[cheapfix]

After getting my XJ road-ready, I was horrified to find that my first full tank of fuel resulted in 11mpg, even after new plugs, wires, cap, rotor, and air filter. This was mostly rural commuting with few stops and low speeds, with a bit of light, in-town, grocery-getter use as well.

No codes stored, and I checked the CTS, MAT, and MAP sensors with a multimeter, which were all within range according to Haynes.

Here are the changes I made, which combined to improve the mileage to 18 in the same mixed commuting/town conditions:

1. Removed existing exhaust/cat and replaced with 2.5" muffler/pipe (used, but in good shape, from my parts waggy)
2. Removed existing downpipe and hammered almost all of the "dent" out at the top of the pipe (couldn't use waggy's nice, newish, 2.5", undented downpipe, as it is a renix and is a different shape)
3. Seafoam through the tank, highly concentrated (1 can with 25 litres of fuel) and drove it hard until that was burned)
4. New O2 sensor
5. Left trans in "comfort" mode instead of "power" mode.

Draw your own conclusions as to which is most responsible for the increase. I think it is primarily the 02 sensor.

"Comfort" mode seems to not only shift at slightly different points, but seems to lock up the torque converter earlier, which helps.

Without the cat (I know, I know, I am going straight to hell for this) and with the exhaust moving more freely, there is a definate "seat of pants" improvement in power.

As always, YMMV.

[nrpalmer32]

So does the seafoam smoke at all once you pour it in ur gas tank? And about the cat, I would LOVE to do that too but I have to go through DEQ pretty soon. And from my experience with the "Power" and "Comfort" settings, I know the comfort shifts at lower rpms which I would think give better gas mileage but I think I get a little better in Power mode? maybe I'm just crazy but it seems like it. Thats a HUGE increase in MPG tho, good job!

[cheapfix]

No smoke from seafoam when run diluted through the tank - I think it mostly cleans the injectors used this way, but might remove some of the carbon and deposits as well (?).

[photonut13]

Thats an amazing mpg increase i have to say, I would also like to remove the cat and put in a strait pipe but I have to wait till 2011 when my Jeep becomes exempt from the drive clean program up here in Ontario Canada.

[SoloCamo]

Spare your transmission's life and keep it in power mode. I also got better MPG in power mode as well.

[steveinwv]

Originally Posted by cheapfix

Without the cat (I know, I know, I am going straight to hell for this) and with the exhaust moving more freely, there is a definate "seat of pants" improvement in power.

As always, YMMV.

The holy grail of Jeeps, the CJ, when equipped with a V8, never, ever has a catalytic converter within 20 feet of it. We are talking about an inefficient, carbureted, point fired (usually), gas using machine that everyone loves. No converters anywhere! Soooooooooooo...................I'm thinking that removing the converter from a 4.0L, fuel injected, computer controlled engine isn't such a big deal, except from a legality standpoint. And if you don't get caught, it ain't illegal, is a good rule of thumb at that point.

I'd rather have an 18 mpg Jeep with no converter, than a 11 mpg Jeep that was politically correct.

You've done well, grasshopper.

[cheapfix]

Originally Posted by SoloCamo

Spare your transmission's life and keep it in power mode. I also got better MPG in power mode as well.

I will run a couple of tanks on each mode and see if there is any difference. I like pwr mode as well for the crisper shifts, but unless you are under heavy load, or have a total lead foot, I don't think that comfort mode will do the trans any harm, and it does lockup the TC earlier.

There are probably half a million Supras and Cressidas and 4runners out there still running around with AW4s whose grey-haired owners never switched to power mode!

[BrunoS]

replace fuel filter as well.

put 35 psi air in tires.

remove roof rack.

18 mpg is pretty good.

20-24 mpg for me right now.

keep the cat.

[ninobrn99]

id say most of it is from the o2s being changed out. they make a dramatic change!

[Toms_MustangGT]

Originally Posted by cheapfix

No smoke from seafoam when run diluted through the tank - I think it mostly cleans the injectors used this way, but might remove some of the carbon and deposits as well (?).

It smokes if you undo the PCV line and pour it in while the motor is running, but somebody has to be on the gas to keep the car from stalling out......and it will give a nice smoke show for your neighbors.

[geewally9]

Geez I guess I need to update my stuff. 13mpg is killin me.

[TehHelmet]

Originally Posted by Toms_MustangGT

It smokes if you undo the PCV line and pour it in while the motor is running, but somebody has to be on the gas to keep the car from stalling out......and it will give a nice smoke show for your neighbors.

Thats not true from anything I've read. It's my understanding (someone correct me if I'm wrong), that you are supposed to pour it in slow enough that the engine doesn't stall.... I've read a lot about it but I've never done it myself. From what I've read, when you pour it in (at idle speed), you do it so that the engine almost stalls but not completely. Obviously there's more to it than that but I don't believe that it is a two person job by any means.

And geewally I agree, me too. However, If I'm on flat ground though at 70-75mph, I can watch my ECO meter on the trip comp vary between 20-26mph consistently. Now, around town, going up and down this hilly state, yep.... 10-13mpg buddy. Of course, it doesn't help that I still haven't done my gears and I'm running 33's on 3.55's.

Edit: now that I've been commuting about 35-40 miles a day for work, I've been seeing an average of about 17-17.4mpg. Not tooooo bad but more is always better.

[Jamesss]

Man I have to breathe the air the same air that you are dumping all that **** in without your cat. Put it back on!

[geewally9]

Originally Posted by Jamesss

Man I have to breathe the air the same air that you are dumping all that **** in without your cat. Put it back on!

lol here we go agian. No worries though, with how the air flows around the world, by that time his air reaches you, his little cat will be the least of your breathing problems.

[steveinwv]

Originally Posted by Jamesss

Man I have to breathe the air the same air that you are dumping all that **** in without your cat. Put it back on!

I'd be more worried about the thousands of planes in the sky that burn fuel at an unbelievable rate. A 767 that burns one complete 'tank' of fuel probably puts out more **** than a Jeep without a cat will in its lifetime.