Loosing MPG's fast!

[Mayooo]

To start, this is all based on my everyday driving. Wheeling was not involved in these calculations.

I'm a light foot driver. Mostly because I need to stretch every penny of fuel in my semi-truck and it just carries over to my xj. BUT I'll drop the hammer if I need to. HA!....

Anyway, I've been getting terrible fuel mileage and it's just keeps getting worse.
When I first got the xj I was getting about 260 miles per tank, about 16mpg. The only mods done at that time was a 2" block lift and 31's.. All been done by previous owner. I did do a full tuneup when I purchased the jeep.

As the building started with the roof rack, winch bumper, 33's A/T and various recovery/tools placed in the back. The milage dropped to about 200 miles. About 12MPG which I expected.

Now with the current phase of the build, 4.5" lift, 33's M/T, spare tire mount, more recovery gear/tools, rack mount hightlift, cowl snorkel, more LED lightbars and DIY fender flares to accommodate the cut fenders front and back. I'm getting about 180 miles. About 11MPG.

Now this is where it takes a turn. I've been getting 11mpg for a good 1/2 year now. But recently it's been dropping like a rock. 10mpg, 8mpg now at 7mpg.
The motor idles and runs smoothly. One of the things I'm thinking but haven't checked yet is a cracked manifold. I can hear tapping and exhaust leak but don't see anything wrong from the cat back that I recently replaced. Throttle body is clean and from the coil to the plugs all have been replaced before winter. I've gone over the typical checking of the air cleaner and even put in a new fuel filter. Motor was de-sludged back in August and everything was flushed. I'm also wondering about my vacuum lines and plan on replacing all of them here in about a week or so because they are getting pretty old and brittle.

The next move for the xj build is to work on the performance and try to reclaim MPG's I ordered today a new exhaust ceramic coated long pipe header and a high-flow cat with new piping and a 24" glass pack(cherry bomb).. My ignition will also be replaced with a coil block. I'm hoping this will get some MPG's back.

So basically that's my plan this month. Is there anything I'm overlooking or missing? Will work or not? Any ideas on why my MPG's are dropping rapidly?

Thanks

[Mudderoy]

To start, this is all based on my everyday driving. Wheeling was not involved in these calculations.

I'm a light foot driver. Mostly because I need to stretch every penny of fuel in my semi-truck and it just carries over to my xj. BUT I'll drop the hammer if I need to. HA!....

Anyway, I've been getting terrible fuel mileage and it's just keeps getting worse.
When I first got the xj I was getting about 260 miles per tank, about 16mpg. The only mods done at that time was a 2" block lift and 31's.. All been done by previous owner. I did do a full tuneup when I purchased the jeep.

As the building started with the roof rack, winch bumper, 33's A/T and various recovery/tools placed in the back. The milage dropped to about 200 miles. About 12MPG which I expected.

Now with the current phase of the build, 4.5" lift, 33's M/T, spare tire mount, more recovery gear/tools, rack mount hightlift, cowl snorkel, more LED lightbars and DIY fender flares to accommodate the cut fenders front and back. I'm getting about 180 miles. About 11MPG.

Now this is where it takes a turn. I've been getting 11mpg for a good 1/2 year now. But recently it's been dropping like a rock. 10mpg, 8mpg now at 7mpg.
The motor idles and runs smoothly. One of the things I'm thinking but haven't checked yet is a cracked manifold. I can hear tapping and exhaust leak but don't see anything wrong from the cat back that I recently replaced. Throttle body is clean and from the coil to the plugs all have been replaced before winter. I've gone over the typical checking of the air cleaner and even put in a new fuel filter. Motor was de-sludged back in August and everything was flushed. I'm also wondering about my vacuum lines and plan on replacing all of them here in about a week or so because they are getting pretty old and brittle.

The next move for the xj build is to work on the performance and try to reclaim MPG's I ordered today a new exhaust ceramic coated long pipe header and a high-flow cat with new piping and a 24" glass pack(cherry bomb).. My ignition will also be replaced with a coil block. I'm hoping this will get some MPG's back.

So basically that's my plan this month. Is there anything I'm overlooking or missing? Will work or not? Any ideas on why my MPG's are dropping rapidly?

Thanks

You didn't mention when you last changed the O2 sensors.

[Mayooo]

Still the same O2 sensor since I got the xj. Was thinking about changing it and that it might be part of the problem.

[Mudderoy]

Still the same O2 sensor since I got the xj. Was thinking about changing it and that it might be part of the problem.

I think that is usually the problem at least on the 97+ XJ's

I would try the O2 closest to the engine first.

[prerunner1982]

Did you regear? Not the issue of the dropping mpg, but would help get some of the mpg you lost by going to 33"s.

New plugs,wires,rotor wouldn't hurt...

[4.3LXJ]

If that header has a leak, that generally will make them run rich, as well as worn out O2 sensors. I think it is time to address both.

[Mayooo]

Just ordered new o2 sensors And give that a try. This continues rapid drop in MPG's just developed over the last 3 fills.

[Mudderoy]

Just ordered new o2 sensors And give that a try. This continues rapid drop in MPG's just developed over the last 3 fills.

Next step, make a sail and learn how to tack!