Blocked fuel pressure regulator can also cause high fuel consumption.
These are located on the back end of the fuel rail (inlet manifold), at the firewall.
Pull the vacuum line, remove the large "C" clip, remove the guts & check the gauze filter.
I hate mechanics that "guess'.
If your vehicle is not running normally, then there's a reason for this. Taking the "logical deduction" approach should quickly lead you to a problem part.
Ie: if a tyre is flat, it's a waste of time changing wiper blades!!!
I will add though that it's not unreasonable for an XR6 to use upto 20L/100km doing short drives.
Falcons are renowned for being fuel guzzlers. Try using the economy setting (auto trans) or just go easy on the go pedal for a week.i
My stock AU2 sits on about 16L/100 around town & around 9 - 11 on the highway. It is high but the point has been proven.
its good to hear all this information.this is a short drive xr6 but has the get up and GO behind it.maybe a good highway drive wouldnt go astray