Miata Mailing List: April 1996, Message #347
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   From: garrettn@mindspring.com (Norman H. Garrett III)
Subject: Re: Fooling Computer via Temp Sensor
   Date: Sat, 6 Apr 1996 14:58:31 -0500


>1) Has anyone with aftermarket exhaust and intake (eg: Jackson
>Racing cold air) checked if their fuel mixture is too lean?  I
>assume that it is by design...as a pollution-control measure.
>

We did extensive engine dyno work on a 1.6 and found the flapper air flow
meter to still be reading at wide open throttle even with headers, etc. and
the fuel mixture was still a bit rich - so there is no need for more fuel in
this area. It is out of the EPA test cycle "map" in the brain, so it is
fueled very well.

>2) Has anyone tried to richen the mixture by fooling the computer
>with a potentiometer in place of the temperature sensor?  What were
>the results?


Fooled with it a bunch on the engine dyno while watching engine temps, fuel
consumption, air fuel ratios. You can dail in any richness setting you want,
but again, the stock map was not that bad - the lambda reading stays around
88 for the 1.8L engine, the 1.6 did the same - indicating that fuel was not
the limiting factor. Getting more air in or out is the key. The 1.8L
injection system is such a nice set up that it adapts very nicely to headers
and muffler, filters and the like. The 1.6L is no slouch - even with forced
induction, the air flow meter does not bottom out at wide open throttle at
7200 rpm (I know, I was holding the voltmeter against the screaming engine
while it was doing that!)

The bottom line? The basic maps are pretty well optimized. Concentrate on
plumbing to get more air in - the fuel capacity is fine for either engine...

IMHO

Norman G
Miata Magazine