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Old 07-25-2010, 08:47 PM   #1
FC
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Replacing O2 Sensor on JGC

Not a lot of awesome content, but dammit not nearly enough of us get dirty with the car, so I figured I'd post re: my bit of weekend car wrenching.

What a PITA.

I felt pretty lucky because it was the easiest to get to out of the 4. However, when it became apparent that the threads were virtually fused, it was probably the worst sensor to get enough leverage on to break the threads loose.

In the end, the special O2 tool was useless since it was vary tall, and way too loose. I took a Dremel with the fiberglass-reinforced cutter and cut everything above the hex (22mm). I then was able to fit a standard 6-point socket but I still could not get enough leverage with a standerd 1/2" ratchet. I went out and bought this.

Not only did it let me get the handle out from the innards of the Jeep but it was longer too. I stuck a tube for added leverage and finally broke it loose. Brutal experience considering the heat and a very bad wrist (weird soccer incident).

Handy JGC (WJ) website. Note the O2 sens I replaced was 2/2 (right back, downstream) on the 4.7L.

Anyhow, it could be just me but this is what I noticed after a brief drive (enough to just get the engine to temperature):

1. The car felt noticeably faster. I've been driving it daily since they tore up the road to my work and it was a pretty immediate sensation of improved response and power.

2. The jeep has been averaging a dysmal 12.X mpg recently without aggressive driving. Even with a decent amount of hwy mixed in I don't crack 15mpg. This compares poorly with the 14.7mpg around town with pretty aggressive driving when I got it, and 17+mpg with hwy driving thrown in. I reset the mpg meter and in the 2-3 mile drive with hills, stops and goes and a bit of punching, the car read 15.8mpg when I got back home.

3. This is the weird one. I am 99.9% certain I installed everything correctly (not much to it), yet the exhaust sounds different. There is a bit of muscle car-like burble with brief taps of the gas at crawl speeds (I noticed when trying to get the jeep back on the rhino ramps). If I rev it, the engine sounds smooth and the exhaust normal, but the tone has definitely changed a bit. This is not something I remembered from a year ago. A simple hover near the sensor doesn't reveal the tale tale sound of an exhaust leak to my ear (engine idling).

Now, to be fair, the CEL did come up within a few months of ownership but then went away. Then again recently and it went away again. Several weeks ago it came on for good.

Could it be that even though the sensor was well enough to make the OBD shut the light off it still wasn't working 100%? In other words, does a O2 sensor's performance deteriorate until it is so bad that the light comes on, or is it more of a yes/no fault where if it is not perfect the light gets triggered?

Last edited by FC; 07-26-2010 at 03:21 PM.
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Old 07-26-2010, 12:45 AM   #2
Terri Kennedy
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Quote:
Originally Posted by FC View Post
In the end, the special O2 tool was useless since it was vary tall, and way too loose. O took a dremel with the fiberglass reinforced cutter and cut everything above the hex (22mm). I then was able to fit a standard 6-point socket but I still could not get enough leverage with a standerd 1/2" ratchet. I went out and bought this.
The Sears link is a session that timed out.

Yup, exhaust stuff is generally the worst part to work on. The nature of the system means that the fittings are generally corroded and frozen.

The worst experience I had with an exhaust involved a pair of crowfoot wrenches in wobble sockets. I bet you can guess which car...

Quote:
Now, to be fair, the CEL did come up within a few months of ownership but then went away. Then again recently and it went away again. Several weeks ago it came on for good.
Got a code reader? If not, have your Autozone read it for free.

Quote:
Could it be that even though the sensor was well enough to make the OBD shut the light off it still wasn't working 100%? In other words, does a O2 sensor performacnce detriorate until it is so bad that the light goes on, or is it more of a yes/no fault where if it is not perfect the light gets triggered?
Depending on what goes wrong with the sensor, it can lead to a gradual deterioration of its ability to report accurate information to the engine management computer. The computer is supposed to set the CEL if it determines that the car is operating outside the allowable emission standards.

The computer also adapts over time, but within what it thinks are acceptable limits. This compensates for normal wear, individual manufacturing variations of the various components, and so on.
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Old 07-26-2010, 08:18 AM   #3
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The Sears link is a session that timed out.
Sorry, it was a Craftsman 1/2 in. Drive Flex Head Quick Release Teardrop Ratchet.



Quote:
Originally Posted by Terry Kennedy
Yup, exhaust stuff is generally the worst part to work on. The nature of the system means that the fittings are generally corroded and frozen.

The worst experience I had with an exhaust involved a pair of crowfoot wrenches in wobble sockets. I bet you can guess which car...


Got a code reader? If not, have your Autozone read it for free.


Depending on what goes wrong with the sensor, it can lead to a gradual deterioration of its ability to report accurate information to the engine management computer. The computer is supposed to set the CEL if it determines that the car is operating outside the allowable emission standards.

The computer also adapts over time, but within what it thinks are acceptable limits. This compensates for normal wear, individual manufacturing variations of the various components, and so on.
My buddy has one. But I later found through here (and the manual, had I read it) that the car will spit out the codes if you play with the key.

The codes are P0161 and P0158, both of which relate to the sensor I replaced.

But if you look at the section on clearing the codes, it reads:

After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again.

DTCs can be erased anytime with a DRB III. Erasing the DTC with the DRB III erases all OBD II information. The DRB III automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.


I can unplug the battery and it will clear the codes. This is what I did as my inspection sticker was due, but I got bagged and was told I had to drive 150 miles and come back. Of course the light eventually came back on. I didn't care because I wanted to fix this anyway. I just wanted more time. But the rejection sticker only gives me 30 days before I have to pay the fee again.

If I clear the codes via a reader or battery, I will need to drive another 150 miles. It seems from that paragraph that three good trips will clear the fault as well. Maybe I'm reading it wrong.
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Old 07-26-2010, 03:00 PM   #4
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One thing that a lot of the Jeep guys do before they wrench on their exhaust is hit any threaded connections affected with PB Blaster or Liquid Wrench the night before. I've done this a few times and it's surprising how well the products work.

Also, would it have been easier to remove the section of exhaust the O2 sensor was on so you would have had easier access to the sensor with the header pipes off of the rig?

Of course, you're done with it now so it doesn't really matter that much.
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Old 07-26-2010, 03:26 PM   #5
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I did use liquid wrench but only gave it a couple of hours to penetrate. The can says to wait a few minutes. I guess I should have done it overnight.

Removing the secion of exhaust would have been an annoying and long job. If the new ratchet+liquid wrench did not cut it, I would have moved on to torching the pipe and freezing the socket (something that has worked for me before). I just did not have the jeep high enough off the ground to safely use the torch. The last step would have been what you suggest. I was starting to get concerned that it would require more torque to get the sensor out than the exhaust could bare in situ. The sensor was located in the middle of a pretty long span between supports.

Last edited by FC; 07-26-2010 at 03:58 PM.
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Old 07-26-2010, 03:35 PM   #6
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Speaking of Jeep exhaust.....my catalytic converter has started rattling like crazy once it gets hot.

I guess the money I saved by using junk yard parts to fix the A/C are now going towards a replacement cat.
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Old 07-27-2010, 01:32 PM   #7
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Well, it took a few more than "three good trips," but the light is finally gone.
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Old 07-27-2010, 01:33 PM   #8
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Speaking of Jeep exhaust.....my catalytic converter has started rattling like crazy once it gets hot.

I guess the money I saved by using junk yard parts to fix the A/C are now going towards a replacement cat.

Can't you just get a couple of stainless steel straps and tighten the crap out of them, or is it internal?
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Old 07-27-2010, 02:03 PM   #9
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It's something internal. I suspect the packing material is breaking up. I'll probably ignore it for a few months before I bother really looking at it.

Hopefully it won't plug the exhaust system.
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Old 07-27-2010, 02:15 PM   #10
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Speaking of Jeep exhaust.....my catalytic converter has started rattling like crazy once it gets hot.

I guess the money I saved by using junk yard parts to fix the A/C are now going towards a replacement cat.
Sweet! Sounds like it's time for an upgrade to the exhaust system.
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