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Replacing O2 Sensors PDF Print E-mail
Written by Sherry Nichols   
Sunday, 29 June 2008

Click to enlargeMy jeep hasnít been running properly for quite some time. Originally, it sputtered and backfired, lost power as though running out of gas and then died on the side of the highway on my way home from a run last spring.  This problem continued to be intermittent and frustrating over the past year.

I changed clothes and went outside, full of optimism, to examine the situation. I became disheartened when I realized that I didnít have any idea what I was supposed to do next. I had a socket in hand that I knew had to go on the old O2 sensor so I set about finding a tool that would turn the socket. Locating a torque wrench that looked like it would work I went under the jeep to see what I could accomplish.

Mark came out, probably figuring that because I hadnít returned to the house I was surely getting myself in trouble. He got the appropriate tools for me (a torque wrench not being among them) and gave me ample support and directions from the workshop doorway where he sat holding his head.

I was working on the O2 sensor before the catalytic converter, relatively easy to get to but impossible to turn. Mark brought out the PB Blaster and fluid film to help loosen it, advising me to not spray too much on Ė shortly after I had done just that - getting it all over myself.

While waiting for that to work we moved to the back to see about the O2 sensor after the catalytic converter. This is conveniently located on top of the catalytic converter behind the muffler and next to the transfer case all of which is protected by the skid plate, leaving approximately 1 inch of space for the socket wrench to turn Ė barely enough to allow it to ratchet. I sprayed the PB Blaster on that one, using even more this time due to the inability to articulate that little straw-like thing to get to the bolt.

Back to the front where I tried with all my newly found canoeing muscles to get the sensor to budge. I was determined to go on the run that night. Finally, after several exhausting attempts, I heard that wonderful sound of a part giving way! The O2 sensor is shaped like a spark plug and screws in to the exhaust pipe, once loosened it is easy to replace. Mark had unhooked the wiring; I took the old sensor out and put the new one in Ė just like that. He said I didnít need to worry about tightening it too much (whether this is because I am not strong enough or that it canít be over tightened remains unknown) so I pulled until I couldnít budge it.

Click to enlargeThe rear sensor is much more difficult. I unhooked the electrical thingy and spent the next 20 minutes or so trying every possible angle and configuration of extensions to allow leverage. Out comes the impact wrench Ė if I could just figure a way to get that to hook on to the socket I was sure that would work. Otherwise, there was no way that I was going to get that sensor out.

The impact wrench is heavy, the space to maneuver it, along with the articulated ratchet adaptor things to attach to the sensor socket (you will need one of these when replacing either sensor and I will gladly lend you the one we have) is tight. Make sure you determine which way your impact wrench is set before attaching it to your assorted tools or you will regret it. After putting it back up there, having taken it down to see if it was set to tighten or loosen, I had to hook up the air hose to the end. This is also not easy as it requires two hands yet you only have one available as the other is holding the impact wrench to the ratchet assembly. Carefully balancing the impact wrench on the transfer case I attached the air and pressed the trigger. The socket wasnít moving.

Mark said it may take a while so I pressed the trigger longer. At this point you will also need to be careful where you hold the impact wrench as it moves a lot and can bang your fingers into either the muffler or the transfer case causing you to curse. Becoming frustrated at everything but the socket moving I stopped and decided that the articulated thing connecting the impact wrench to the socket must be the issue. The spring that fell in my face when disconnecting the two confirmed this theory.

How about if I just try to get the impact wrench to connect directly to the socket? Moving it around the transfer case (did I mention that it is heavy?) I tried to line it up with the socket but it wasnít cooperating. Finally, I found the right angle and heard that satisfying sound of a wrench connecting to a socket. Throughout this ordeal Mark was explaining options to me, handing me parts and assuring me that I would figure it out.

Once directly connected, the impact wrench made short work of loosening the socket. I was so relieved that it actually worked. I took the old sensor out and put the new one in, believing that the hard part was behind me. Getting the new sensor in requires tightening it by hand, to avoid cross threading it, before using the socket and wrench. The skid plate and muffler force you to use your left hand to do this. I have to admit that, after all of the other hard things to do, this was the hardest part. These things do not thread themselves easily and it is hard to tell when they are threaded properly as, at least in my case, I was only able to turn it a few times before it became tight enough that I couldnít move it. It goes from falling out, after fooling you that it is threaded in there, to too tight very quickly.

Knowing that I was running out of strength in my left hand and that I had to finish or fail I decided that I had done it right and used the socket and wrench to tighten it, one little ratchet at a time (the space thing) until it would move no further. I hooked up the wiring and was anxious to see if the jeep would start. I washed my hands with some sort of green spray, used a dirty rag to wipe them dry and turned the key Ė delighted and proud to hear the sound of a running jeep.

I took it out for a test drive and found that it ran better, shifted more smoothly and had more power. Is it all my imagination? Perhaps. Did this resolve the problem? I certainly hope so. Weíll see how it runs tonight.

Thank you to my wonderful husband who got out of bed to help me, you are an ace mechanic even when you canít see whatís going on.


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