Spark timing, '747

[Bruce Plecan]

-----Original Message-----
From: rauscher at icst.com <rauscher at icst.com>
Subject: Spark timing, '747
>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?

Yes

>    Anyone know where this is?

yes,  0014, (warm engine)
>
>    Cold spark bias. Again, mapping in the ECM?

yes, 0015
>
>This all pertains to the '747 ECM.
So do my answers
Bruce
>BobR.