Along with other sensors, the ECU uses the output from a properly functioning O2 sensor to trim the air/fuel ratio.

That said, lets say you had a misfire from one or more cylinders due to a fouled plug or bad wire, and assume the fuel delivery to that cylinder is normal. How would the O2 sensor react, rich or lean, and why?

(I know the correct answer)

 

my guess is that the O2 would read rich and lean out the fuel

 

Well, since no one else wants to play, here's the answer...

The O2 sensor doesn't see fuel, it measures oxygen. If the fuel isn't ignited properly, it doesn't burn enough to consume the oxygen in the cylinder. The O2 sensor will see this extra oxygen and think the mix is too lean. This will add more raw fuel to the tailpipe, possibly overheating the cat and definately making your MPG worse.

So, keep this in mind when you troubleshoot fuel problems.

 

I guess since it's an O2 sensor and not a gas sensor that makes sense. good info, thanks

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Perfectionist &raquo;</TD></TR><TR><TD CLASS="quote">Well, since no one else wants to play, here's the answer...

The O2 sensor doesn't see fuel, it measures oxygen. If the fuel isn't ignited properly, it doesn't burn enough to consume the oxygen in the cylinder. The O2 sensor will see this extra oxygen and think the mix is too lean. This will add more raw fuel to the tailpipe, possibly overheating the cat and definately making your MPG worse.

So, keep this in mind when you troubleshoot fuel problems.</TD></TR></TABLE>
That's pretty basic, i'm surprised how many people dont know it.

 

Also remember that at WOT, the entire thing is in open-loop with no O2 input even being consulted, so it's more of an issue at cruise/partial throttle.