I get really shtty gas mileage. 10 mpg mostly, roughly 180 gallons per tank. Very small lift and 31inch KO2s and brand new 4 hole injectors and smooth driving seems like I should get a little more. I’ve got a friend with stock injectors, 35s and 5 inch short arm lift, he still gets 15-17 mpg. Is there other things that equate to bad mpg on these cars, like failures to look for.

How long since your O2 sensors have been replaced?

What axle gear ratios are you guys running?
any check engine lights?
Did you reset the ECU when you installed the new injectors?

Reset ECU I think (touched terminals together for a while and turned on headlights), 3.55 gears on mine, downstream sensor replaced at 158xxx miles, I’m at 161xxx now, no CEL.

make sure your brakes aint dragging. do a general engine test. compression, manifold vacuum, inspect spark plugs, ignition wires, check fuel pressure. run a diagnostics on the sensors. check that torque converter is locking as it should.

I get 15 to 16 mpg* on level highway at 65 to 70 mph. 33 x 12.5 tires, 4.11 gear, 1990 4.0 liter automatic. loaded with lots of gear, rocks rails, roof rack, winch jerry cans, camp gear, etc...

* crummy california enviromental gasoline, loaded with oxygenates, which gives near 10 % less energy per gallon, costs more, and actually has a larger carbon footprint that normal gasoline when its production is taken into account. (not that I believe in that "earth has a fever cause of CO2" stuff anyway)

Drill baby drill!
$6/ gallon is what it is near me. ugh!

New Spark plugs and wires gave me +3MPG

How are you calculating the MPG?

My xj has a 18 gallon tank correct? Roughly 180 miles per tank would be 10 miles every gallon

The only time my 1996 XJ sees more that 16 MPG is when the crank sensor is going out. Usually I get 14/15 MPG.

How is your coolant temperature? Mine runs lower MPG when the thermostat opens too cold (fixed by putting the original factory thermostat back in and tossing out the new junk). Should be a straight up needle around 210/215 F.

That's not how mileage is calculated.
Fill the tank and record the odometer reading.
When you fill next, calculate how many miles were driven.
Take the number of miles driven and divide that by how many gallons you put in. That's how you do it.

Thats what I did

Not according to Post 8.

I must have not written post 8 correctly. I fill the tank up with 18 gallons are less to fill it. My odo reads 180ish miles more than when I was at the gas station

Doesn't work that way.

Can you explain more, I’m confused