Ign Advance on MR-2

[Diehl, Jeffrey]

I think you've communicated the main problem for me.  I need to understand
how the ECU "knows" the engine position.  

If the ECU were a digital computer, I could imagine a fast clock and a
counter which was latched at the passing of each tooth in the 4-tooth wheel.
This count could be used to calculate RPM and the clock could be used to
trigger the firing of the next injector/sparkplug.  But the ECU in the MR-2
doesn't seem to be that sophistcated.  Looks to be a completely analog
system! 

I guess this same algorithm could be done in analog...  Is that how it
works?

Thanx,
Mike Diehl.

-----Original Message-----
From: Joseph Obernberger
To: diy_efi at diy-efi.org
Sent: 8/11/2001 8:08 PM
Subject: Re: Ign Advance on MR-2



"Diehl, Jeffrey" wrote:

> Hi all.
>
> I'm still learning, so be gentle... <grin>
>
> I've got an '87 MR-2 and I'm trying to figure out how it effects
timing
> advancement.  It has 2 wheels in the distributor, one with 4 teeth,
the
> other with 1.  The single-toothed wheel is probably used to run the
tach and
> is slightly offset from the cooresponding tooth on the 4-tooth wheel.
>
> Now the teeth on the 4-tooth wheel pass by what looks like a magnetic
pickup
> and I presume that this gives the ECM the baseline timing.  However,
it also
> passes by what looks like a small magnet which is attached to the
pickup.
>
> There are no vacuum lines, so it is not doing vacuum advance.  The
only
> moving part is the shaft on which the two wheels move.
>
> So, my question is: How does this mechanism manage to advance the
spark?
>
> Thanx for any input.
> Mike Diehl.
>

Not sure if your question has already been answered - but...The ECU
controls
when the coil fires, and the ECU 'knows' the posistion of the engine.
So as far
as how it physically adjusts the timing:  The distributor is spinning
around,
and the ECU knows where it is and how fast it's spinning...as the rotor
approaches the contact point (say spark plug wire 1), the ECU can fire
the spark
sooner or later as the rotor wipes past that metal contact for wire 1.
Pretty
sure that is how it works anyway!

                                            joeo


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