Do you know anything about these jeeps and fuel mileage? So I have almost replaced every sensor on this. Its a 96, 4.0, 4x4, lifted with 33's. It has a new t-stat, radiator and coolant. I have not changed out the gas tank (it has a dent from coming down off a rock) so I haven't changed anything fuel related and that includes injectors. I had to put in a new transmission (used) and new NSS. Recently the MAP, IAC, TB, exhaust o2 sensor before and after the cat, cannister purge valve and even checked for cracked elbows on vacuum lines. Before I installed the MAP and Purge valve two days ago, it was smelling really rich. I have not noticed the smell as of yesterday but my daughter drives it. Nothing has changed only getting about 10 mpg's. I used to get 16 to 18 even with 33's. I am not heavy footed and try to get the good mileage. I am in Phoenix, AZ and it's very flat here so there isn't a lot of uphill driving. I am at a loss literally. I don't know what else there is to replace.

AWG said to check for cracks in the fuel lines and put a scanner on it and see which codes come up.

 

let's be clear here because I think this I potentially key to the issue. Is the 10mpg what She is experiencing OR is that what the jeep is doing regardless of you driving it for a tank of fuel vs her?

With all the new sensors and such that sound like enough to have covered a running system issue. Perhaps this is her driving habbit alone that's causing the weaker fuel mileage? On the hand maybe it is in your fuel system - injectors or fuel filter?

 

I fill her tank up once a week and I do the math and it comes up as 10 mpg's.

 

So her driving style is a factor then

 

When you posted about this issue before it was appropriately suggested that you use your scan tool to look for codes and look at the fuel trims.
What did you see when you did that?

 

Replace spark plugs, differential fluids, air filter, then reset the ECM for a MPG boost.

Also OBDII to Bluetooth adapters are available. You'll be able to get accurate MPG.

 

Possibly low grade gas? I know silly, right? But have seen my fair share of videos and forum questions about gas mileage issues being resolved with top tear gas.
Back on earth though lol my xj gets 10 - 12mpg no matter what I do. And I drive it like a Lil old man ha!

 

You should drive it in similar use commuting as she does for a whole tank and see what the results are.

 

My XJs (on 30-1s with 3.54 autos) get 17mpg (Imperial Gallons which are different to US)

significantly better on the open road +20%, just short local trips, minus 10%

If your torque convertor lock up solenoid is not working, will cost 10-15% fuel economy

I believe a failing front O2 sensor will cause excessive fuel consumption

Do you have any heavy or windbreak stuff, such as winch, heavy bars, large roof racks?

 

That 17 mpg imperial is 14.2 US mpg. 10 is dismal. I'm getting 14-17 in my MJ, lifted 5.5" on 32s, AW4, 4.11 gearing and mostly rural highway.

X2 check that the torque converter is locking up. While cruising at highway speeds with steady throttle, lightly tap the brake with your left foot. You should see the rpm bump up as the torque converter unlocks.

 

Do you have a fuel system with the regulator up on top of fuel rail, or is it down in the pump. If on top...pull the small vacuum line off while running and see if fuel comes out of the regulator diaphragm.

 

That would take forever since she only drives to school and back and that is about 6 miles round trip. I drove it across town and back, about 60 miles and noticed the tank draining quickly.

 

How would you check RPM's if you don't have a tach? My cluster is all dummy.

 

I never got around to check for fuel trims. I just started replacing sensors, checking for vacuum leaks and so on. I figure I will replace everything on this XJ anyways as I don't have any plans on selling it. Project Dan on Youtube made an interesting comment that the fuel injectors can crack with excessive heat. Well since these 4.0's are notorious for that and I do live in Phoenix, AZ, maybe that is my problem. On Friday, I have to replace the power steering pressure hose and return hose as well as steering box that I ordered from Rock Auto. I know this has nothing to do with mpg's but there is a leak on one of the lines. I will get new injectors and hopefully put them in the weekend after. Does anyone have a recommendation for 4 hole injectors?

 

The only thing that makes that Jeep heavy is the lift, frame stiffeners, aftermarket bumper and oversized tires. Even the spare is oversized.

I am planning on installing gears to make up for the bigger tires. This may help a little or maybe A LOT?

I will check the spark plugs, but they were installed less than 20k miles ago. I will clean my air filter. The outside of the TB is dirty but I cleaned the inside last year.