My car is a 1989 305 TPI and over the past few months I have noticed an abnormal amount of black soot on the rear bumper directly above the tailpipe. Obviously the car is running rich. However, my car constantly throws an "oxygen sensor LEAN" code.

The engine sometimes hits an RPM wall and will not rev. This is a lean condition.

Can anyone explain this? Is my o2 sensor measuring lean, and then the computer tries to compensate, adding too much fuel, causing my rich condition?

Please help!

 

If the O????2 sensor is bad or the O2 sensor circuit is malfunctioning and the ECM thinks the A/F ratio is lean when it really isn't it will richen the mixture to try to compensate. That will cause a rich condition and the ECM thinks it's a lean condition.

Another possibilty is that an injector could be sticking or leaking. The O2 sensor only measures the A/F ratio on the driver side exhaust manifold. if an injector is sticking or not working on that side that cylinder will be lean. If the ECM tries to correct it the other cylinders will be rich.

Also the ECM or PROM could be bad.

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