When to replace O2 Sensors? - JeepForum.com
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post #1 of 11 Old 12-01-2019, 01:01 AM Thread Starter
TwoThousandWJ
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When to replace O2 Sensors?

I have a 2000 Selec-Trac 4.0 WJ with 160k miles and my fuel economy is slightly worse than it was many years ago. I'm averaging 15 mpg with very little freeway driving (most days I don't drive on the freeway at all). I think I should be getting around 17 mpg as I was in the past although with more freeway driving. Jeep has remained stock the entire time, same stock tire size. The fuel filter and O2 sensors have never been replaced. Should they be replaced after 20 years and 160k miles? Regularly changed oil with full synthetic 5w-30. Champion copper core plugs replaced about 25k miles ago. Injectors also replaced around same time. Engine idles smooth, no fault codes. Tires running about 40 psi. In 2wd 99.9% of the time. All other fluids changed regularly. Brake line fluid replaced every 2 years. Brakes don't appear to be dragging.

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post #2 of 11 Old 12-01-2019, 09:33 AM
JoMc67
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I also have a 99' WJ 4.0 Selec-Trac and use to get 21-23 HWY, and 16-17 City...I'm now only getting around 18-19 MPG Highway, but at least still the 16-17 City...Just Installed SuperChips, K&N Intake, iridian plugs, new Mopar 02 sensors, all around same time this year, but nothing has changed (other then the WJ feels much better to drive).


I wonder if it had anything to do with my Rear-end Calipers ceasing/heating-up earlier this year (possibly damaging something)...So, I replaced both rear Rotors, Calibers, Brakes, but didn't effect mileage.


I think also have a slow engine leak (possible compression issue), and a slow Transfer-Case leak that might contribute to MPG Loss.
Maybe I should replace the Fuel Filter, and Rear-End Hubs next to see if anything changes...I don't know at this point ?


Joe
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post #3 of 11 Old 12-01-2019, 10:19 AM
CJ7-Tim
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1996 and newer OBDII-equipped vehicles, the recommended replacement interval for O2 sensors is 100,000 miles. They may still be somewhat functional to 125 - 150,000 miles, but as you have observed, gas mpg's and emissions will get worse.

Are the gas stations required to sell winter blend gasoline where you drive ? Cold weather and winter driving conditions can reduce your fuel economy significantly. Fuel economy tests show that, in short-trip city driving, gas mileage is about 12% lower at 20F than it would be at 77F. It can drop as much as 22% for very short trips (3 to 4 miles).

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post #4 of 11 Old 12-01-2019, 12:17 PM Thread Starter
TwoThousandWJ
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Originally Posted by CJ7-Tim View Post
1996 and newer OBDII-equipped vehicles, the recommended replacement interval for O2 sensors is 100,000 miles. They may still be somewhat functional to 125 - 150,000 miles, but as you have observed, gas mpg's and emissions will get worse.

Are the gas stations required to sell winter blend gasoline where you drive ? Cold weather and winter driving conditions can reduce your fuel economy significantly. Fuel economy tests show that, in short-trip city driving, gas mileage is about 12% lower at 20F than it would be at 77F. It can drop as much as 22% for very short trips (3 to 4 miles).
I can get two new O2 sensors for about $40 on amazon.com. Probably worth replacing them. Even if gas stations were not required to sell the winter blend, it would likely be a low-volume product and therefore much more expensive than the winter blend which would offset any additional efficiency gained by the summer product. As you probably know, in 2007, congress passed the Energy Independence and Security Act of 2007 in order to subsidize / benefit the corn producers despite the fact that it is horribly inefficient to harvest, refine, and burn ethanol as fuel. It's actually a net energy-negative process -- more energy goes into producing the ethanol from corn than is derived from the final product itself. And of course, since that time there is an oil glut with the US now being the largest producer of oil in the world:

https://en.wikipedia.org/wiki/List_o...oil_production

So it's now completely pointless to have E10, E15, E85 fuel etc, but we're stuck with it due to politics. Anyhow, since the WJ was not designed to run on fuel with higher concentrations of ethanol, I suspect the fuel economy penalty for it is higher than more modern vehicles. Curious if anyone has noted any benefit from Superchips ECU tuning to compensate.
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post #5 of 11 Old 12-01-2019, 12:46 PM
2oldjeeps
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Quote:
.Just Installed SuperChips, K&N Intake, iridian plugs

id go back...

99wj,143,000 miles
00xj,177,000 miles
10hummer3,74,000 miles
98xj,130,000 miles
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post #6 of 11 Old 12-02-2019, 01:56 AM
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What brand are those? You may go out of the proverbial frying pan and into the fire if you get subpar sensors. I've seen many instances over the years of people's economy getting worse until they replace the replacements with genuine Mopar parts.

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Originally Posted by TwoThousandWJ View Post
I can get two new O2 sensors for about $40 on amazon.com. Probably worth replacing them. Even if gas stations were not required to sell the winter blend, it would likely be a low-volume product and therefore much more expensive than the winter blend which would offset any additional efficiency gained by the summer product. As you probably know, in 2007, congress passed the Energy Independence and Security Act of 2007 in order to subsidize / benefit the corn producers despite the fact that it is horribly inefficient to harvest, refine, and burn ethanol as fuel. It's actually a net energy-negative process -- more energy goes into producing the ethanol from corn than is derived from the final product itself. And of course, since that time there is an oil glut with the US now being the largest producer of oil in the world:

https://en.wikipedia.org/wiki/List_o...oil_production

So it's now completely pointless to have E10, E15, E85 fuel etc, but we're stuck with it due to politics. Anyhow, since the WJ was not designed to run on fuel with higher concentrations of ethanol, I suspect the fuel economy penalty for it is higher than more modern vehicles. Curious if anyone has noted any benefit from Superchips ECU tuning to compensate.

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post #7 of 11 Old 12-02-2019, 02:17 AM
Ralph77
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I agree with CJ7-Tim and Kolak.
I replaced mine on my '00 XJ at about 150K just because.
No CEL's or anything. Just figured they needed to go.
Bite the bullet and spend the money when it comes to O2 sensors.
I am going to guess that an '00 WJ would come with NTK's like my '00 XJ did.
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post #8 of 11 Old 12-02-2019, 03:18 PM Thread Starter
TwoThousandWJ
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Originally Posted by Kolak View Post
What brand are those? You may go out of the proverbial frying pan and into the fire if you get subpar sensors. I've seen many instances over the years of people's economy getting worse until they replace the replacements with genuine Mopar parts.
You're probably right. For something like an oxygen sensor, probably makes sense to use a genuine Mopar part.
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post #9 of 11 Old 12-03-2019, 02:18 AM
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Let me know if I can assist. I carry genuine Mopar parts at a nice discount. You can PM me here on the forum or email me at [email protected] and we'll chat.

Quote:
Originally Posted by TwoThousandWJ View Post
You're probably right. For something like an oxygen sensor, probably makes sense to use a genuine Mopar part.

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post #10 of 11 Old 12-03-2019, 10:15 AM
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Mean while I'm over here getting around 12.5 city. Maybe I should give my pig a tune up.
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post #11 of 11 Old 12-08-2019, 09:56 PM
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For what its worth, Im getting an honest 16-17 mpg in and around town (2001 Limited 4.7 with 142K miles) and 21 mpg at speeds of 70 to maybe 72 mph. Over 75 mph the mileage drops off pretty fast. I use synthetic and the plugs and air cleaner are new. Im satisfied with those numbers and dont think they are exceptional.
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