I have a 98 XJ that is bone stock if my calculations are correct I am getting 16 mpg (mainly highway) and I'd like to improve it as much as possible, what can I do to the Jeep to improve fuel mileage? Any advice and suggestions are greatly appreciated. Thank you.

 

Drive the speed limit, make sure your tires are inflated properly or even a tad higher, remove excess weight, keep it tuned.

 

Do a tune up!

Add BG 44K to a full tank of gas then replace plugs, wires, cap & rotor and air filter. Ensure tires are properly air up and balanced and it wouldnt hurt to check your alignment.

 

Perfectly said. Those are the only things that will increase mileage, and they're all free, or almost free to do.

 

Keep up with regular maintenance. And when your exhaust starts to fall off replace it with a 2.5" system with a high flow cat and muffler.

But for now a tune up should do it. Make sure your brakes aren't dragging, one did on my 89, it was not fun lol.

 

A block of wood tied to the bottom of your gas pedal usually works.

 

you could do the injector swap. i did it on my 95 and saw noticeable fuel milage improvement, however, my stock injectors were pretty junked up so that could definitely be part of it.

here's some more info on it from another forum member: https://www.cherokeeforum.com/f2/did...wap-wow-44404/

just to give you an idea of how my fuel economy improved, I was getting about 180 miles to a tank prior to doing the swap. now I get about 210. i fill up right around a 1/4 of a tank.

 

First and foremost, learn to accept that you are not going to get much better mileage with an XJ. I did the full tune up, new plugs/wires/cap/rotor/air filter, cleaned my intake manifold and throttle body, and I still check in at 15.5 mpg. I also have a heavy winch bumper on the front but even before that I wasn't getting much better.

One popular thing to do is to swap your injectors with 703 injectors from Neons and other cars. (search) I have yet to see any significant mileage gains from this mod reported around the forum (haven't done it myself yet), but you may have better idling and faster startup.

 

Why is it that fuel mileage claims seem to be all over the place? Even talking factors like tire size being equal, some claim around 20 and even better, while others in the 15 range?

 

A big portion of it is varying definitions of "tuned". Lets say a typical XJ is 18 years old with 200k mi. That's far from new. At that point a "tune up" means pretty much EVERYTHING. You can bet all the sensors are lazy, the grounds are crappy, the wires are corroded, the passages dirty, the cams worn, the valve springs lazy, the rings loose, the exhaust plugs and leaky, etc. never mind the spark plugs and distributor cap. Much depends on how the vehicle was and is driven and maintained. That's the short answer lol.

 

There's just too many factors at play to really determine a solid answer to this question. Regional gasoline mixture differences, driving habits, the condition of the engine and all the systems that make it work, hilly areas vs. flat, manual vs. automatic, how the person is measuring their mileage, lifted and big tires and whether they changed out the speedometer gear to get the proper numbers, gearing ratios, the list goes on.

For what it's worth for my mileage, I live in hilly south-central Pennsylvania. I calculated by filling the tank as far as it would go, reset the trip meter, and drove about 100 miles. Refilled again till it wouldn't go anymore, and divided the 100 miles by amount of gallons it took to refill.