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Replace 02 sensor or tune up?

CJ96xj

NAXJA Forum User
Location
Bel Air, MD
I want to increase mpg, and do reg. maintenance and have 50 bucks to do so, what is better to replace, the 02 sensor and which one or should I change plugs, wires,and cap? The air filter has 200 mi on it. Thanks
 
What are you getting now? How did you calculate it? What mods do you have?
 
I am getting 13-14.5 mpg with 235/70/r16 BFG AT's and rock slider bumper. It was actually worse before the tires, around 12-13.
I calculated it by filling up, reset trip odo. fill and divide miles driven by gallons put in at the same pump.
Here are the mods
168353_1796871607435_1409075676_1980676_5359136_n.jpg
 
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02 sensor will not help your gas milage unless it is giving a false or bad reading.

Id do the tune up with MOPAR OEM stuff and champion coper plugs as stated earlier.

And watch how you drive!

I drive 104 miles everyday on the highway. With a stock XJ i can get 19.72 mpg if I really drive conservatively, but it will drop to 16.5 when I do 80 to 85 the whole way.
 
A can of BG44K will remove carbon and clean the injectors. For $20 it is probably going to give you the biggest boost. I would follow that with a new air filter, an oil change with a good synthetic oil. New spark plugs if they have 30k+. Go with cheap Champion plugs, copper preferrably. They work the best. Forget the multiple electrode plugs.
 
BASICS, always, please.

Champion copper plugs, cap with brass not alloy contacts, rotor, plug wires.

Yes, a bad/weak/failing o2 sensor can kill your mileage, and it can do it without ever throwing a code. How many miles since it was last changed? Good for about 80k miles on your year.

Poor belt driven accessories can kill your mileage too, long before you will know they are going out.

JP Magazine has a three-part series on XJ mileage. Mileage Master

http://www.jpmagazine.com/projectbuild/154_0808_building_a_fuel_efficient_jeep/index.html

http://www.jpmagazine.com/projectbuild/154_0810_building_a_fuel_efficient_jeep_part_2/index.html

http://www.jpmagazine.com/projectbu...cherokee_xj_project_mileage_master/index.html
 
Is your odo correct? Figuring mileage with inaccurate readings will make it look like you're getting worse than you are.
 
I am a bit surprised at all the answers here so far. I think the answer depends on age and condition of all the parts. I use Autolite single platinum tip plugs on both my gas jeeps, 87 and 89, and the 89 gets 20-24 mpg, so I don't buy the special old style plugs story for 4.0's.

I would look at age and condition, and test the O2 sensor before making that decision, but my 89 was getting 20 mpg average with a nearly bad, well worn cap, a year old, 25,000 mile, used air filter...and so on.

Based on the mileage he posted, he should check the O2 sensor, and while he is at it check the CTS and MAT sensors for hot and cold resistance readings.

I would also be curious to know if he has any other problems besides MPG drop.

Check the Cap for signs of wear for sure!!!! Check the air filter for lots of dirt and or oil. Pull the spark plugs and inspect them for condition and gap, and test the pre cat O2 sensor per instructions in the O2 sensor test threads in this forum.

Based on his 12-13 mpg post, my money is on a bad O2 sensor.
 
Tune up first. Champion plugs, the best wires you can find/afford. BG44k in the tank, new fuel filter, Mopar Decarb Spray (avail at dealer) spray can thru throttle body at idle, turn off, sit for 15 minutes, start engine, smokes like a freight train and cleans all the valve, pistons, chambers, etc:, good stuff..., make sure tranny is in good shape (no slipping), fresh fluid, etc: synthetic fluids front to rear (diffs). tire pressure set to proper levels. change oil and use something like 5w-30 or 0w-40 synthetic..

Maybe have a lazy O2 sensor, this can be verified with a scanner or volt meter.. For the price of a O2 sensor I would check it before replaceing it. If it is lazy then yes replace the O2 sensor..
Also check for plugged exhaust system, If the system is plugging up then milage will go to crap and nothing stated sofar will change anything.
just suggestions... all i can think of right now..
 
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