My car is a 1992 XJS V12 roadster - What should I look for as the cause of excessive pressure in the fuel tank? The car has an after market external fuel pump as submersible stock pump was unavailable. Thank you.

 

Hello Morey

Saw no one replied to your previous post - so will advise what I would do to start things off

On the left hand side front guard - there is a charcoal canister that takes the vapour and equalizes the pressure as the tank expands and contracts during the day. If you disconnect this rubber hose (you should be able to see it in the wheel arch), this then should vent out any built up pressure in your tank.

Mine is a lot older than yours, but the principle should be the same - excessive pressure means the venting system is not working.
Should have nothing to with the external fuel pump, unless that original setup incorporated the venting system in the first place (something I do not know)

Cheers
Steve

 

Also, as a quick test, if Bez's plan does not crack it (probably will, but not if the tube to the canister is blocked), leave the cap loose on the tank filler and see if that cures it. If it does, you just have to make the tank vent work again.

 

Hi Morey

That setup sounds interesting!

Do you have any Photos of how it was done

 

Hello Steve, thank you for your quick response. We have checked this and the line is open to the canister. Three should be a valve in the canister that diverts the vapor back through the intake when the engine gets warmed up so one would think a slight vacuum would be created back to the fuel tank.

will let you know the results of our labor.

Thank you again,

Morey

 

Thanks, Greg, for your response also. You guys gotta be right I’m just frustrated because I haven’t what should be a simple problem.

Morey

 

Hello Orangeblossom, will try but don’t want to tear into areas not needed. Actual conversion was done five or six years ago.

Morey

 

The fuel tank air breathing line goes from the top RHS of the tank, on UK models via vapour cannister and a two way Rochester valve, through a very thin steel pipe along the back bottom of the tank and out in front of the LSH rear wheel where (on your model) it joins a pipe to the vapour charcoal thingy at the front.
The thin pipe along the back of the tank gets blocked, and if your model has a Rochester valve, that stops working too. If the front stuff is Ok, or at least the line from the tank is disconnected at the front, I would test the metal pipe by disconnecting the pipe where the join is in front of the rear wheel, and investigating what is there at the top RHS of the tank.
This is a pic of the pipe in question along the back bottom of the tank shelf:


You can see it rising up on the RHS to the flexible pipe from the tank and the Rochester valve.

 

Thank you, Greg, I let all know how we progress.

Morey

 

Thank you. Thought we had cleared that as a cause. Will revisit.

 

I failed to thank you as I did others. My apology. Thank you.