My 01 xj is getting 10mpg... Help?

[995speed]

The coppers are not recommended for the 00-01 4.0. No distributor. It uses a waste spark system. (fires on combustion and exhaust to burn cleaner.) So the double platinum is recommended. I'm using Champion 7034's, double plat.

that's right! i completely forgot that they switched over to a coil over system

 

[98stocker]

4.56's with 35's and auto trans. I don't think I could get down to 10 mgp if I tried. Mine is always 15-16. I think there is something wrong with any 4.0 that gets 10, so I would keep looking...

 

[jeepboy381]

I have the same problem on an almost identical XJ. 2001, automatic, 33x12.5 tires, 4.88 gears, bumpers winch sliders. I have stock exhaust and intake and the engine is also all factory. I also have the California emmisions package, " 3 cats and 4 oxygen sensors". My jeep only has 70,000 miles on it, spark plugs are Bosch platinum and are new, I have not changed the o2 sensors yet. I even run 5w40 rotela synthetic motor oil and synthetic oil in my diffs.

It has always got 10-12 miles per gallon but has always been pushing 33's. I can drive the shit out of it or drive like a blind deaf old man, my mileage is always the same.

My old 87 xj built the same with a stick shift but on 35" tires would get 18 mpg or better.

I would kill for better mileage on this turd.

 

[jeepboy381]

You may disagree, but here are 2 examples for you. I own both these vehicles.

01 XJ,4.0L lifted 5 inches. All stock engine except no mech fan, 4.56 gears, auto, and 33X12.5X15 ATs= 15 MPG Hwy, 12 city.

06 LJ 4.0L, lifted 4". All stock engine and drivetrain, 3.73 gears (stock), manual, an 33X12.5X15 ATs, 19mpg Hwy, 15 city.

The LJ is literally a brick going down the road, atleast the XJ has some aerodynamics. Same engine, same curb weight, same wheel base, different gears, same tires. The major difference I see here are the gears.

Every single RPM vs Gearing chart I have seen points to 4.56's not being reasonable if you are looking for MPG.

The big difference here is not gears, it's auto vs manual.

 

[TheCodeMonk]

I have the same problem on an almost identical XJ. 2001, automatic, 33x12.5 tires, 4.88 gears, bumpers winch sliders. I have stock exhaust and intake and the engine is also all factory. I also have the California emmisions package, " 3 cats and 4 oxygen sensors". My jeep only has 70,000 miles on it, spark plugs are Bosch platinum and are new, I have not changed the o2 sensors yet. I even run 5w40 rotela synthetic motor oil and synthetic oil in my diffs.

It has always got 10-12 miles per gallon but has always been pushing 33's. I can drive the shit out of it or drive like a blind deaf old man, my mileage is always the same.

My old 87 xj built the same with a stick shift but on 35" tires would get 18 mpg or better.

I would kill for better mileage on this turd.

Mine does a consistent 15 mpg hwy and city both with the 33's. (Stock geared auto) Granted, i have significantly less weight (no rear bumper or skids/sliders installed yet).

I am keeping an eye on this thread so I know what to do to get better once I've added all the weight back on. Definitely would prefer not to go much below 15.

 

[muduck18]

Any suggestions? Is the fuel filter/sock thing worth changing? Maybe the timing chain? The cat? I've got a lot of armor on this jeep, but the numbers just don't add up.

Thanks!

Coumbus

I know guys have talked about it already, but I wonder what RPM's are you running at 60/65?

Does your transmission ever drop all the way into OD locked?

My dad has a Completely stock XJ and has ALWAYS had issues with low mpg. and he drives slow, like 55-60 all the time. Out of normal cars he can get way more the mfg claims. but the XJ is terrible.
But I drive like a bat out of hell, and I get 17-19 out of my 3" lifted 32's and 3.55 gears on an ax15.

so to me is sounds very much transmission or maybe transmission/tires?

Have a buddy with any stock tires? check your rolling resistance. get up to a speed 65/70 (use a GPS for accuracy) drop it in neutral and see how long it takes to slow down to stop.
Switch tires to a stock set, or even a less aggressive tread of the same size.
and repeat the process. obviously on the exact same stretch of road.


There are so many things that affect the mileage of any vehicle and sometimes its stupid what can cause it low mileage.

Case and point. I have an '07 Subaru Impreza. (again I drive like bat out of hell) but I average 25mpg during the winter and 23 during the summer. For the longest time I ran with out AC to try to combat that lower milage.. but what I found out was that running with the windows open caused more rolling resistance and drag than the AC caused in power loss. in the winter I can now bump the mpg's up to 27mpg by running the heat on floor instead of defrost. and in the summer I can average a steady 25mpg by closing the windows and running the ac.

All those things you listed that are changes to your vehicle might just be working together to cause the low milage. where others have similar setups but one or two little things different.

 

[WB9YZU]

The big difference here is not gears, it's auto vs manual.

City yes.

But on the HWY the TC is locked on a AW4 and the OD ratios are pretty close between the AW4 and the NSG370 (.74 AW4 VS .84 NSG370).

Besides, I have owned a number of XJs with 3-5.5" of lift, with a combination of gears and tires, all on the high geared side vs the tires. (3.07, Manual, 30"=20mpg) (3.55, Auto, 31"=18mpg)(3.73, Manual, 2.8L, 31's=19mpg).

So there is a history there.

There is a reason the Big 3 are not building trucks with 4.56 axle ratios and modify old tech engines to put out more power, they can't meet CAFE standards with that plan.

And we can't either...

 

[Westernhunter]

So how do you know when the TC is locked? My 2001 always seems a little sluggish. I am also on 33" tires with 4;56 gears. All stock engine.

 

[Tim_MN]

The 00 has 5.5" of lift, both sets of tires are 31's, and it still has 3.55 gears. I don't notice much of an mpg difference between the Mt's and the At's. I switch over tires every fall/spring. I have the OHC with trip computer. I get 15-17 city/hwy and 17-19 all hwy (but not faster that 63-65 mph).

I use AutoLite APP-985 platinums in the 00-01's and NTK or genuine Jeep O2 sensors. Some people claim Bosch O2 and Jeeps are not happy together.

 

[chris420]

I thought the largest tank our Jeeps have is 18 gallons? My Jeep gets 15mpg average.

 

[Pelican]

What is your point about an 18 gallon tank? The size of the tank should not affect the mpg to any practical degree.

I'm not sure about the last couple of years but all previous XJs came with either a 13 gallon or 20 gallon tank. However, the physical size of the tank was the same 20 gallons. The advertised 13 gal capacity was achieved by artificially limiting the fill capacity.

 

[Westernhunter]

What was the point of that?^

 

[Pelican]

Who dat say who dat....

If you are referring to my post, I was responding to the statement about 18 gal tanks. Did I miss something?

 

[Westernhunter]

No, why would Jeep make the same size tank but different capacitys?

 

[Pelican]

There have been threads on this subject from time to time, one not too long ago. I don't know if anyone knows for sure but I think it was just a marketing feature.

The sticker on my '85 basic equipment included Fuel Tank 13.5 Gallon
Then under Optional Equipment: Extra capacity Fuel Tank $49.00

This doesn't prove that the physical size of the tank was the same but it is well established that it was/is.

 

[srmitchell]

I have the same problem on an almost identical XJ. 2001, automatic, 33x12.5 tires, 4.88 gears, bumpers winch sliders. I have stock exhaust and intake and the engine is also all factory. I also have the California emmisions package, " 3 cats and 4 oxygen sensors". My jeep only has 70,000 miles on it, spark plugs are Bosch platinum and are new, I have not changed the o2 sensors yet. I even run 5w40 rotela synthetic motor oil and synthetic oil in my diffs.

It has always got 10-12 miles per gallon but has always been pushing 33's. I can drive the shit out of it or drive like a blind deaf old man, my mileage is always the same.

My old 87 xj built the same with a stick shift but on 35" tires would get 18 mpg or better.

I would kill for better mileage on this turd.

I also run rotella 5w40. I just don't get it.

This jeep should get better mpg. It has TONS of power too. Torque is great, and the tranny shifts great. The torque converter always locks properly.

Rpm's are 2250 at 65.

Things I want to investigate
-O2 sensors
-Timing Chain
-Catalytic Converter
-Intake options

 

[jeepboy381]

I think it is my pre cats. I get bad heat soak, even when it is 50 degrees outside! It has progressively got worse, heat soak was rarely an issue a year ago even when it was 90. Those cats are getting hotter, maybe they are clogging up.

My power is still fine though.

 

[WB9YZU]

I thought the largest tank our Jeeps have is 18 gallons? My Jeep gets 15mpg average.

The newer ones have 20 gal tanks.

That however is totally irrelevant to the discussion as MPG is calculated over a few fill-ups at the same pump at the same station and is the miles traveled since the last fill divided by the amount of fuel put back into what was a full tank.

Ideally...

But we all know that in real life, people simply take down the miles traveled and divide it by what they put in the tank. MPG can fluctuate a a fair amount depending on the accuracy of the pump and the orientation of the slab the Jeep is on, but it get's you an idea of what is going on.

 

[muduck18]

Things I want to investigate
-O2 sensors
-Timing Chain
-Catalytic Converters
-Intake options

yeah, having three Cats' might get expensive to replace, but its definitely suspect.

I think I would try the rolling resistance first. From the sounds of it you have the engine well maintained and performing well, which leads me more to something else, like weight, or drag, etc.

 

[Breezio69]

Here is some love for all you lifted jeep horrible gas mileage sums a .....es.... assuming you fill your tank up per week, @$50 a tank, you are spending $3700 a year to drive the pos... to get a whopping 10-15mpg. Do yourself a favor and buy a new car on the side... hell, find beater that gets 25-30mpg and have it pay its self off in 4-5 months, save the jeep for the bad weather or camping trips...

Just sayin, anything besides going stock is going to waste your time and money and still get horrible gas mileage by today's standards.