why lean is bad

[jimberg]

I love these dicussions.

"Too lean" is a relative term. 14.7:1 is the stoichiometric air/fuel ratio but it is not necessarily the ideal condition. Stoichiometric basically means that for every fuel molecule there will be the necessary number of oxygen molecules so that when a chemical reaction takes place there will be no fuel or oxygen molecules left. Closed loop mode is when the ECM is trying to maintain an air/fuel ratio that will yield the most power for the amount of fuel consumed.

Adding more oxygen to the reaction than is necessary does NOT generate more heat. The amount of releasable heat energy will be maxed out at the stoichiometric ratio. Adding more fuel to the reaction than is necessary will reduce heat, however.

When you add more fuel than is necessary, the remaining fuel will be vaporized which will cool down the cylinder. A water injection system does the same sort of thing. "Too lean" would be a condition where the heat being generated by combustion isn't being given enough time to disapate between each firing of the cylinder which would cause heat to build up. At high RPMs this heat would build up rapidly. Even though 14:1 is rich compared to the stoichiometric ratio, it would be too lean at WOT and could damage your engine as described by the other posters.