Haha. I completely understand. Well what is the best way to check how one is bad or not??

 

and ppl can calculate and speculate about their mpg's...u relle wanna no, run it dry, dump in a gallon and see how far u go

 

And is there any diagnostics that you must run for the computer in the jeep to accept the new O2 sensor? Or is it just a plug and play kinda deal?

 

might have to reset the ecu...idk if it will reprogram or not

 

I have 32's and the speedometer reads about 6 mph lower then what I'm actually going. Which means with bigger tires the odometer has less miles then you have actually traveled. So yes, there is a direct correlation between the odometer and tire size. If you do the math without a the right speedo gear to match your tire size, your getting better mpg then calculated. My jeep stock would get about 20-21 city completely stock... Now lifted 4.5 inches with 32's it gets around 16-18 mpg city.

Plug and play. Take the old one out, and put the new one in and your golden!

 

You only have to reset the computer if there is a check engine light.

 

i just know on some vehicles, even changing a battery will throw the ecu and make it run like crap until it can reset itself

 

Or....

Fill it all the way up. Before driving reset the trip odometer.

Next fill up check to see how many miles you went via the odometer, and compare to the amount of fuel the truck needed to get full with the miles you drove.

Divide the total miles driven by the gallons of fuel you needed. MPGs the easy, and smart way....no running outta fuel or any other inconvenience.

 

That reminds me of a friend who has a '70 Cuda we built years ago with a heavily massaged stroker motor in it-- a low 11 second street car. When anyone asks him about gas mileage, he tells them "it doesn't get gas mileage- it gets gas footage".

 

but all that extra fuel is just dead weight!

 

Once the ecu is reset, it won't run at it's best performance until the computer "learns" after 30 or so start cycles. However once reset the ecu has a base program that should run the engine just fine until it goes through the learning process. The only reason the ecu would be affected by the battery is if it's running on a low voltage or shorted out battery. Ive seen vehicles do some strange things with a bad or low voltage battery. All the sensors run on a basis of 5 volts, if the battery is low, or bad then the voltage would be lower obviously causing some problems there. Some vehicles are more sensitive to resets then others, the Cherokee however can be reset and run just fine afterwords if there is no problems with the engine, or it's control systems.

 

True. I recently had a problem where my underhood light came loose from the mounting bracket and stayed on for a couple days completely killing my battery. I jumped the vehicle, got it started and it wouldn't even idle until the alternator charged the battery back up. I also noticed my gas mileage wasn't as good for the 1st tank or so. Now that it's been through a good number of run cycles, it's acting normally again.

 

'97, 4.0, AW4, 231, 3.55 gears, 33x12.50 Kumho KL71s on black steelies, Yakima roof rack... 14-15 city, 16-18 hwy. And I go REALLY easy on it. I just swapped in a '99 intake, 703 injectors and some silly whistling TB spacer I got for free, so we'll see if that makes any difference.

 

 

One gallon of gasoline weights 6 lbs. 20 gallons of gasoline = 120 lbs. I don't know about you but I carry more weight in crap in the Jeep. If it was a 50 or 100 gallon fuel cell I could see a full tank adversely affecting your MPG....but not 15-20 gallon tanks.

Think about this. Less fuel = more trips to the station = more wasted fuel driving there, stopping, idling, waiting on a pump, etc. With a tank of fuel you constantly use that fuel so the vehicle is constantly losing weight in theory getting better fuel economy. It all averages out though. Fuller tank = less trips to the fuel station. That saves fuel my friend.