O2 sensor replaced—wow

StG58

StG58

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Just replaced the upstream O2 sensor on my 99 SE. The one that was in there was factory original.

The little Jeep wasn't throwing codes or displaying any overt symptoms of an O2 sensor malfunction. The only indications that an O2 sensor wasn't functioning at peak efficiency was a very gradual increase in fuel consumption and a barely perceptible loss of power. Hey, it's a 2.5. A slight, gradual loss of power isn't all that noticeable, right?

The difference pre and post replacement IS seat of the pants noticeable though.

O2 sensors are consumable parts, like spark plugs.
 
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Awesome! It makes a big difference. I have 4 on my 2001 and I replaced all 4 when I was doing the manifold back exhaust system a while back. It made a whole new driving experience. Glad to hear it wakes up the 2.5 as well. If you’re still running the stock cat and exhaust I bet there’s more to be had there too.
 
I had a stumble/bad hesitation on cold acceleration. Sometimes erratic idle. Check engine light came on for a 02 heater circuit malfunction. Installed a new NTK sensor, old sensor looked like it had been installed with pliers. New sensor cured stumble, idle problem and it seems to have maybe increased MPG and acceleration. Definitely runs better.
 
They are on the rockauto closeout site, any brand work or is there a preference? Might as well do mine, the previous 5 owners probably neglected those too.
 
Gollywomper said:
I have heard to only use NGK/NTK 02 sensors. Other brands have caused some issues. I have no first hand experience in what those issues were.
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RA has API, never heard of them, they are $17 and $18.

Disregard, found the O2 thread, NGK ones are only a few $$ more.
 
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Good to hear, I may try and change mine before heading to tahoe next month. I know I get between 12-14 mpg now. If I see anything in the 14's I'm usually pretty happy. Would be really cool to see if I could get anything above 15 as I never have since I've owned it.
 
Get a sensor socket when you order up the NGK/NTK sensors. Makes a world of difference on install and removal. Also, no silicone waterproofing gunk on the electrical connector. The sensor needs to vent the internal cavity, and the new ones vent through the wiring. Who knew? Your trivia tip of the day.
 
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Use a 22mm or 7/8" socket to remove the old O2 sensors, don't try to use a slotted O2 socket to remove it as the slot weakens them so they're apt to slip on the O2 sensor. That is because old O2 sensors are usually seized/tight and the slotted type of O2 sensor socket will often open up and slip around the O2 sensor when using the power needed to extract it. Cut the wiring off the old O2 sensor before slipping the wrench over it.

A slotted socket is fine for installing a new O2 sensor. Its wiring is passes through the socket's slot while tightening it.
 
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StG58 said:
Just replaced the upstream O2 sensor on my 99 SE. The one that was in there was factory original.

The little Jeep wasn't throwing codes or displaying any overt symptoms of an O2 sensor malfunction. The only indications that an O2 sensor wasn't functioning at peak efficiency was a very gradual increase in fuel consumption and a barely perceptible loss of power. Hey, it's a 2.5. A slight, gradual loss of power isn't all that noticeable, right?

The difference pre and post replacement IS seat of the pants noticeable though.

O2 sensors are consumable parts, like spark plugs.
Click to expand...

Dude, tell me about it! I bought this 99 last year (first TJ) and thought that I had a little exhaust leak somewhere. It had a bit of a tinny knock on acceleration, would hesitate ever so often but never had a check engine light. I replaced the O2 sensors one day just because I noticed some chaffing on the upstream wires due to them not being secured, and ALL of the small driveability issues went away to include the noise I attributed to an exhaust leak. The thing runs like a top now, I couldn't believe it.

I've been a car guy for a long time (mostly Japanese & German, used to fix those for a living) and always had the perception of O2 sensors as much more digital than what I've learned that they are on these TJs. With most of the stuff I grew up on the O2 sensors typically didn't cause issues without asserting a check engine light and weren't ever considered maintenance items like they are here. Love learning new stuff!
 
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I replaced mine a few months back after throwing a code. I sprayed them with Kroil a week before and then again the night before I did the job. They both came out easily.
 
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I always tell people, replace your O2 sensors every 80k or so. Also, DO NOT just replace one because it’s bad, replace ALL OF THEM at the same time.

People need to understand that regardless of whether they are bad or not, they are general maintenance items.
 
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The downstream O2 sensor mounted on the catalytic converter on older TJs rarely goes bad and its only job is to monitor the cat for proper operation. It doesn't affect how the engine runs. I'd only replace the upstream O2 sensor on those older models without the pair of precats. :)
 
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80-100,000 miles is a good change interval. The ceramic in the sensor gets clogged with combustion byproduct and starts to "lag" changes in combustion efficiency (14.7 to 1 air / fuel ratio) over time. Our TJ sensors / ECM sample at around 60 (don't quote me on the exact number) times a second. A small lag in the voltage change fools the ECM. Not enough to throw a code and go open loop, but bad enough to effect performance.
 
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Jerry Bransford said:
Use a 22mm or 7/8" socket to remove the old O2 sensors, don't try to use a slotted O2 socket to remove it as the slot weakens them so they're apt to slip on the O2 sensor. That is because old O2 sensors are usually seized/tight and the slotted type of O2 sensor socket will often open up and slip around the O2 sensor when using the power needed to extract it. Cut the wiring off the old O2 sensor before slipping the wrench over it.

A slotted socket is fine for installing a new O2 sensor. Its wiring is passes through the socket's slot while tightening it.
Click to expand...

If you do have or need a slotted socket, put a worm drive clamp around the socket and tighten it. Kept mine from expanding and slipping.
 
Jerry Bransford said:
The downstream O2 sensor mounted on the catalytic converter on older TJs rarely goes bad and its only job is to monitor the cat for proper operation. It doesn't affect how the engine runs. I'd only replace the upstream O2 sensor on those older models without the pair of precats. :)
Click to expand...

So by older TJ's you are talking like my 99 right?

On a side not, sure glad the TJ's 02 sensors aren't as expensive as the Mazda Miata. I just spent 174 bucks on a downstream sensor for it. The cheap one was 99 dollars. My very respected parts guy told me not to go with the cheap one as it was universal and didn't have a good reputation.

That being said, I will probably add this to my list of things to eventually replace. I can't say how old mine is and the Jeep has 196k miles, so probably wouldn't hurt. :D
 
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