7747 spark control questions.

[rr]

Kevin R wrote:

> In trying to understand this a little more I have a few questions and
> suppositions. Need you guys to yea, nea or just plain shoot hole thru them
> for me..
> Thanks.
>
> Initial spark advance: Lets the ECM know what the dist is set at physically,
> but all the bins I've checked seem to be set at 0.. does this mean those
> application(all trucks) dist are set at 0 physical from the factory or have
> I got what this does wrong?

Yes, they are set to zero degrees. No, you do not have it wrong. An engine
that has additional cam timing, may benefit from additonal static timing.


>
>
> Warm Bias (main bias in TC): Just so neg advance can be applied in spark
> table as pos numbers!? Why is this necessary? If the dist is set at 0
> physical why would neg numbers be needed in main table?

Don't know why. It's just done that way. I tend to set this value at zero. That
way, the table is 'what you get'.

>
>
> Cold Bias: So neg numbers can be applied as pos numbers in coolant(engine
> temp) compensation table. I can see this, but is this table(would think so)
> always active?  Then it would seem both Cold and Warm bias' are active all
> the time!?

Yes, active all the time. Most bins have the typical coolant area set to the
cold bias value. In this manner, the coolant table/coolant bias, has no effect.
Take a look at various bin's, it can help to get a feel for the GM tuning.

>
>
> PE spark: Trying to compare this to a function in a mech dist(I know the
> elect always for more specific spark control) the only reason I can see for
> this is either to use lower numbers in main table for emissions reasons and
> add it back when needed for acceleration or like the PE enrichment to get
> some spark going faster than would happen waiting for a value lookup???

Actually, there is no PE function in a non-ecm distrib. The carb will have a
'power valve' of some nature. However, it is not tied to spark.

On an ecm controlled engine, additional spark is typically tied to additional
fuel. A spark-only ecm system can be tuned to a carb setup. Just add additional
tining at the same map value as the carb goes into enrichment mode.

BobR.

>
>
> Kevin R
>

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