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-   -   Fuel mileage took a big dive!!!! (http://www.wranglerforum.com/f282/fuel-mileage-took-a-big-dive-145420.html)

Moparnut 03-10-2012 08:27 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

ebigham1 03-10-2012 09:38 AM

It could be an o2 sensor but that should throw a code.

Jerry Bransford 03-10-2012 09:43 AM

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.

Alaska TJ 03-10-2012 11:48 AM

Is there a test for bad oxygen sensors?

div4gold 03-10-2012 11:54 AM

Notice any loss of power with the decrease in mileage?

Moparnut 03-12-2012 08:24 AM

no loss of power. I just keep track of my fuel mileage and noticed this huge drop.

s3nt3nc3d 03-12-2012 09:00 AM

Quote:

Originally Posted by Alaska TJ (Post 2125040)
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 yeah...as 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...

SinfulDragon 03-12-2012 09:55 AM

and at around $50 each (2 down and 2 up correct?) you'll really want to know what ones to start with

jamesbdunn 08-21-2013 12:20 PM

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?

MichTJ 08-21-2013 08:18 PM

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!

ArthurTJ04 08-21-2013 08:50 PM

Quote:

Originally Posted by Jerry Bransford (Post 2124746)
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??

Apoc1528 08-21-2013 10:04 PM

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.

Verf 08-21-2013 10:30 PM

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....


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