Did you miss the part about varying the speed? I tried 60, 65, 70, and 75. No change.
I have noticed that past 55mph, fuel consumption is roughly the same between 65 , 75 or 85.
I don't drive Jeep faster than 65 mph, so i had very little interest in establishing exact miles per gallon difference between speeds. What i would do during long road trips, is drive 120 miles at 65mph and other 120 at 75 or 85, and in the end i would still end up at my rough 240 range on 17 gallons.
I don't know what physical forces go on in front of a Jeep at highway speeds to explain this phenomena, but that is my observation.
For the sake of your own sanity, come to understanding that half of this 19mpg clowns are either full of shit or have their facts backwards. Other half have their Jeeps running on unicorn farts.
I understand the desire to go into "WTF?!" mode when someone claims 19mpg while your barely scraping the surface of 14.5mpg, but those miserable 14.5mpg is the norm... Matter of fact it is ignorant to claim 14.5mpg as average, since the actual fluctuation is 11 to 14 mpg. That is the reason why i despise retarded american system of mpg, while rest of the world uses liters per 100 km. It is simply dumb to keep track of every mpg instead of looking at your overall range or the average per so many miles.
In the end i will say this:
Two other cars that i drive is Toyota Tacoma (19 mpg) and Acura MDX (22.5 mpg). They consistently produce repeatable fuel consumption figures. In those cars i can lean back and drive them with a pinkie finger.
So when someone, who drives 18 year old square box, that gets blown off the road with every wind gust, comes around and claims as much of fuel efficiency as my two other cars, i simply turn off the computer and go do something else... cause the desire to "reality check" some people is sometimes hard to resist.
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As far as improvements:
1. Get a computer that hooks up to OBD port and observe your throttle position. Over the years of being as passenger, i have came to a conclusion that some people have no feel for things. They do too much of gas- no gas- gas- no gas- gas thing with pedal, and there is not a damn thing you can say for them to understand that it is a retarded way to drive a car. This may or may not be the way for you.
2. One time i had to replace O2 sensors 3 times in the row. Reason is one of them was defective, just as bad as the old one. Other two were kept going out due to a valve cover leaking oil, and that oil would make its way down the exhaust manifold and drip on the sensor.
3. Exhaust leak at the manifold. That leak confuses a computer, which will produce wide fluctuation between good fuel efficiency and very bad fuel consumption.
4. One person had issues with a bad cloackspring. For him, it was doing something that was messing with injectors. Something something, in other words if you have signs of misfire/ rough idle, that may be the case for you....
Holly efing shite, that was a lot... sowwi