Are the O2 sensors the problem??

[rock883]

Whenever I start my explorer it puts out a big black spot on the ground, is this due to bad O2 sensors? I also have some bad gas mileage. Where can I get some replacement sensors, how much will they cost me, and where are these things at on my truck? I have a 1991 Explorer 4dr xl if that helps. Any help will be appreciated. Thanks.

 

[Dr.Doug]

No, O2 sensors only do their job when the engine is warm. When the engine is cold it is in the "closed loop" mode and is controlled by the computer's EPROM for richness and not the O2 sensors.

Maybe your fuel pressure regulator is bad or simply your engine is worn and blows oil by the rings or valve guides causing the black marks.

Doug

 

[Dr.Doug]

No, O2 sensors only do their job when the engine is warm. When the engine is cold it is in the "closed loop" mode and is controlled by the computer's EPROM for richness and not the O2 sensors.

Maybe your fuel pressure regulator is bad or simply your engine is worn and oil blows by the rings or valve guides causing the black marks.

Doug