I read the posts regularly and I find fuel consumption on jtd to be very interesting subject. Most of the time it is too high specially for 2.4 jtd/jtdm drivers.
Here is my experience and numbers Alfa 147 jtd 16v remapped to around 170 hp, oil total quartz 9000 5w-40, tires good year eagle f1 asymmetric 2 225/45/17 :
Best MPG: Around 65+ UK imperial mpg extra urban driving , all driving is done at 1500-1600 rpm. Mostly 5th and 6th gear , no overtaking, no quick accelerating. Shifting to neutral on downhills when possible. Trip lengths about 200 miles. Board computer shows around 10 % less fuel consumption.
Worst MPG: 37 UK imperial mpg combined flat and mountain roads. Maintaining around 80-90 mph on flat highways overtaking with full throttle 50-100 mph, to the red line most of the overtakes. Full throttle on strait incline roads up to the red line in each gear, fast in the corners up until tires start to make noise . Trip length 100 miles. Board computer shows 22% less fuel consumption.
Everyone with high fuel consumption try to remap first, then try my tips for best mpg and post the result