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Topic Review (Newest First)
08-21-2013 11:30 PM
Verf I love Rock Auto. I wish they had combo deals. Not price saving combo deals per se, but sanity combos. If I'm going to replace my O2 sensors, and they are going to be NTK's, why can't they all be next to each other so I know I'm getting the right ones or not? Or better yet, a button with everything you need, just waiting to be clicked....
08-21-2013 11:04 PM
Apoc1528 Hmm funny. I was going to post something similar. 2005 LJ with the 4.0. Big loss in mileage recently as well. Went from about 230-240 miles to about 180-200 a tank. 33in tires with stock 3.73 gears. Looks like I have an idea where to start looking now.
08-21-2013 09:50 PM
Originally Posted by Jerry Bransford View Post
My bet is on a bad 02 sensor. When they go bad, they affect the air-fuel ratio which can wreck your mpg and your power. 02 sensors have a limited life span and eventually have to be replaced. A bad 02 sensor will not necessary throw a code.
whats the life span on the o2 sensor??
08-21-2013 09:18 PM
MichTJ Spent $70/ea for oxygen sensors for my 1999 TJ 4.0. Replaced both for 150 out the door.

Yes a bad cat will effect mpg and burn up valves. If it sounds like crumbled glass then the honeycomb inside is cracked and done for. Replacement cat on Rock Auto set me back $140, came with the front pipe too though... Sounds like you need it!
08-21-2013 01:20 PM
jamesbdunn Will a bad catalytic converter effect mpg? i.e. excessive back pressure.

Is the cat swollen, does it sound like crumbled glass inside when you tap it?
03-12-2012 10:55 AM
SinfulDragon and at around $50 each (2 down and 2 up correct?) you'll really want to know what ones to start with
03-12-2012 10:00 AM
Originally Posted by Alaska TJ View Post
Is there a test for bad oxygen sensors?
You can check the voltage on them...a good working O2 sensor will flip flop voltages from like .1 to .9 or something like that. A lazy one will flip flop from like .1 to .3 or something. I'm just tossing numbers out...but far as I know, checking the voltages is the only way to test them. I'd just replace them if you've got a lot of miles on the Jeep and consider it preventative maintenance...while hoping that fixes your problem.

If I remember right, I think the downstream ones are the ones responsible for killing fuel mileage. Or maybe it's the other way around...crap...
03-12-2012 09:24 AM
Moparnut no loss of power. I just keep track of my fuel mileage and noticed this huge drop.
03-10-2012 12:54 PM
div4gold Notice any loss of power with the decrease in mileage?
03-10-2012 12:48 PM
Alaska TJ Is there a test for bad oxygen sensors?
03-10-2012 10:43 AM
Jerry Bransford My bet is on a bad 02 sensor. When they go bad, they affect the air-fuel ratio which can wreck your mpg and your power. 02 sensors have a limited life span and eventually have to be replaced. A bad 02 sensor will not necessary throw a code.
03-10-2012 10:38 AM
ebigham1 It could be an o2 sensor but that should throw a code.
03-10-2012 09:27 AM
Fuel mileage took a big dive!!!!

I have a 2005 Jeep TJ Sport. Automatic trans. 150,000 kilometers (90,000 miles) I live in Canada eh
My fuel mileage went from 400 kilometers / tank to 225 kilometers per tank.
I change oil on regular basis and maintain regular. No engine lights on and even checked with the OBD2 reader.

Cleaned airfilter, and throttle body

I am going to change the plugs but can't see that making that big of difference in the mileage.

Any additional help appreciated.

Thanks in advance

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