I have a Jaguar XJ6 4.0 straight six X300 on a 1997 plate. It was recently doing really bad on fuel. So I ordered a new MAF sensor and fitted it. It seems a lot better it seems to be giving nearly 20 mpg round town and more on a run. Before it was doing really bad on fuel and you could smell a petrol smell strongly. Now the petrol smell is a lot less and only just noticeable. Any Ideas on what to change would be greatly appreciated ?. I was thinking spark plugs, lamba sensors, Faulty coil pack maybe but not 100% sure. I also got told maybe temperature sensor but the temperature gauge sits at half when in traffic. When your driving it goes down to about quarter I thought that was maybe because its cold outside.

 

Thermostats are prone to stick open. I'd get a cheap OBDII adapter and watch the temp. The gauge is highly "approximate"
That would account for sub-standard fuel mileage but don't think you should be smelling it.

 

Is the engine still running rough in any way or do you now only smell fuel? Any signs of leaks ? The fuelfilter is located above the rear left wheel. Maybe see if there are signs of leaking or just change the fuelfilter. Around 20mpg around town is about what you could expect from these cars I guess. The famous bracket from Andy is said to both improve performance and mpg. I installed it and it was a big difference in performance but I have not measured any fuel usage yet.

 

Not sure, but I assumed OP is getting 20 mi per Imperial Gal, which is a bit shy of what the UK lads have been reporting. I have always achieved 20 +/- .5 per US gal with a mix of about 50/50 city-hwy.