Well, the unofficial results are in. I did over 100k's of mixed driving today and the Jeep is running so smooth and the economy has definitely improved.
Just to recap, i fitted a touch screen MPG gauge to my OBD1 XJ 4.0. Wired through the injectors and speedo. After calibration it is very accurate and can give me instant and avg lt/100, distance to empty etc..
After getting base readings of avg combined 18.2 lt/100 and an 80kph (50mph) reading of 14.5lt/100 a few weeks ago, it was time to do some work on the Jeep to improve things.
This included swapping out the ZJ clutch fan to a Hayden XJ clutch fan. New O2 and MAP sensors. Pump tyres up to 40 PSI. New fuel filter. G70 friction modifier in diffs and Nulon E10 in engine. Reset computer.
After driving today, the computer is adapting well and bringing the economy back into check. At 80kph i now average around 12.5lt/100. This is a US 18.82MPG. Combined at the moment is averaging around 15.9lt/100 which is a US 14.79MPG.
Considering my XJ has a lot of mods and weighs a lot more, i think the figures are starting to become reasonable. A brand new unmodified 1998 XJ 4.0 Auto had an official government EPA rating of a combined 16MPG and 19MPG highway rating.
https://www.fueleconomy.gov/feg/noframes/14742.shtml
I'm not far off those figures now. A steady foot helps alot. Also, my transmission has the power/economy button. Economy locks the torque converter up at 45/50 kph (power setting is about 70kph), so that driving around town, i notice it uses a lot less fuel.
Cheers,