Timing jump at idle

[rr]

Some ecms/masks will vary timing to help control idle rpm. Maybe
that is what you are seeing.

BobR.

Bob Valentine wrote:

> I'm trying to figure out why my timing varies +/- about 4 degrees.    I've
> flattened the table for several cells around in gear idle, 625rpm.  MAP
> stays rock-steady at 35kpa.    Injector pw varies from 2.55-2.6ms.  The
> idle is reasonably smooth no surging or misfire, but would be smoother with
> the timing stable.
>
> With the timing connector pulled and a timing light on the crank, the mark
> stays even on 6deg.   The mark moves and follows the scantool with the EST
> hooked up.  I changed the distributor (and module) since the one in the
> motor had a slight bit of end play - no difference, same symptoms.   Plug
> wires are routed as far from the harness as possible.    Disconnected the
> alternator to rule out AC noise, no difference.
>
> Is this "normal" or is something going on?
>
> -> Bob Valentine
> -> bob at tecmark.com

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