Spark timing, '747

rauscher at icst.com rauscher at icst.com
Mon Jan 18 18:22:23 GMT 1999




In a previous post, Bruce mentioned:

>There is a spark adder, called main spark bias, which moves the
>entire table up or down in value.   So lets say your at 0 degrees
>advance with a spark bias of 10 degrees.   If you drop the spark
>bias to 0 then your initial timing of 0 becomes -10.   There are >some engines
that are fussy about the initial timing, and spark
>bias.
>Generally I find alot of engines like 6d initial, a spark bias of 6.
>Now just to really foul things up/and/or confuse them there is a >cold spark
bias.  Normally I have a fair amount there (15ish). 
>Then with the above 16-20d BTDC idle timing. 


>From what I know, for timing:

    Initial advance. This is the physical position of the
    distributor. Set this with timing light with bypass
    disconnected.

    Spark Adder (main spark bias). A location in the ECM mapping?
    Anyone know where this is?

    Cold spark bias. Again, mapping in the ECM?


This all pertains to the '747 ECM.


BobR.

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