My Best MPG!!! Trust me it's not what you Think...

Believe it or not, 400km's to a Tank, thats 250 MILES. Thats 12.5MPG
I openly admit that I drive like a little bitch, revs do not exceed 2000rpm, I hardly speed

I have a 96' 4.0L with the 20 gallon tank

city driving for the most part I eliminate as much stop and go as possible traveling at 70km/h (40ish mph) on the highway I usually putt along at 100-110 (70ish mph) I can't afford a speeding ticket

Revs on the highway at 2000rpm going 110km/h
235/75/15
Running Amsoil in the engine, just running plain jane dexron in the Tranny because I have read on here not to switch to a multi purpose synthetic.
I should change my tcase and diff fluid, checked them out on Saturday and they looked and smelled "ok"

My exhaust was replaced in 2002, what could the chances of the cat being the culprit? Bad 02 sensor? Mine is a 96'

My air filter is dirty as sin, I just called and ordered up an Amsoil EA229 air filter for the stock box.

Not sure the last time the ignition components were replaced, I bought it back in October 2006, I am planning to redo the ignition system in the spring. Anything else to look out for? Tires are properly inflated, will be rotated on my next oil change.

Edit: To rule out the cat, then I did my etest it passed with flying colours! If my cat was plugged would I fail an etest?

Since you passed emissions, your cat and O2 sensor must be working fine.
I don't know how you can get only 400km per tankful from a 4.0 driving like a granny. I get more than that from my 4.6 stroker (6.8-7.4km/liter) and I drive my Jeep a lot faster.
Do you have a roof rack, suspension lift, or any added weight that could be hurting gas mileage?

I have a stock roof rack but other then that, no added weight. The only mod I have done is a CB which creates a little wind resistance but I was getting 400km per tank before I installed it, so it made no difference.

I only have 110,625 miles on the clock, I am trying to think what I can replace but I have no idea, my brakes don't drag or anything. Engine Compression is good

When I put the 235/75's on mine Dad figured we needed to multiply the figure (in your case 12.5) x .104 which should bump you up to 13.8 mpg.

hmm, interesting, how did you come up with the .104 figure tho?

Maybe try a fuel system cleaning. Clean the injectors, fuel rail, replace filter.

Perhaps I will try another bottle of injector cleaner on my next oil change, any recommendations?
If I can get a solid 17mpg (mixed hwy city) I'll be a happy camper, I know you don't buy a Jeep for mileage but at 12-13mpg I'd rather be driving a big V8

bjoehandley said:

When I put the 235/75's on mine Dad figured we needed to multiply the figure (in your case 12.5) x .104 which should bump you up to 13.8 mpg.

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I thing that my be your prob em. there is 2" diff in tire hight with would slow down you odometer and case you fuel mileage to be lower then figures would show

I came up with the 2" figure considering that stock was 205/75/15.


Flash.

Something else to consider:

You most likely are not using all 20 Gallons of fuel. I have an '89 with a 20 Gallon tank. The most gas I have ever put into it was right about 18 gallons, and I think that was when I ran so low, I pulled over and had my mom bring me some more gas. It was cutting out and I wasn't sure I would make it to a station. I had a safe place to pull over and wait. I do not think an XJ would be driveable with 1-2 gallons of gas in the tank.

So, what I am saying is, unless you know exactly how much gas you used in those 250 miles, you will not have an accurate MPG calculation.

My typical re-fuel is once the light has been on for a bit and usually ends up being 16-17 Gallons. 250 miles over 16 gallons is a lot better than 250 miles over 20.

When the low fuel warning light comes on, it takes exactly 16 gallons (60 liters) to fill up the tank to the brim so that should help somewhat in the mpg (or km/liter) calculations.

Agreed, I will look this up the next time I fill up and base it on those specs.
But on average the low fuel light comes on at 7/8th's of a tank for me and thats when it rolls over 400km's (suggesting roughly 2.5 gallons of fuel left)

For the most part, I think my speedo seems accurate but there will be no way to know without GPS
I fill up as soon as the light comes on, don't want to risk burning my fuel pump

When my low fuel light comes on, I have to *work* to get 16 gallons in the tank .. topping it off very slowly for nearly a minute past the initial pump cutoff. I normally get about 14.5 in at a refill.

Yeah, you have to trickle the gas in slowly after the pump has cut off to add those last couple of gallons to brim the tank. It takes some patience and it's often the driver who's waiting behind you to use the pump who runs out of patience first.

I think new spark plugs and air filter would be the best thing for you.

To know exactly how much gas you burned, fill the tank til the pump cuts out, reset the trip meter and drive around for a while. Then, fill the tank completely full once again. The pump will tell you how much went in, and assuming it cut out at the same "fullness" as before this should be an accurate measure of how much fuel you used between fill-ups. I can usually work 18ish mpg city with the 5-speed.

I agree with jrock, i do the same thing fill until the pump stops, zero out the trip odometer, and drive around till i have to get gas an then i fill it an see how much i used. Then just divide the mileage driven by amount filled an i recently did mine an got 15mpg on spirited drivin mianly city on 88 heep with 5 speed puck goat tranny. Last time injectors were cleaned was a few months back, an i have a full 2.5" exhaust an short cold air intake with cone filter, new spark plugs an wires, new fuel filter an new 235-75-15. I also replaced my radiator so the engine dosent really heat to optimum temp, so i have been cruisin in slightly higher revs to keep the temp up.

if you have any weight over the rear wheels (tool box, spare parts) it will hurt yer mpg

cherokee89 said:

You most likely are not using all 20 Gallons of fuel. I have an '89 with a 20 Gallon tank. The most gas I have ever put into it was right about 18 gallons, and I think that was when I ran so low, I pulled over and had my mom bring me some more gas. It was cutting out and I wasn't sure I would make it to a station. I had a safe place to pull over and wait. I do not think an XJ would be driveable with 1-2 gallons of gas in the tank.

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I've put 19+ gallons in on more than one occasion. It's entirely possible....you just gotta be REAL easy in the turns (especially left) and pray for the best.

My Recommendations: Check the plugs. If they're worn out, replace the plugs, wires, cap and rotor (basically a full tune up). You might also run a good can of fuel injector cleaner through....I recommend Sea Foam. Only do one fuel injector cleaner PER oil change.

I dont see how haulin around a tool box would kill your milage. I've hauled much heavier before and had it not effect my results.

I also suffer from horrible mileage. I get sub 400km/tank. I'm running 205-70-r15 all season tires, go really easy on gas and keep the RPM's between 1500-2200 at most. I have new plugs, wires, fresh oil/filter, everything runs great the engine sounds like it's new, air filter is new, ran some injector cleaner through recently and none of that has made a difference in my MPG factors.

I don't mind paying a bit more for the luxery of driving an SUV, but since I'm only getting around 12MPG at most I may as well be driving a full size. I had a 78 mercury monarch with a 351 which I drove like a madman everywhere(it was my first car..) and I STILL got better mileage than the cherokee gets.

Also keep in mind that winter time means winter additives to the gasoline, and they usually result in a drop in milage.

Atleast here in the states they add crap to the gas....I would imagine the same goes where you are.