spark and MAP

[Bohdan.L.Bodnar at att.com]

Two types of advance mechanisms are required:  rpm and load.  For the former,
keep in mind that a flame in the combustion chamber takes about 3 ms to burn.
Hence, timing has to be advanced with increased rpm -- otherwise, much of
the combustion will take place in the exhause manifold!  The advance is also a
function of the engine's load.

Timing must decrease as load increases, and increase as load decreases.  This
is because the a/f mixture requirements will change as a function of load.  A
lean mixture will take more time to burn than a rich mixture.  Thus, at heavy
load, a rich a/f mixture is present and the timing has to be retarded.  At
light load, the timing will be advanced.

A MAP sensor is merely a load indicator to the powertrain control system.

Cordially,

Bohdan Bodnar
Lucent Technologies, Inc.