Exhaust Leak
 

Ok, I got a question. What kind of effect will an exhaust leak before the wideband O2 sensor have on the air fuel ratio displayed by the wideband controller? I suspect it to read a little on the richer side even though it itsn't. Correct?

I have an exhaust leak and my AF ratios are a little rich, yet when i looked at my plugs it seems like its running a little lean.

i would think it would read lean as fresh air comes into the exhaust

So the AF ratio displayed is leaner than it really is? If that was the case, then my car is running rich.

I doubt there would be any difference in the AFR readings. The pressure in side the exhaust system is higher then atmospheric pressure, therefore no air should enter the system wile the engine is running.

well how come a header leak can cause you to get terrible gas mileage?