Justin@VMP
July 4th, 2008, 08:32 AM
It's important for any vehicle to have properly functioning narrowband O2 sensors, the front ones do all the work and are the most important. The rear ones can be deleted or turned off if you don't have to pass an emissions test, as they are only there to monitor cat efficiency.
The factory Ford and Motorcraft brand O2 sensors seem to work the best, I would not recommend the cheaper aftermarket replacements like Bosch. I've seen them fail to heat up in a reasonable amount of time.
Here is an example of an 03/04 cobra with stock headers, where the owner replaced the O2 sensor on one bank with a bosch replacement, because he thought his stock sensor was bad.
http://www.vmptuning.com/pics/coldbosch.jpg
The yellow line is time running, the dark purple line is the voltage signal from the bosch O2, and the dark red/brown line is the stock O2. You can see the factory O2 begins to start switching and shows a strong high to low swing (from about .2v to .8v with a consisent wave shape) within 15 seconds, whereas the bosch O2 takes longer and switches very weakly. In the case of longtubes the bosch O2s may never get hot enough to light off, I've heard of this happening before. I've seen bosch O2s thats take a minute to warm up and the stock O2 next to it takes less than half that time. The bosch sensors seem to have very weak internal heater circuits
Most people use Bosch sensors because of cost and availability, most Ford dealers want over $100 for an OEM or motorcraft brand O2 sensor. There are less expensive way to get some brand name parts though, you can buy from a motorcraft dealer and usually spend $60-$80 for an O2, or even better yet buy from one of the online discount auto parts stores/motorcraft dealers like www.rockauto.com
O2 sensors should usually be replaced every 50-100k miles, and more often if you use leaded fuel on a regular basis. It's important that they switch consistently (not slow and lazily) so the computer can properly adjust short term fuel trims and learn part throttle air fuel corrections. Even if the car is tuned perfectly, you still want adaptive learning to take up that last 3-5% for things like fuel variances.
Blowing a HG or getting antifreeze on them tends to mess them up. You should use O2s meant for your specific year, as there have been some changes over the years. 99+ O2s are designed to have the heater circuit PWM by the PCM, while 98 and older use a more basic control method I am told.
The factory Ford and Motorcraft brand O2 sensors seem to work the best, I would not recommend the cheaper aftermarket replacements like Bosch. I've seen them fail to heat up in a reasonable amount of time.
Here is an example of an 03/04 cobra with stock headers, where the owner replaced the O2 sensor on one bank with a bosch replacement, because he thought his stock sensor was bad.
http://www.vmptuning.com/pics/coldbosch.jpg
The yellow line is time running, the dark purple line is the voltage signal from the bosch O2, and the dark red/brown line is the stock O2. You can see the factory O2 begins to start switching and shows a strong high to low swing (from about .2v to .8v with a consisent wave shape) within 15 seconds, whereas the bosch O2 takes longer and switches very weakly. In the case of longtubes the bosch O2s may never get hot enough to light off, I've heard of this happening before. I've seen bosch O2s thats take a minute to warm up and the stock O2 next to it takes less than half that time. The bosch sensors seem to have very weak internal heater circuits
Most people use Bosch sensors because of cost and availability, most Ford dealers want over $100 for an OEM or motorcraft brand O2 sensor. There are less expensive way to get some brand name parts though, you can buy from a motorcraft dealer and usually spend $60-$80 for an O2, or even better yet buy from one of the online discount auto parts stores/motorcraft dealers like www.rockauto.com
O2 sensors should usually be replaced every 50-100k miles, and more often if you use leaded fuel on a regular basis. It's important that they switch consistently (not slow and lazily) so the computer can properly adjust short term fuel trims and learn part throttle air fuel corrections. Even if the car is tuned perfectly, you still want adaptive learning to take up that last 3-5% for things like fuel variances.
Blowing a HG or getting antifreeze on them tends to mess them up. You should use O2s meant for your specific year, as there have been some changes over the years. 99+ O2s are designed to have the heater circuit PWM by the PCM, while 98 and older use a more basic control method I am told.