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

[Johnnie Walker]

Strokedjeep.com, bored TB's well worth the money.

And depending on the commute, "hwy" will differ from long distance hey mileage. SInce my commute is only about 14 miles one way My avg is lower than when I drive long distances.

 

[cdrake261]

Strokedjeep.com, bored TB's well worth the money.

And depending on the commute, "hwy" will differ from long distance hey mileage. SInce my commute is only about 14 miles one way My avg is lower than when I drive long distances.

I put 22.6 miles(iirc) from filling up to filling up again at the same station...99% of the drive is at 60mph on cruise, the 1% of in town driving is 45mph.

I have the infamous p1391 engine code, oddly still there after I replaced the crank and cam position sensors. Exhaust is rich in fume, and the idle is rough...going to replace ignition coil this weekend and inspect for shorting out wires. Still trying to figure it out...

 

[LYKOS]

If you decide to look for exhaust parts that aren't expensive AND are decent quality try http://performance-curve.com/. I bought m pre-cats, downstream cat and pipes from him. He treats you right and gives a discount.

For O2 sensors you are always better off going with the stock parts. That doesn't mean MOPAR it means stock parts. The stock O2 sensors on these Jeeps are NTK. I bought my replacement O2 sensors here http://www.rockauto.com/catalog/raframecatalog.php. The factory, never replaced O2 sensors were IDENTICAL to the NTK. By identical I mean they were NTK with the same part number on them.


I am in no way affiliated with the above vendors. Just throwing out a little cost saving advice based on my own experience.


I saw a four MPG drop in mine over the course of about six months. New tie rod ends, wheel hubs, u joints and ball joints later I got it back.

It all adds up...



FWIW I was having overheating issues too. New radiator, water pump, tstat etc later and I was still overheating. Replace cats and o2 sensors and the overheating went away.

Occams razor dictates that the simplest answer is most often the simplest. Occam didn't own a Jeep.

 

[jeepboy381]

I installed my overhead consol and that helped my mileage a little.

I installed new factory ntk oxygen sensors and that also helped a little. My XJ has 80,000 on it now and I believe the 02 sensors were factory.

Installed champion factory plugs and that changed nothing, previously I had ngk v powers that were worn. The jeep runs the same and no improvement.

I have not checked yet but believe I am getting 13-14 mpg now, up from 11 before!

This weekend I am installing a magnaflow muff, cutting the precats off and installing pipe in their place. I like cats but under my intake manifold in the engine bay is no place for them!

I have a trick for the secondary 02 sensors. Well see what happens...

 

[16vvincent]

I just read through your fuel economy thread just to see if anything was missed. I just had this happen to mine a couple of weeks ago. About the time that there was a big change in outside temp.
Check your coolant temp.
If your thermostat is sticking open, opening below 170 or missing, that will have a huge effect on your fuel economy.
I saw a big drop in mileage and was starting to wonder, when I looked at the temp gauge and saw it reading a little low. Now, not having driven Annie in the winter (just bought her over the summer) I was not sure what the gauge should have read. Put a non-contact thermometer on the upper rad hose and found it was reading 152 deg f.

Where this matters is the pcm will not go into closed loop until ECT above 170 deg or so. Open loop means good power, but crappy mileage.
Open loop also means that the pcm will look at the o2 sensors, but will not use them as a final checking value for mixture.

 

[Johnnie Walker]

I put 22.6 miles(iirc) from filling up to filling up again at the same station...99% of the drive is at 60mph on cruise, the 1% of in town driving is 45mph.

I have the infamous p1391 engine code, oddly still there after I replaced the crank and cam position sensors. Exhaust is rich in fume, and the idle is rough...going to replace ignition coil this weekend and inspect for shorting out wires. Still trying to figure it out...

Definitely should be doing better than 10mpg, but that short of a distance will not net you mpg as it would on a road trip. My last trip to Hollister Hills, averaged 17.5 mpg averaging a speed of 75mph

 

[srmitchell]

I think I'll install the new o2 sensors asap.

The lack of a dragging front axle has brought the mpg up a good amount, but I haven't measured it yet.

 

[heyhar]

One thing I've not seen in the entire thread is Coolant Temp Sensor. This and the O2 sensor(s), upstream, are the two main factors for attaining closed loop operation. As has been stated, the factory O2 sensors seem to make the vehicle happier.

I know it's a few bucks, but I have a Scan Gauge II in my '96. I have it set to read instant and average MPG, coolant temp., and voltage. There's also an option to make it monitor the open or closed loop operation, handy if that's what you're chasing.

I also have an UltraGauge, currently in our Outback. It displays eight different functions (as opposed to Scan Gauge's four), and it always shows loop operation. It's interesting to see how often the engine goes open or closed, depending on where the throttle is.

There is a way to test both the O2 and CTS, available somewhere here on . I've used them both in diagnosing my '96, leading me to replace both my four-year-old O2 sensor (it had become lazy, and wasn't a Mopar issue), and the original CTS, as it didn't work at all, thereby prohibiting closed loop operation. Replaced them both, and mileage, within a couple of tanks, was up to over 20 MPG highway (original sticker estimate is 16/19), on stock springs and 235/70 tires. Although, not a match to my '92, which gets 23 highway all day long. Not much friction left in a 200k motor, I guess!

 

[BlueCuda]

Since I started driving mine everyday again I have been halfass tracking mpg. I have a stroker with bigger injectors so my console reads 2 mpg high roughly. It is however a good indicator of how different driving effects mpg because it does accurately go up and down lol.

Idle time is the big killer for mine. If I stop at mcds for breakfast everyday it brings my average down a fair amount just from the extra idle time in the drive through.

It also doesn't like the highway at 75+ or anything above 70 really. It gets the best mpg in town with light traffic.

Also, as crazy as this sounds I put my spare tire and carrier back on and the mpg has been up some this week I don't know if it somehow helps with aero or what but its weird.

It also doesn't matter how I drove it really, if I baby the thing like crazy it's gets a marginal amount better than if I just drive it normal and get on it from time to time. In reality I flog the hell out of this thing a fair amount and it doesn't have much of an effect on mpg.

Combo 97xj 4.6, 5.5 lift, 4.56 gears, 35s, 4400lbs. It gets an average of 13-14mpg with mixed driving. I am confident it would get 15-16 if I were to ever drive it very far at 65-70, however when I do see highway time it's on a turnpike and I run 75-80mph.

 

[srmitchell]

Hey guys, still battling this. Went on a backroads trip this last weekend, filled the jeep to the brim, I mean FULL, and I only got 110 miles to the half way mark on the tank. I have driven another 50 miles, and it is now at 1/4 tank.

Gas is 4.19 a gallon here, I need relief lol.

Recent updates-
New brake caliper up front, (the old ones were sticking), new pads, turned rotors all around.

Bored the throttle body to 60mm.

Switched out my cowl snorkel setup for a possibly higher flowing opened up stock box.

NTK oxygen sensors at the two upstream locations.

Tires always inflated to about 35 psi. (high for my load E tires.)

It still gets 200, to maybe 220 a tank.

Any ideas?

Here's my stance right now, not too much lift, and no roof racks or tires on top.

Here's the air box-

The only other thing it could be is the MAP sensor.
Thanks guys.

 

[Tim_MN]

Miles per tank measures nothing, sorta like talking about peanuts per beer. The gas gauge is not calibrated, and the display is not linear. It only is a more or less gas indicator.

What are your miles per gallon, adjusted for tires/gears if necessary ? You should have multiple fill-ups calculated for mpg's to allow for changeable driving conditions and weather.

 

[GordoSmasho]

I think he is assuming everyone knows how many gallons a stock 01 tank holds. Even on the conservative side of 17gallons at fill up. 220 miles gives you 12.9 mpg. I'm at that same level right now so I feel you pain. I know I should be getting more like 15-17 avg. I daily drove on this exact setup for years and got that but for some reason in this jeep I'm suck at about 12

 

[XJsportG]

Have you changed your speedo gear? Or do you have an electronic one? I have 31s and 3.55 gears and my speedometer is 11% off could be another thing to think about?

 

[XJLI]

Miles per tank measures nothing, sorta like talking about peanuts per beer. The gas gauge is not calibrated, and the display is not linear. It only is a more or less gas indicator.

What are your miles per gallon, adjusted for tires/gears if necessary ? You should have multiple fill-ups calculated for mpg's to allow for changeable driving conditions and weather.

This. Fill the tank til it's overflowing from the filler neck. Reset your trip odo, drive til the gauge reads empty, then fill to the brim AGAIN. Divide miles driven by gallons filled.

Obv you need a correct speedo gear for this.

 

[srmitchell]

Fair enough. I know that's not the most accurate way to measure mpg, I just know that the gas gauge drops dramatically each time I drive.

Filling my tank is right around 75 bucks here, on my budget I don't usually fill it all the way.

 

[Rob Mayercik]

Did you ever check for leaks in the fuel lines?

I was getting terrible mileage (10-12) over the past year with my '92, but I didn't worry excessively about it at first since it isn't my DD. In October, though, I started getting a strong gas smell from the left rear area after short runs (but not on longer runs).

This spring, I had the truck up the local park to wind synthetic rope onto my new winch, and spotted a drip under the truck in that area. Got underneath, and discovered that the metal housing of my fuel filter had all the strength of a wet cereal box, and was leaking any time I turned on the key and pressurized - I'd been pumping gas out onto the ground every time I drove it.

Got a new filter on it, and am going to get it out for a short run this weekend (installed Bosch 703 injectors last weekend, need to get in a good shakedown around town before making a 100-mile drive for NACFest in a week and a half). I expect that I'll be seeing better mileage just from eliminating the leak.

You getting any raw gas smells when you run it?

 

[yossarian19]

Ever look at your MAP sensor?