Thread: Whats wrong with my Ford?

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denny your real close but no cigar. the o2 sensor is a battery that works with two dissimilar fluids that fluid is o2 the air outsie the o2 sensor is 21% o2 diference between the outside samole and the inside sample generates current that the computer reads in milivolts up to 1 tenth of a volt the more 02 on the inside sample the lower the voltage thats why if you have a missfire the 02 goes out the exaust unburned the computer sees low voltage and sets a lean mixture code .....ted

Originally Posted by ted dehaan

denny your real close but no cigar. the o2 sensor is a battery that works with two dissimilar fluids that fluid is o2 the air outsie the o2 sensor is 21% o2 diference between the outside samole and the inside sample generates current that the computer reads in milivolts up to 1 tenth of a volt the more 02 on the inside sample the lower the voltage thats why if you have a missfire the 02 goes out the exaust unburned the computer sees low voltage and sets a lean mixture code .....ted

You are almost right on this..........

If you have a missfire that is say ignition related,say a coil is defective and not firing the plug and the fuel/air mixture... You will have an excessive amount of unburned fuel that is pushed out the exhaust....With this you will get first a po300,multiple missfire code. Then if it missfires enough you will then set a code of the cylinder that the coil is defective. IF you drive it long enough with the missfire you could possibly set a Rich condition code. Most cars now will shut down the injectors for the cylinder that is missfiring to save the converter. But the car wil not set a Lean code when there is an ignition missfire.


If you have a missfire and the criteria has not been set to turn the MIL, you can look at Mode $6 info to tell what cylinder is the problem...but thats anouther thread all togther