Ign Advance on MR-2

[Diehl, Jeffrey]

Here's a puzzle, then.  I believe that the 4-tooth wheel indecates when a
piston is at TDC, and the 1-tooth wheel indicates when #1 is at TDC, but,
why are these wheels slightly offset from each other?  Only by a few
degrees, but they do not line up.  Any ideas?

Thanx,
Mike Diehl.

-----Original Message-----
From: Les Newell
To: diy_efi at diy-efi.org
Sent: 8/11/2001 3:45 AM
Subject: Re: Ign Advance on MR-2

Hi Mike,
The ECU generates the advance/retard. The wheel with four teeth is to
tell
the ECU when a piston is at TDC and the wheel with one tooth is to tell
the
ECU when piston 1 is at TDC. From this information the ECU always knows
the
crank position. There is probably a vacuum sensor attached to the
manifold
somewhere. From this information and possibly data from other sensors
the
ECU can work out the optimum timing.

Les


> 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.
>
>
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