Just did both air-fuel sensors and both O2 sensors on my 2008 today. I didn't find much in write-ups for this work so I figured it was either super easy and nobody needed it or not many have done it. Either way, here is what I did and a problem I ran into. Nothing earth shattering but maybe it will help someone considering doing on their own.
Symptoms leading up to the replacement: I was having some off idle hesitation up to about 2500 RPM or about 35MPH but it wasn't 100% of the time and nothing I tried could make it happen or make it stop. I posted a thread in the engine performance section about the issues I was having and got a lot of good advice. I cleaned the throttle body and bought a blue tooth OBD2 reader to get a better look at what was going on. I didn't have any codes but something wasn't right. After cleaning the throttle body (off engine) and taking a test drive with the OBD2 reader reporting on the Air/Fuel ratio commanded and the Air/Fuel ratio monitored nothing jumped out at me right away but I did notice that sometimes there was a pretty big Delta between the two and they were not really closely matched all the time. I was still running the OEM sensors and in the other thread had learned I was well past what was an expected life for all of them. I decided to go ahead and swap them all out in effort to restore the lost performance.
Specailty tools I used:
OBD2 Bluetooth
Torque Pro App
Lisle Dual Drive O2 offset wrench
Lisle O2 thread chase
I used Denso A/F ($108) and Denso O2 ($48) sensors from Rock Auto
Normal tools I used:
I didn’t keep a comprehensive list, I replaced all 4 sensors from underneath and I did use several 1/2" extensions with the Lisle wrench on the A/F sensors, 3' extension with U joint on the passenger side exhaust bracket upper 14mm bolts (from engine compartment), 14mm ratcheting box end on the driver’s side exhaust bracket upper bolts, 22mm box end wrench for the O2 sensors and 3/4" ratcheting box end wrench on the Lisle thread chase. The wiring harness plugs are set free by way of a standard screw driver with a narrow head and about a 3-4" length.
Drivers side A/F sensor:
The FSM alludes to removing a bracket with 3 bolts and by the picture in the FSM I wasn't sure what it was. Once under the driver’s side I saw what was in the way - a big bracket with two bolts on the engine block side and a single bolt on an exhaust coupling. Removing these bolts took a lot of effort and a cheater bar, which had either a bunch of torque from factory or had just taken a hard set over the years/miles.
Once the bracket was out of the way I was able to use a short/narrow standard screw driver to release the wiring harness from the sensor pig tail. I used the O2 wrench with 1/2" drive extension as a handle and a short cheater bar to get the A/F sensor to break free. Once the sensor was broken free it unscrewed by hand pretty easy. I ran the chase in/out the threads with little to no resistance. I coated the new Denso A/F sensor threads with their provided copper colored anti-seize and ran the sensor into the threads by hand until lightly seated. Once it was seated I used the Lisle O2 wrench to seat the sensor with a reasonable amount of torque.
Passenger side A/F sensor : The exhaust bracket was a PITA to remove. I could only reach the two upper bolts with a 3' extension and a U joint. Even then it took a cheater bar to pop each one free. The bottom bolt came out without issue. Getting the wiring harness free took the narrow standard screw driver but by the time I had my arm up where it needed to be I couldn’t see the plug so I had to do it by feel. Took me a couple tries to unplug the sensor. Removing the A/F took the Lisle O2 wrench but this time with a 3/8 socket wrench in the top side of the O2 wrench and a cheater bar on the socket wrench handle. Once it popped free, it was easy to un screw by hand. I ran the O2 thread chase in/out with little to no resistance, applied the copper color anti seize and installed the A/F sensor.
Drivers side O2 sensor : The sensor unplugs same as the A/F sensor with the short narrow standard screw driver. I used a 22mm 12 point box end to unscrew the sensor (the pig tail on the sensor fits through the box). The O2 sensor was tough to break free and just as tough to unscrew to remove. A couple times I stopped to make sure I wasn’t accidentally tightening it by accident. I even pondered if it might be reverse threaded for some reason. In the end it came out with a lot of effort. The threads on the old sensor looked like crap and I was worried it might have galled the threads and I was right. The threads in the exhaust pipe were in bad shape. It took a couple starts to get the O2 thread chase started square but once started I would turn it in about 1/4 turn and then back it off 1/2 turn or more and run it back in another 1/4. I pulled it out to clean and relube several times. It took a while but I eventually got the threads re-cut and cleaned up. I was able to install the new sensor with the copper anti seize without drama.
Passenger side O2 sensor: After all the drama on the driver’s side I was a little hesitant to pull this sensor out. I was able to unplug the pig tail and pop the sensor free without drama. This one unscrewed by hand once popped free and the thread chase ran in/out with little resistance. I coated the threads of the new sensor with the copper anti-seize and installed it by hand and set the final torque with the 22mm box end wrench before plugging the pig tail back in.
I re connected the negative side of the battery and started the FJ. It fired right up to a pretty fast idle, like it would on a very cold day (it was about 75F today). The initial idle seemed to have a little roughness to it but there were no apparent exhaust leaks or dash warning lights. I shut off the engine, plugged in the OBD2 scanner and started the engine. I ran through the scanner readings and everything seemed to be ok with no codes. I took a couple runs around the block and everything ran great. I took a longer test drive after cleaning up and its very noticeably better. Throttle response is back to what I remember and everything is smooth at idle. The initial idle roughness I felt at first start went away fast and everything settled in during this longer test drive.
I am really happy I bought the O2 thread chase! Both Lisle tools were great quality (forged) and I am pleased with both the pruchases. I almost skipped the chase but I would have been SOL today without it. I have no idea what happened with the threads in the drivers side O2 sensor, maybe I somehow messed it up while unscrewing it or maybe it got jacked up when it was installed on the assembly line. I'll probably never know but I am damn happy I had that thread chase and was able to recover from that situation.
Symptoms leading up to the replacement: I was having some off idle hesitation up to about 2500 RPM or about 35MPH but it wasn't 100% of the time and nothing I tried could make it happen or make it stop. I posted a thread in the engine performance section about the issues I was having and got a lot of good advice. I cleaned the throttle body and bought a blue tooth OBD2 reader to get a better look at what was going on. I didn't have any codes but something wasn't right. After cleaning the throttle body (off engine) and taking a test drive with the OBD2 reader reporting on the Air/Fuel ratio commanded and the Air/Fuel ratio monitored nothing jumped out at me right away but I did notice that sometimes there was a pretty big Delta between the two and they were not really closely matched all the time. I was still running the OEM sensors and in the other thread had learned I was well past what was an expected life for all of them. I decided to go ahead and swap them all out in effort to restore the lost performance.
Specailty tools I used:
OBD2 Bluetooth
Torque Pro App
Lisle Dual Drive O2 offset wrench
Lisle O2 thread chase
I used Denso A/F ($108) and Denso O2 ($48) sensors from Rock Auto
Normal tools I used:
I didn’t keep a comprehensive list, I replaced all 4 sensors from underneath and I did use several 1/2" extensions with the Lisle wrench on the A/F sensors, 3' extension with U joint on the passenger side exhaust bracket upper 14mm bolts (from engine compartment), 14mm ratcheting box end on the driver’s side exhaust bracket upper bolts, 22mm box end wrench for the O2 sensors and 3/4" ratcheting box end wrench on the Lisle thread chase. The wiring harness plugs are set free by way of a standard screw driver with a narrow head and about a 3-4" length.
Drivers side A/F sensor:
The FSM alludes to removing a bracket with 3 bolts and by the picture in the FSM I wasn't sure what it was. Once under the driver’s side I saw what was in the way - a big bracket with two bolts on the engine block side and a single bolt on an exhaust coupling. Removing these bolts took a lot of effort and a cheater bar, which had either a bunch of torque from factory or had just taken a hard set over the years/miles.
Once the bracket was out of the way I was able to use a short/narrow standard screw driver to release the wiring harness from the sensor pig tail. I used the O2 wrench with 1/2" drive extension as a handle and a short cheater bar to get the A/F sensor to break free. Once the sensor was broken free it unscrewed by hand pretty easy. I ran the chase in/out the threads with little to no resistance. I coated the new Denso A/F sensor threads with their provided copper colored anti-seize and ran the sensor into the threads by hand until lightly seated. Once it was seated I used the Lisle O2 wrench to seat the sensor with a reasonable amount of torque.
Passenger side A/F sensor : The exhaust bracket was a PITA to remove. I could only reach the two upper bolts with a 3' extension and a U joint. Even then it took a cheater bar to pop each one free. The bottom bolt came out without issue. Getting the wiring harness free took the narrow standard screw driver but by the time I had my arm up where it needed to be I couldn’t see the plug so I had to do it by feel. Took me a couple tries to unplug the sensor. Removing the A/F took the Lisle O2 wrench but this time with a 3/8 socket wrench in the top side of the O2 wrench and a cheater bar on the socket wrench handle. Once it popped free, it was easy to un screw by hand. I ran the O2 thread chase in/out with little to no resistance, applied the copper color anti seize and installed the A/F sensor.
Drivers side O2 sensor : The sensor unplugs same as the A/F sensor with the short narrow standard screw driver. I used a 22mm 12 point box end to unscrew the sensor (the pig tail on the sensor fits through the box). The O2 sensor was tough to break free and just as tough to unscrew to remove. A couple times I stopped to make sure I wasn’t accidentally tightening it by accident. I even pondered if it might be reverse threaded for some reason. In the end it came out with a lot of effort. The threads on the old sensor looked like crap and I was worried it might have galled the threads and I was right. The threads in the exhaust pipe were in bad shape. It took a couple starts to get the O2 thread chase started square but once started I would turn it in about 1/4 turn and then back it off 1/2 turn or more and run it back in another 1/4. I pulled it out to clean and relube several times. It took a while but I eventually got the threads re-cut and cleaned up. I was able to install the new sensor with the copper anti seize without drama.
Passenger side O2 sensor: After all the drama on the driver’s side I was a little hesitant to pull this sensor out. I was able to unplug the pig tail and pop the sensor free without drama. This one unscrewed by hand once popped free and the thread chase ran in/out with little resistance. I coated the threads of the new sensor with the copper anti-seize and installed it by hand and set the final torque with the 22mm box end wrench before plugging the pig tail back in.
I re connected the negative side of the battery and started the FJ. It fired right up to a pretty fast idle, like it would on a very cold day (it was about 75F today). The initial idle seemed to have a little roughness to it but there were no apparent exhaust leaks or dash warning lights. I shut off the engine, plugged in the OBD2 scanner and started the engine. I ran through the scanner readings and everything seemed to be ok with no codes. I took a couple runs around the block and everything ran great. I took a longer test drive after cleaning up and its very noticeably better. Throttle response is back to what I remember and everything is smooth at idle. The initial idle roughness I felt at first start went away fast and everything settled in during this longer test drive.
I am really happy I bought the O2 thread chase! Both Lisle tools were great quality (forged) and I am pleased with both the pruchases. I almost skipped the chase but I would have been SOL today without it. I have no idea what happened with the threads in the drivers side O2 sensor, maybe I somehow messed it up while unscrewing it or maybe it got jacked up when it was installed on the assembly line. I'll probably never know but I am damn happy I had that thread chase and was able to recover from that situation.