base / advance timing - TBI/TPI with distributor

[Programmer]

This would explain why timing is so unstable at an idle, and
why EST disabled timing IS stable.
Lyndon.
-----Original Message-----
From: Marc Piccioni <piccioni at cadvision.com>
To: 'gmefi' <gmecm at diy-efi.org>
Date: November 14, 2000 7:44 PM
Subject: base / advance timing - TBI/TPI with distributor


>I have been having a discussion with another gear head about how advance
>timing is calcualated from the reference pulse generated in the
>distributor.
>
>Here is how I described it, and would like a reality check.
>
>Pre LS1 small block chevy firing order is 1 8 4 3 6 5 7 2. Firing occurs on
>90 deg. intervals.
>
>Distributor is set for 0 deg (TDC) advance with the timing connector
>unplugged.
>
>Sequence
>
>1)  # 2 cyl comes upto TDC and a reference pulse is generated, the ecm
>loads a count value into a timer register based upon current RPM and lookup
>table value ( a lower value == more advance, higher value == less advance).
>
>2) timer reaches 0 generates a timer interrupt, ecm issues a fire pulse to
>the ign. module, #1 cyl. fires xx deg BTDC #1.
>
>3) #1 comes upto TDC and another reference pulse is generated, timer is
>reloaded for #8 firing event.
>
>
>
>
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