Sorry if this has been gone over before, but the search was very vague or riddled with stuff other than 02 answers.

1. Which of the sensors usually need replacement? Upstream, downstream, or all 4?

2.At what mileage do they most likely need to be replaced? I read 30k?

3. Who's found the best price for them (stock or Bosch) and where?

4. Are the Bosch that much better than stock replacements?

5. Any tips, tricks, or things to watch for when removing/replacing them?

6. Has anyone tried cleaning them with a MAF aerosol cleaner or similar product?

Thanks for any help you may have on this.

I'm not throwing a code or rough idle, just looking to maintain max MPG.

 

1. Personally, I like to replace all 4 but you can get away with just the two upstream.

2. Generally replace at around 30-50K.

3. I haven't priced them yet, but anybody outside of Ford will have a better price.

4. I'm not 100% sure but I believe the stockers are Bosch.

5. Soak them in a good penetrating oil and buy a proper socket made for removing O2 sensors. They can be stubborn sometimes and the socket will help prevent rounding off the corners. Be careful of the wiring harness so you don't damage a connector. Typically the new sensors will come with anti seize, if not make sure to buy some to make the next removal easier.

6. DO NOT use any type of cleaner on an O2 sensor! They're designed to be dry and spraying one will kill it. Besides, you've already gone through the trouble to remove them, just throw a new one in and be done with it.

 

30-50k replacement, depending on driving habits, fuel, etc...

Best to replace all 4.

It is actually best to understand the system; the rear O2s do actually work with the PCM for the adaptive fuel strategy. Now there gain or effect on the system isn't as darastic as the fronts. The front O2s has a gain in the tenths(larger), while the rear O2s have a gain in the thousands(minor). I could go on forever, but when you say you want "max mpg", replace all four.

 

So by changing all 4 sensors can you expect an increase in MPG?

 

What would be the ill effect of having the rear 02 turned off if you take out the cats?

 

No, you'll maintain/restore the MPG the engine had when it was new.

 

Dont waste your money on putting new o2 sensors in at 50k miles. The cost of these sensor I beleive is around $70 per sensor. If you know someone with a scope you can easily see how fast the sensors react voltage wise ( most older sensors have a slow reaction time hence need replacement or voltage pattern stays the same). An 02 sensor is a voltage generator which means it makes a voltage signal based on oxygen in the exhaust and sends a signal back to the pcm. The pcm then uses this signal and a few other signlas from various sensors to control pulse width to the fuel injectors (how long they stay on). An 02 usually reads between 500mv and 1v I believe. 500mv=lean 1v = rich. Best way to bench test is to remove the sensor and put it in a vise( not to tight). Then take a gas torch around the sensor and hook up you volt meter to the signal return wire. See how fast the voltage reacts from the change in oxygen surrounding the sensor. It it a waste of money to put on parts when the are not needed. Just my 2 cents. Plus the cost of 4 sensors will be more then you will save in fuel in the long run. Hope this was helpful.

 

Not that much. Because the gain is smaller it will 'fine tune', the rear O2s work off what is already stored in the KAM.

The best way to understand is that the front O2s switch at .45v (technically .449); The PCM forces a rich/lean condition to 'switch' the O2s, it modifies the fuel pulse width in order to do this. And lets not worry about the what the MAF is doing at this point.

**** my playstation froze, ill finish later....

 

Sounds like a good start. I've found upstreams to cost $63 ea. and downstreams to run $50 ea. OUCH!!!

Anyone find these cheaper?

 

thats cheaper than what i paid. my front passenger side sensor went out and i needed to do it right away. if i remember correctly, the auto part stores didnt have the oem style sensors in stock, so i had to get the universal type, which involves cutting and splicing wires.

the one i had to replace was hard to get too and a B*&CH to get out. i bought the special tool and roke it trying to get it out. i replaced the tool, heated up th sensor with a torch, smeared some candle wax on it to penetrate the threads and finally was able to get it out.

to be honest, i wouldnt reccommend replacing the fronts unless there was something wrong with them. too much of a PITA

 

This is honestly the first time I've heard of changing O2 sensors at 50k, or as preventative maintenance. I've pretty much always heard change them when they throw a code or a drastic change in fuel mileage or driveability.