97 Contour O2 Sensor Questions

Car:     1997 Ford Contour, 100,000 + miles, no major problems.
History: About a week ago the car was in the transmission shop to replace a bad shift
sensor. At that time the mechanic said that one O2 sensor was bad and replace it as well. The car ran fine for a while.
The check engine light came on yesterday and displayed the generic code "P0304" on my ODB2 code reader (#4 cylinder misfire). I checked and replaced four bad plugs. It still runs rough and again displayed the same code, only now I also have Catalyst Monitor, Heated Catalyst Monitor, and Oxygen Sensor Heater Monitor displayed. There is also a burning smell.
How many O2 sensors are there? Could there be another problem as well?
I'm a little worried since catalytic converters can reach temps as high as 3000 degree F and can start fires.
Thanks, Mark
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I think the trans shop broke the first... and screwed up on the install of the generic replacement... but that's just a wild guess.
There are two for each cylinder bank.
Take it back, point out that they changed that O2 sensor on that bank and now it doesnt run right... betcha there's wiring splices between the new one and connectors.
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we get this fault code all the time with focus and mondeo its allways the coil pack change the coil pack, and road test you'll see the differance...
there'es allways one 02 sensor but some have 2 (before and after the cat, to check the function and operation of the cat) im from the UK so maybe yours if differant tho..
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ford_technical_ wrote:

Thanks. After I posted yesterday I thought about it some more. (Logically thinking) I realized that the sensor(s) probably returned a code because the ignition system is at fault. Thus the misfire code on cyl #4. Thanks for the suggestion.
Mark
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Backyard Mechanic wrote:

That's interesting. I didn't see any splices but I will look it over more closely. Thanks!
Mark
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