Chasing fuel economy? Lose some lift

I'be been chasing down my 2001 XJ's abysmal fuel economy (~11.5 mpg) for months at this point... Completely new exhaust (thinking a major manifold leak was making it run rich), new NTK O2 sensors, new spark plugs, new 4-hole injectors (both 784s and 007s, both of which throw off the OHC fuel economy calculations), and through all that, I only managed to obtain a mild improvement, ending up at around 12.3 mpg.

Having abandoned all hope, I turned my attention to the ride quality of my old RE 3.5" Sh*ttyRide springs. I ended up installing OME 2930 coils (adding an inch to them via ACOS) and removing the second smallest leaf from the RE1463 leaf packs (which never settled any, even after 7 years of abuse). I also ditched my drop pitman arm due to obnoxious bump steer issues. Bilstein 5100s were retained through all of this (6" lift models up front, 4" lift models in the rear). All in all, I lost about 1.5" up front, and 3/4" in the rear (I wanted a bit of rake for loads anyway).

After that, something magical happened. I'm now averaging over 15.7 mpg (!) over two tanks of gas thus far.

My best guess as to why the impact was so substantial is that previously, the entire front profile of my tire (265/75R16) was exposed. I'd always read that turbulence of air flowing across the top of a rolling tire creates a huge amount of drag, but this definitely confirms it. Now, the top inch or so is hidden behind the bumper.

In any case, the ride is VASTLY improved, as is fuel economy. Figured I'd share.

How does the injector size or hole count change the ohc readings? The computer measures the air/fuel and combined with O2 readings, it calculates fuel consumption. So unless O2 is wrong, how could it not notice?

Am I missing something?

The overhead trip computer calculates fuel economy based on the injector pulse width, which the ECU adjusts based on O2 sensor output (in 2000 and 2001 models, it turns out both upstream and downstream sensor inputs are used for fuel trim adjustments). The 784 and 007 injectors have a higher flow rate than the stock injectors, meaning shorter pulse widths to deliver the needed fuel than would be needed when using the stock injectors. Shorter pulse widths trick the computer into thinking less fuel is being used, leading to inflated and inaccurate fuel economy numbers. Talyn (I think?) has broken it down really well in past threads about these injector "upgrades", but it has absolutely been confirmed in my experiences. The 007's throw the trip computer off by about 5-7%, whereas the 784's throw it off upwards of 15% (can't remember the exact number, but it was asinine when compared to manual mileage-based calculations).

Awesome explanation, my brain wasn't quite ready to think that deep this morning.