Unidentifiable Fuel Leak?

[dpbird90]

Think my Panda's leaking fuel but cannot for the life of me figure out where. MPG is reading much lower than normal (sub 30 where I'm usually getting 35-40) and according to the fuel gauge, I've used 1/4 of a tank within just 30 miles (although I know not to completely trust the fuel gauge, especially on a Fiat, after my old Seicento conked out while reading 1/4 of a tank left!).
I've had the car in the air, there's no visible leak on the tank itself, or on the fuel line. Looked in the engine bay, nowhere leaking that I could see (although with it pissing it down and being covered in oil, my judgement probably wasn't 100%). The last few weeks I've had a whiff of petrol whenever I started it up, but I put this down to the cold weather, thinking maybe this has something to do with it? Only other thing, I did have a loose HT lead which had caused the engine management light to come on, but this over was a week ago.

Any ideas?

[E30M3SE]

Faulty cold start sensor.

[dpbird90]

thanks, virtual pint to you! How easy are they to replace i.e. is it something I could do myself or will it be a garage job?

[8balls]

First, check spark plugs - if one of them is black you know that cylinder is running rich and you might have leaky injector.

If all are of same colour (and you are not leaking fuel outside the car and you cant smell gas) then it is most likely either leaky cold start injector (injecting fuel to intake manifold so all cylinders are running rich) or even more likely faulty cold start injector switch. If this temp sensor controlling cold start injector is broken it is easy to replace.

However, first the obvious things - how about the temp gauge? Does raise to normal level? If not, then cold start system works normally, but engine never heats up because (most likely) faulty thermostat...