Quote:
Originally Posted by Olympiadis
I have seen an instance where a WAI caused a significant loss in FE. It was an underpowered engine that was needing to do a lot of work, - load carrying and hill climbing. The loss in power from the WAI created a need for so much throttle that PE - Power Enrichment mode was invoked by the ECM, which enriches the mixture to between 11.5:1 and 12.5:1 AFR depending on the model. In this case it would have been extremely helpful to have a driver controlled valve to switch between CAI and WAI.
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That is a very good point. If you reduce engine output to the point where the PCM is in PE mode a lot, your fuel economy will be wrecked.
Also note that some ECMs / PCMs are programmed to richen up the fuel mixture, if the air and/or coolant temperature gets too hot (presumably to prevent pre-ignition).
So there is a break-even point which you can accidentally cross, if you're not careful. That point will depend on the vehicle, and the ECM / PCM programming.