Gas Consumption Record - 6mpg

Ok, I've been doing a couple tests lately and my mileage just plain SUCKS. What I have done is wait for the gas light to come on and stay on (roughly 1/8th of a tank left) and then add 20L of fuel

Reset the trip and see how long it lasts me, from my last couple tries I get a range of about 60-70km's on 20L of fuel before the light comes on and stays on, which is equivilent to 6mpg....

Now I don't know what is wrong with my Heep but she ain't right...I would expect 6mpg turning 35's on stock gears

What I am running:
235/75/15's stock gears, auto, 4L np242. Jeep is 100% stock (1996)

I have an amsoil air filter on order, it's been back ordered along with my amsoil engine oil. My tire beads leak, I have had them reseated twice and the same bullshit, so I just keep an eye on my tire pressure...I drive like a little girl and I don't get how this all adds up.

The 4L purrs like a kitten, no hesitation, no problems, no codes being thrown...I just don't get what is going on?

Is there a full ignition tune up kit I can buy? Or specific brands I should run? Exploring my options and something has to get done and fast. I know that there is a hole in my muffler that I caused from going off road, however I can't see that causing such a huge issue...regardless that is going to be fixed asap as well.

Well those aren't stock tires. Stock for your year will either be 225 75 15 or 215 75 15......so your speedo gear isn't on 100%.

Also, as for the tires - have a shop grind down the beads and reseal them. 2 of my wheel beads were leaking and they clened the beads and resealed them, no leaks since.

When's the last time your sparkplugs, distributor cap and rotor have been changed? Wires? Worth doing.......how about fuel filter? What temp is your Jeep running at? Run some seafoam through the oil and vacuum.....also try some injector cleaner through the fuel, or use another can of seafoam in the fuel for this purpose as well.

The very first thing, at 6mpg, I'd go over the fuel lines with a microscope and look for leaks. At 6mpg it almost sounds like it's not coming out of cold loop, check to see if your cat is glowing red, they do that with too rich/cold loop after an extended period.
Step 1 check your tire pressure, I run my BFG AT/KO's at around 35-40psi.
Step 2 Do a tune up, use stock OEM chrysler/jeep parts for a baseline, champion plugs too, nothing fancy, the fancy ones cause too many problems.
Step 3 Run a bottle or two of Chevron Techron FUEL SYSTEM cleaner, not FI cleaner, 20oz bottle.
Step 4 smell your oil, is there a strong gas smell ? You could have a dribbling injector.
My 98 gets 18-22mpg.

1. I run the 235/75/15's are 35psi
2. Regards to a tune up, yes I will be doing one ASAP
3. I have ran a bottle of FI cleaner but that was a while ago, I'll look at my local Canadian Tire for Fuel System cleaner (similar to Auto Zone, if you guys have it there I should have it at my crappy tire) - I know I can get Seafoam so maybe I'll have to give it a shot.
4. Oil doesn't give off any strong smell/sign of gas, it is however almost due for a change.
5. I've been underneath her recently, what does need fixing is the muffler, as it's beginning to separate at the rear seam (damn off roading )
6. No fuel rail leaks from what I can see although gas does evaporate, my vehicle is garaged and it doesn't smell like raw fuel after it's been parked for a while.

Hmm what else, it doesn't run constantly at 210 (100 for me), runs in the 80-90 degree area most of the time, as well when we were safeting my Jeep, I had a water pump leak, my buddy thought it was my rad, so he tried taking the fan shroud off and snapped it into 3 pieces. Should I find one to replace it? Although I don't see how that would make a difference regards to over cooling, that would be overheating...when we changed the water pump out we also put in 2 new 195 Tstats.

J-Roc said:

1. I run the 235/75/15's are 35psi
2. Regards to a tune up, yes I will be doing one ASAP
3. I have ran a bottle of FI cleaner but that was a while ago, I'll look at my local Canadian Tire for Fuel System cleaner (similar to Auto Zone, if you guys have it there I should have it at my crappy tire) - I know I can get Seafoam so maybe I'll have to give it a shot.
4. Oil doesn't give off any strong smell/sign of gas, it is however almost due for a change.
5. I've been underneath her recently, what does need fixing is the muffler, as it's beginning to separate at the rear seam (damn off roading )
6. No fuel rail leaks from what I can see although gas does evaporate, my vehicle is garaged and it doesn't smell like raw fuel after it's been parked for a while.

Hmm what else, it doesn't run constantly at 210 (100 for me), runs in the 80-90 degree area most of the time, as well when we were safeting my Jeep, I had a water pump leak, my buddy thought it was my rad, so he tried taking the fan shroud off and snapped it into 3 pieces. Should I find one to replace it? Although I don't see how that would make a difference regards to over cooling, that would be overheating...when we changed the water pump out we also put in 2 new 195 Tstats.

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My son did a tune up on his 'new to him' 97TJ, I think they were the original plugs, wires, cap, rotor with 90K on it. It ran 200% better afterwards. The other biggie that can really cause milage issues is the O2 sensor, the one by the header. He replaced both on his, upstream and downstream, the downstream was triggering CE every once in a while.

Stock thermostats are 195'

Back to the origional poster - what do you mean you installed 2 new thermostats?

Your jeep should be running at around 210. If you're running at about 100 degrees you must surely be in closed loop.......I'd check your coolant temp sensor. Also an oxygen sensor replacement probably wouldn't hurt if it's the origional.

Leo Brazil said:

I have a XJ 98 4.0L auto. with 235/75/15 at 33 PSI always
The best MPG I can get is 12 city - 15 highway...

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Wow, I get 15.5mpg with 35's and 5.13's highway doing like 75mph all the time. Something seriously wrong with your jeep.....or your gas....

53guy said:

Wow, I get 15.5mpg with 35's and 5.13's highway doing like 75mph all the time. Something seriously wrong with your jeep.....or your gas....

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He may also want to check his unit conversions. He's likely going from a l/100Km measurement to MPG, but a US gallon is roughly 3.8 litres vs. approximately 4.2 litres for an Imperial gallon.

I get around 18-19 combined highway and city, average of 70-75mph on the highway, with no cruise control.

My trick is to not jack rabbit off the line when in the city (dont usually run it over 2500 rpm's), keep it tuned up, and run good quality gas in (read: not premium, but regular unleaded bought from a good station). I find that I get my best milage off of BP regular, so I don't mind paying a couple of cents more to get theirs over another.

I run mid grade fuel (89), I changed out the Tstat twice thinking first one was bad but she doesn't run at 210F (100C degrees is my equivilent for those who are wondering, I would estimate I run around 80C degrees, thats probably like 160-170F). Also I convert all my fuel mileage to US Gallons to avoid confusing others on the board. And like I said before I drive like a bitch 2000rpm no more

Edit:
Um something else just came to mind that I completely forgot about... I put redline water wetter in my rad when I redid my pump because I was worried about over heating from not running a fan shroud. I originally thought it was a money grabber but that shit really works. Would you suggest I flush out my system? So that I run at optimum temp? The ODD times I have had my jeep over heat and the e fan kicked in, but it hasn't done it for a while... Still waiting for it to warm up a shit load to see if she'll actually overheat enough for the electric fan to cool it down.

Both the cold operation and the low gas mileage sounds like O2 sensor problems, bad :twak: O2 sensors! They make the computer make the engine run rich (or colder, less heat produced by burning excess fuel), so you get both miserable gas mileage as well as lower coolant temperature.

With that kind of gas mileage, change the O2 sensors before you do anything. Then if needed follow with new cap, rotor, plugs, etc.

Lastly I come up with 8.23 MPG using 70 Km and 20 l, and converting to US gallons. That is about what I was getting in cold weather, with 10 minute daily warm ups in the driveway in the winter combined with city driving, before I replaced the O2 sensor. I was lucky to get 11 to 12 highway.

I am getting about 10 mpg now with straight stop and go, local 30 mph spped limit, stop sign every block and heavy traffic driving, and about 18 mpg on the open highway when I can find one:rattle:.

I have a fan shroud, let me know if you'd like to buy it....It's been trimmed so there will be no problem getting it in with the fan and fan clutch already on the vehicle....

Also how about coolant temp sensor? If the oxygen sensor isn't you're problem, that's where I'd look next.

Water Wetter wouldn't cool that much....maybe 10 degrees maximum!

Blaine, I'm looking into costs for O2 sensors right now... with a 96' I will have an up stream and down stream sensor correct? Damn 2x the price HAHAHA, oh well it's either suck it up now or suck it up at the pumps if it doesn't work.

Seems like a process of elimination unfortunately...
Also Blaine thanks for the offer on the shroud, I'll think about it for sure, but I might convert to a dual AC fan setup not sure at the moment. Really depends if my jeep starts having over heating problems. We are just coming out of our crap weather phase here in Igloo land so things might start to look up.

I just filled up my gas tank to the tits tonight, I'll let you know what I put on the old clock, praying for over 300km's (188 miles) on a 20 gallon!....

They I'll reassess the problem.

So far the list:
1.O2 Sensors
2. Cap, Rotor, Plugs, Wires (do red ones make more horsepower?), Distributor
3. Can of Seafoam in the gas tank
4. Air Filter

Thats like $300 worth of shit there! Postponing my lift kit even further!

The o2 sensor after the catylitic converter doesn't affect the fuel/oxygen ratio.......it's only there to double check that your catylitic converter is working and such.

The o2 sensor that controls the fuel/oxygen ratio is the one on the downpipe.

Just some information.......you may want to do both anyway since you'll be renting the o2 sensor sockets (unless you already own them) but I'm just telling ya.

Make sure your coolant return line to the resivoir is tied out of the way of the mechanical fan blades if you aren't running a shroud. Don't want that hose getting mangled for sure!

Color of spark plug wires is just that.....different color.

Silicone wires are the best.

Also perhaps make sure the distributor cap you are buying has brass terminals. It won't corrode nearly as fast as the distributor caps with aluminum terminals.

As for plugs, get Champion Copper plus plugs.......I believe they are RC12LYC, as I believe that is listed on the white information card on the firewall.

Hehe I was just joking about the wires, I forgot to add a smiley for that red plug wire hp rice comment.

Yea when buddy busted the shroud I ziptied the lines to the front clip, first thing that ran through my mind. Thanks for the part number on the Champion plugs, was searching for that in the afternoon

3 of my buddies are graduating this year from Automotive power programs, im sure one of the fawkers has a O2 socket. Is there any particular reason why an adjustable wouldn't do the trick? Or any open end wrench for that matter? We don't have a rent-a-tool sort of deal down here to my knowledge...

casm said:

He may also want to check his unit conversions. He's likely going from a l/100Km measurement to MPG, but a US gallon is roughly 3.8 litres vs. approximately 4.2 litres for an Imperial gallon.

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I'm pretty sure about my convertions. We use here KPL or Km/l. l/100Km is used in Europe.
To get my conversion I used US gallon = 3.8 liters and 1 mile = 1.6 Km
As my orginal "mileage" is 5Km/liter I'm getting only 11.875 MPG, no doubt it's pretty bad for me....

J-Roc said:

I run mid grade fuel (89), I changed out the Tstat twice thinking first one was bad but she doesn't run at 210F (100C degrees is my equivilent for those who are wondering, I would estimate I run around 80C degrees, thats probably like 160-170F). Also I convert all my fuel mileage to US Gallons to avoid confusing others on the board. And like I said before I drive like a bitch 2000rpm no more.

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Same situation for me down here....but better saying I'm driving like an old lady....lol...
My XJ 98 is Canadian according to it's serial number.

Just for laughs, put some cardboard in front of the radiator, try different sizes till you get the right sq inches to make it run about 20+ degrees hotter. If your gas milage goes up then thats the culprit. It's weird though, I just can not see how a missing fan shroud, new tstat and waterwetter can overcool. If anything the missing fan shroud should warm it up a bit by not pulling air evenly over the fins. I wonder if your temp sender is reporting the wrong temp to the ECU.. Is you heat and everything else good ? maybe use a temperature gun to check the block temp and a few other points.

Leo Brazil said:

I'm pretty sure about my convertions. We use here KPL or Km/l. l/100Km is used in Europe.
To get my conversion I used US gallon = 3.8 liters and 1 mile = 1.6 Km
As my orginal "mileage" is 5Km/liter I'm getting only 11.875 MPG, no doubt it's pretty bad for me....



Same situation for me down here....but better saying I'm driving like an old lady....lol...
My XJ 98 is Canadian according to it's serial number.

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I thought you all down there in brazil were running much higher ethanol levels then 10 or 15 percent, thought you were all mostly 85% and above... with some running on pure alky..

I thought about carb boarding the rad but we'll see. I have 112500 miles on the clock... I'll bet dollars to donuts the O2 sensors are original unless they put new ones in when my exhaust was replaced in 2002. I have no proof to tell though. As well my heater seems to be working just fine but when it's in use it makes my temps drop even lower and the needle will sit just a hair above the first 1/4 mark