Hi Guys
Just been reading through this thread and Id add my experiences too.
First of all, there seem to be numerous pictures of Barchettas in flames or burnt out on the web, it always seems to be most burnt around the o/s/f wing area. The fuel tank vapour purge canister as you probably know already, is in this area.
I too had the smell of fuel, present only with roof down or window open, no problem at all with roof up, window up. So started thinking that for the smell to reach the cabin it has to be coming from somewhere forward of that.
I disconnected the pipe under the rear floor, which carries the tank purge vapours to the canister and drove it about, no problems at all with fuel smell.
Now, on a VW, the purge valve/canister etc system operates as follows- you start the engine from cold, pressure gradually builds in the tank as the car warms up. This pressure used to be mainly caused by the dumping of warm fuel returned from the rail back to the tank. So legislation states that we can't just vent this vapour building in the tank to atmosphere, so its passed to the canister where it is "stored". Once the engine is warm and is operating in a certain drive cycle, the engine ecm opens the purge solenoid valve normally by duty cycle and the vapours are drawn from the canister into the intake and burnt in the engine. the canister has an opening to atmosphere so that air can be drawn in to flush the canister and also to prevent the engine collapsing the canister and even the fuel tank in some cases via suction. It also uses this to vent excess pressure of vapour to atmosphere in the case of a fault with the purge valve, pipework etc resulting in the system not working.
Like I said, I am/was a Seat tech so I can't say if Fiat is like this, but I bet its not too far off.
I tested the purge valve on my B and found it refused to open at all, no suck present at the pipe joint under the bonnet by the coolant tank. I tried this with it fully hot, at all engine speeds still didn't open.
I took the B for an mot a few days ago, it failed on Lambda too high. I eventually traced this to the Lambda sensor connector on the car harness side having its main signal wire broken at the connector, a small green wire.
I reconnected it temporarily and it passed the mot this morning.
The reason I mentioned this is because that wire has probably been broken/breaking for the best part of a year, you might remember I wrote a post on it when I first put the car on the road and had Lambda high at mot then.
My 2 points are 1, at no time over the last year have I seen any engine light come on and the car has been driving ok like it. I don't have a scanner to work on the B, so can't tell if any faults are set.And 2, a VW ecu would IIRC disable purge valve operation if faults are set. I wonder if the Fiat ones do this?
Oh, and I replaced the fuel pump assy and hose clips etc and still get a smell of fuel when filled to higher than about two thirds.
Regards
John