Basically the title. I know its a thing thats been discussed many times, but I cant come up with any solution with the typical checklist. MPG is horrible, around 8-10 (or 25-30 L/100km) in the city. 1992 XJ Limited. 140k miles / 230k km.

List of things changed/replaced over couple years:

- Whole exhaust system (new header, cat, muffler, pipes, 02 sensor)
- Sensors (TPS, IAC, coolant temp, map, IAT etc.)
- several thermostat 190-200
- fuel filter, injectors, fuel pressure regulator
- Checked for vacuum leaks (replaced all lines), cleaned throttle body, air filter, cleaned intake manifold
- spark plugs, distributor cap, rotor, wires
- no dragging, rolls easily on neutral, brakes replaced, stock size tires

Let me know if you can come up with any ideas. I'm all out.

The jeep runs great. It has power, it doesnt stall, starts up well, idle is great. Everything is fine, except for the fact that I get 200-250km (130 - 150 miles) with full tank of 65 liters /17 gallons.

 

1) check the compression

2)) which transmission do you have??

 

PCV valve, check compression. Mine's a lifted 96 with 33's and 4.56 gears and I am getting 14 mpg. I did replace everything you have except exhaust pipes, fuel injectors and regulator.

 

Assure your oxygen sensor is new, this is a consumable item and needs periodic replacement. Assure you dont have dragging brake(s)!!!! assure your torque converter is not slipping if automatic tranny, you can tell this by the rpms if it is slipping the rpms will peak.
With your high fuel use, Id be concerned you may have a very rich mixture, this will rapidly destroy your catalytic converter, so get it fixed, rich running will also wash down the oil from the rings resulting in excess piston cylinder wear, and can dilute the motor oil with gasoline, which aint good for bearings!
You may have a leaky fuel injector. You can check the injectors for flow rate.
by checking the spark plugs you might see one or more showing signs of running very rich, which may point to a leaky injector.

You mileage may vary, but your is much too bad, so you got a problem.

That is a very nice looking XJ you have, thanks for the photo!

Where you live at?

 

I hate to be the jerk to say this, but are you sure your measuring correctly. My stroker with 20% more displacement, 20% larger injectors / 31's on stock gearing 3 inch+ lift and a giant roof box gets about 15-17 on total highway...13-15 mixed and 12 ish on total local driving. You have changed all the suspect parts. If you only got 8 mpg your jeep would reek of fuel. With apologies...fill to pump cutoff...record mileage.....drive until you refill, im sure you don't refill at total empty -17 gallons. Record mileage and gallons to pump cutoff...do the math... miles divided by gallons. If your really getting 8-10 mpg your plugs would be black with soot...pull one and see

 

Charley3 almost cracked 25mpg with his XJ without doing anything stupid crazy or weird.

https://www.jeepforum.com/threads/my...5-ats.1551782/

As part of routine scheduled maintenance on my 95 DD my milage went up as I did the tune up, the cables, the grounds, the sensors and exhaust.
One thing I did that Charley3 didn't before he quit driving was the Dodge dynasty fuel pressure regulator required on pre 97 to run 12 hole injectors in pre 97 Jeeps.

Another thing you can do is keep the speed down to 60mph whenever practical.
Our Jeeps are essentially brick shaped. Push a brick through the atmosphere bove 62 mph/110kph and the aerodynamic drag goes way up and sharply.

Getting 90% of the interior space of the full size SJ Cherokee better suspension articulation more power and like 50% better fuel economy in exchange for "boxy but good" was a damn good trade off back when the National speed limit was 55mph.

 

Type of driving makes a huge difference in MPG.
Slow short distance (especially in cold environment) trips, engine wont get warm enough. (+190-200F)
resulted in 8-9 mpg.

Suffered poor mpg with a dirty IAT (use proper spray).

I do many slow short trips. Took extreme move and went with 2 stock XJ electric fans trigger by relays.
Warms up much faster and free up some engine drag (+1 hp). But mileage went up a lot.
No issue with overheating. But havent done high load in high heat and at super slow pace.

Also consider vacuum leaks, definitely affects MPG. Usually starts on first crank.. With a leak took 2-3 cranks, mileage went from 16 to 14.
1996 4.0 5 speed

good luck