How is the fuel system setup. The extent of my knowledge on it is that it goes to the rail, through the cooler and then back to the tank.

I drove my car around town way more than I usually do and started to smell gas today. Upon inspection I can't find any leaks, and cannot pinpoint the smell. I pop the gas cap and let out a good bit of pressure.

Is this a closed system or should something be relieving the pressure? Maybe it is relieving the pressure and I am smelling the fumes?

just a bit confused

 

SS
Read the Great Palm's book on the fuel vapour recovery system. It is almost certain that the whoosh you are getting is air rushing IN to the tank as the fuel used is partially evacuating it.

USA spec cars have a complex vapour cannister system that you will need to go carefully though to fix the problem.

In your car fuel is circulating all the time, with the "upstream" pressured side being between the pump and the B bank (US driver's side) fuel pressure regulator. So the rail is always under pressure. Downstream of the B bank regulator the fuel goes back to the tank. Lines run under the car: pressure side exits the boot front bottom RH corner as you look into the boot, the line goes over the cage top and along the US passenger side floor then into the engine bay though the firewall.

The return line to the tank is the mirror image but goes back down the US driver's side floorpan and into the boot LHS front corner.

Fuel smells are a real problem in the XJS and can only be 100% cured, in my experience anyway, by addressing tank floor pinholes, renewing the uner-tank rubber mat, renewing all the flexibles in the system, and having the filler tube gasket and flexible hose renewed. There are flexibles in the pipe that carries fuel over the rear cage, and these, and the metal tube, are quite exposed to road grime etc etc, and they rust out and fail.

Nice spring project for you! good luck

Greg

Greg

 

In any Jaguar I've owned I'd have to answer your question as "not very good" Your tank shouldn't "whoosh" it's going to try and task your welds as it tries to implode. On both my XJ6 Series III and my current XJS I drilled a small hole in the cap to allow venting to take place the Rochester valves by the canister fail and truley the whole system is far more complex then it needs to be. Even the line from the tank forward to the canister is too small with too many intricate bends to be effective.

 

anyone have ideas on the gas smell? I don't want a fire but I can't find the source of the smell or any leaks

 

Vent your tank so it doesn't "whoosh" then drive the car and see if the smell subsides...worked for me.

 

The air is definitely coming out. Driving around in florida I think it is just the gases expanding inside the tank

 

worth a shot, i probably need a new cap anyway as the seal is still original. Obviously it seals if it is holding in air/vapor. Any downsides? There wouldn't be any weather intrusion since its just a hole and there is a seal door over top the cap.

 

What size hole(drill bit) did you use/drill? Not really sure if this is the way anyone should go.

 

If "anyone" wants to trust the archaic Jaguar vapor recovery system then be my guest. Most Fed Spec cars got the complex charcoal recovery systems where some non-fed spec cars did not (or lesser). Most cars as old as ours the charcoal can has long out lived it's usefulness and most didn't work right to begin with. It's sole purpose is to not let fuel vapors vent to the atmosphere, once the fuel heats up in the tank and low PSI valve is supposed to open letting the vapors into the can then on start up the solinoid valve is supposed to open and allow the stored vapors to be burned...yeah right and in about 10 minuets a monkeys going to fly out of my a_ _...well you get the picture. When the fuel is being used by the car the the system is supposed to allow the tank not to become a vacuum "whoosh" anyone! My 87 XJ6 had both tanks implode (common problem) due to me trusting Jaguars ancient faulty system...no thanks, I'll vent it the old school way with a small hole in the lid. My Tr-6, edger, lawn mower etc vent in this fashion as well as every time I fill up my car their is no "vapor" recovery system here in Florida. My Z4, Mercury, Pontiac and XJ6L have better more modern systems that are monitored by the ECU and will throw a code when the tank vapor/vent system is not operating properly (still won't effect drivability) and lets me know my tank may be in danger (whoosh anyone!) my XJS tank will simply implode or if it can't vent when sitting in the heat will perform the opposite both of which will task the integrity of the tank and cause the seams to sweat/leak. The rochester (low psi) valves are no longer available to my knowledge.

 

I took the metal back plate off the cap and drilled a 1/8th" hole in it and then a 1/8th" hole in the plastic lid offset from the plates hole. I took the line from the tank to the canister off at the canister and installed a small engine fuel filter on it to prevent critters from crawling in it and left it off the canister then plugged the engine vacuum at the canister. My valve barely opened up when tested at a high psi and only some of the times I tested it plus the line back to the tank seemed restricted. My fuel smells in the boot went away after doing this plus I also had no visible leak signs anywhere in the boot or around the tank. Put a gas can half full of gas in the driveway with the lid on and the vent plugged, the can will swell up in no time. If your rochester valve are not working and your line is restricted (it's restricted by design, trust me) your tank will do the same thing when sitting in the heat (woosh anyone!)

Copied from JAG-LOVERS>>>
Vapor Recovery System

The carbon canister vent is an excellent system, does not hurt the performance one iota (as opposed to some other emission control systems) and is normally maintenance-free.
Overview

When the car is running and drawing fuel out of the tank, there must be a vent system to allow air into the tank to prevent a vacuum from being created. It is no longer acceptable to merely have a small hole in the gas cap; such methods allow fuel vapor to escape into the atmosphere all the time, whether the car is running or not, and would contribute to air pollution. Now, unless you live in California where they have intelligently-designed gasoline pumps, you pump 20 gallons of fuel vapor out into the air every time you pump 20 gallons of liquid gasoline into your car, and proper fuel tank venting begins to look like an inconsequential issue. But we will endeavor not to get into a discussion of the real intentions of our legislative bodies.
Nowadays, the vent system from a fuel tank is connected to a carbon canister. When vapors from the fuel tank try to escape through the canister, they are absorbed by the activated charcoal.
Of course, the charcoal can only absorb so much fuel. Therefore, whenever the engine is running, there is a system by which the engine draws fresh air through the canister. This draws the vapors back out of the charcoal and burns them in the engine.
Breathing

When the car is not run for extended periods of time, the amount of vapor generated in the tank could be considerable. Gradual changes in ambient temperature and barometric pressure would cause the vent system to "breathe", running a large amount of vapors through the canister. To absorb all this vapor, the canister would have to be prohibitively large.
To prevent this, there is a valve in the vent line between the fuel tank and the canister. This valve will allow air to flow in either direction, but only after a certain pressure or vacuum has been reached. If the contents of the tank expand and try to escape out the vent, it will prevent any flow until the pressure reaches a set value, and then it will allow it to pass to prevent damage to the tank or hoses. Similarly, if the contents of the tank contract and try to draw air in through the vent, the valve will prevent any flow until the vacuum reaches a set value, and then it will allow it to pass to prevent the tank from collapsing. As a result, the vast majority of the smaller expansions and contractions do not open the valve at all, and the amount of vapor the canister is expected to absorb is greatly reduced.
Of course, this means that at any given time the fuel tank and hoses may be slightly pressurized, even when the car is not running. Even the tiniest leak anywhere in the system may become quite significant.
Recall Modifications

The original XJ-S vent system pretty simply followed the description above. However, there were indications it did not work as well as intended (including numerous complaints about fuel odors), so there was a recall to address the system. As a result of the recall, there are components of the system that are positively operated by engine vacuum; in other words, valves that are opened when the engine is running.
Canister Replacement

Activated charcoal can absorb and release fuel vapor forever, it doesn't wear out or get "full." However, there are filter elements within the canister (after all, it is an air intake) that may eventually get clogged, and the carbon itself may eventually get contaminated with fuel additives or other non-petroleum substances, so it is recommended the canister be replaced once in a great while.
If you're REALLY a skinflint, the carbon canister can be opened and the filters replaced. There are two, one at the top of the charcoal and one at the bottom -- you must dump all the charcoal on a newspaper or something. Both filters can be neatly replaced with coffee filters. The canister can be held shut with aluminum tape when reassembled.
Cannister Connections

The canister itself has an opening on the top to atmosphere, and three fittings on the bottom. The fitting labeled T is connected to the fuel tank, via the appropriate valve and the vapor separator. The fitting labeled P is the purge line to the engine. The fitting labeled C is capped off; it originally was the connection for venting the float bowls of the carburetors, but they are history. Note: if you fit carbs, do not simply open this fitting and try to use it; a screen has been omitted inside as well, and you will draw carbon granules into the floats.
Vapor Separator

In the XJ-S, there are several vent lines from the fuel tank. They all are routed to a small vapor separator high in the bodywork to the right and above the fuel tank. This small metal contraption is intended to allow most fuel vapor to condense and drain back into the fuel tank. The vent line to the canister is routed from a point high in this separator, so fuel vapors must be very determined indeed to make it past this point.
Note that the vapor separator has been blamed for many problems. Since it is steel, it is prone to rusting. If a hole rusts through it, fumes will be vented into the bodywork. Also, rust particles may fall inside it and plug the tiny vent passages and hoses.
Cannister Location

One of the possible causes of the common fuel odors is the location of the canister in the XJ-S. On most cars, it is located in the engine compartment where any escaping fumes will simply be blown away by the flow of air through the radiator. But in the location in the bodywork forward of the left front wheel, there is no such flow. The vapors may gather in the bodywork and eventually work their way to the passenger compartment. Of course, there aren't supposed to BE any fumes escaping, so this is a secondary problem. However, it might be a good idea to connect a length of hose to the atmospheric vent on the canister and route it out the bottom of the car.
Another possible failure mode is that the engine is not properly purging the canister. If the engine is not drawing air through the canister when running, the canister will quickly become saturated with fuel and will cease to absorb, and any further fumes coming down the vent line will escape to atmosphere.

 

SS - My understanding is that the only real fire risk exists from the rail hoses to injector perishing, M-ignition aside. My XJS has a fuel smell in the boot - I am resigned to it and it kind of mingles nicely with the Connolly leather - it is in fact its quite endearing to the character of the car.


Short of a fuel system rebuild as superbly detailed by Greg, let it go imo - the only thing I think he missed was disposing of the boot carpet once it stinks, it stinks.

 

That's the point, they aren't supposed to be "expanding" inside the tank, they are supposed to be venting to the canister, if air is rushing to get out it is tasking the walls,welds of the tank.

 

When the car is not run for extended periods of time, the amount of vapor generated in the tank could be considerable. Gradual changes in ambient temperature and barometric pressure would cause the vent system to "breathe", running a large amount of vapors through the canister. To absorb all this vapor, the canister would have to be prohibitively large.
To prevent this, there is a valve in the vent line between the fuel tank and the canister. This valve will allow air to flow in either direction, but only after a certain pressure or vacuum has been reached. If the contents of the tank expand and try to escape out the vent, it will prevent any flow until the pressure reaches a set value, and then it will allow it to pass to prevent damage to the tank or hoses. Similarly, if the contents of the tank contract and try to draw air in through the vent, the valve will prevent any flow until the vacuum reaches a set value, and then it will allow it to pass to prevent the tank from collapsing. As a result, the vast majority of the smaller expansions and contractions do not open the valve at all, and the amount of vapor the canister is expected to absorb is greatly reduced.
Of course, this means that at any given time the fuel tank and hoses may be slightly pressurized, even when the car is not running. Even the tiniest leak anywhere in the system may become quite significant.
Recall Modifications

The original XJ-S vent system pretty simply followed the description above. However, there were indications it did not work as well as intended (including numerous complaints about fuel odors), so there was a recall to address the system. As a result of the recall, there are components of the system that are positively operated by engine vacuum; in other words, valves that are opened when the engine is running.
Canister Replacement

You mention Recall Modification: do you have the official recall number?

 

Please do not toy with your fuel system, drilling the cap should never be done, those caps can be replace but never drill, better safe than sorry

If gas fume is being detected inside the cabin, the first thing you should check is the fuel sending unit located on the rear cover of your trunk between gas tank and carpet cover, take out that piece of carpet until you will see the fuel tank, and sending unit, sending unit is located almost at the bottom, usually that is the culprit, signs of gasoline leak can be visible out of the white round plastic where the wires are connected. Check this before proceeding to other component. update us.