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Hi guys, it’s my first post. (Mark needs some company here!)
I’d grown accustomed to the whiff of fuel every time I opened the boot/trunk of my 1987 XJS 3.6 Coupe. There had always been a trace of it from new! Last week, I noticed things had got a lot worse. The inside of the car filled with a fuel smell and when I checked the boot-well, there was a small pool of fuel just under the fuel sump tank. OK, tools at the ready, I’m on the trail of the leak. I’ve drained the tank – not that I could get the drain plug to shift! All hoses seem OK. I’ve got the pump out – seems OK. I’m now looking at the sump tank. I’m going to try pressure testing it this week. There’s some pitting in the base but I can’t see that a pinhole here could be the whole story. The main tank looks perfect and I’ve never ever seen any water in the boot-well or suspected that the rear screen leaks. I also can’t see how any fuel would have run from it to the well without leaving a trail. I’d really like some pointers for next weekend: Do I need to get the main tank out to get to the bottom of this? So to speak!

If you can't find a problem with your secondary tank, then I'm afraid its time to take the tank out. They tend to corrode at the bottom (although one would think they are in the driest part of the car).
Pratical tip - go the long way around the job and remove the fuel filler assembly including the inner metal tube that feeds inside the main spout of the tank before trying to wiggle the tank out; then be patient, it will come, just not all at once!
If you go down the secondhand root for a replacement tank, make sure there pipes attached, as yours may not be compatible, and I would also investigate the fuel tank lining system sold by Frost before installing.
Having just watched the news, get it sorted quick!

Robin Gripp

Dear mark

first thing look at is the black padding uder tank and if that has got petrol on it you need to remove tank because of either rust or split because of high presure does it have the presure mod on vent in boot should be wired into the fuel pump

best regards paul.

Sorry about the delay in adding comments on a fix here but the XJS is in my (cold) annex garage and I'm waiting for a warm day to get stuck into this problem again. I've been saving for a new main tank - this looks increasingly like the solution.