I'm just coming back to this tread as I had a gauge issue that I think is cured now but when I was at it I found out some info that may be of use.
I noticed a while ago when I filled up the gauge was very slow to rise and I thought there may be a problem in the tank, it took about an hour to get to a true reading of what fuel was in the tank, the next time I filled up it was fine. It wasn't until I had a run over to Whitby that my fuel light came on with 30 miles range and and I filled up with fuel that the gauge didn't move upwards at all and just kept going down to zero, I knew I had around £60 worth of fuel in so I just drove home knowing I had enough.
I stripped the battery and battery tray off to get to the top of the tank and sender unit, I had thoughts of the tank being collapsed again but when I pulled everything out the tank was fine and I started to swap parts over from my other fuel senders, I used a cleaner actuator arm and refitted everything. Nothing was binding so I think it was just a bad reading. I refitted and have filled up twice since, both times getting a true reading.
Now this is the reason I am updating, I found the 3.6 cars do actually have a fuel filter and I also know the reason when the tank collapses the sender fails at the same time other than just the stand bending.
This is the fuel sender scale and after switching an old one over, as I thought this may be my gauge problem and after installing I found out it didn't work and then realised why, there was a hairline crack in the board and any time the tank collapses it'll damage this as its very brittle a little like ceramic.
When I removed another one it fell to pieces, it was already broken in it mounting. I refit the one that was already fitted.
I also decided to change the fuel pressure regulator as I suspected it may be this causing some running issues, this didn't make any difference to the running but this does show you how to replace it if you ever need to.
And I also found whilst stripping the sender unit down a fuel filter, I'm not sure if it available separately but this is good news if you are chasing a fuelling problem. This one looked fine and with the screen filter at the base of the pump I suspect they don't get dirty very often.
I can easily be got to in less than an hour.
I did eventually changed the whole float assembly as the one fitted that connects the sender scale was a little dirty and I think this did cure the dodgy gauge, or at least I hope it has?