Ign Advance on MR-2

[Diehl, Jeffrey]

For all fo you who have replied and tried to help me, Thank you.  I'm not
trying to be difficult, but I have to really understand how this system
works.

My dad and I are considering an engine modification which will necessitate
converting to a distributor-less ignition, or at least fooling the ECU into
thinking it has a distributor....

We're thinking that as the tooth approaches the magnet, it induces a current
which gets larger as the tooth approaches and smaller as it passes, forming
(perhapse) a sin wave pattern.  

Now, if the ECU fires a spark plug when this current exceeds a fixed
voltage, we could advance/retard the ignition timing by adding a bias
voltage into this equation.  The fact that the pickup only has two wires
coming out of it implies that all of this math is being done inside the ECU
and not by biasing the pickup itself, right?  These details are important to
us when we try to build a circuit which emulates this behaviour.

Any insight you may have would be most welcome.

Thanx,
Mike Diehl.

-----Original Message-----
From: Chris Conlon
To: diy_efi at diy-efi.org
Sent: 8/11/2001 12:46 PM
Subject: Re: Ign Advance on MR-2

At 12:42 AM 8/11/01 -0600, Diehl, Jeffrey wrote:

>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.

The tach should be run via a signal from the igniter. On an '87 it
probably just takes a signal from the low voltage side of the coil.

>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?

That ECU uses an AFM. It doesn't measure MAP directly, but can figure
out load, based on RPM and the AFM signal. It then uses the load value
to adjust the spark timing. The ECU controls all aspects of spark
timing... except dwell, which is probably controlled by the igniter.

Actually that ECU is old enough that the Ne signal from the dizzy
(the one with more teeth) may go to the igniter, which then feeds a
copy of the signal to the ECU. (Operation is pretty similar to the
other setup, though, from the ECU's point of view.) Just a quirk to
watch out for when you're tracing down wires.

   Chris C.

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