine while having tank pressue. No smell of petrol anywhere in boot or front wheel well afyer or during test drive

What do people think? Should the one way valve be this way around? My opinon is that it is prob pre recall system…

Going forward what will be the best set up for my car? I am thinking place 2 psi valve next to charcoal canister for easier access, or put in rocheater valve and vacume line before canister…

Thoughts apriciated…

P.s the people and help on this forum are amazing and I’m fully greatfull. Not all car clubs the same. I have had a super experience with Rover Coupe Club, and it seams similer here. So thank you all in advance…