Ign Advance on MR-2

[Programmer]

Check out a 3.0L Chrysler --circa 1988-1992. They ran
optical dissys.

Lyndon.
----- Original Message -----
From: "Diehl, Jeffrey" <jdiehl at sandia.gov>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, August 22, 2001 2:03 AM
Subject: RE: Ign Advance on MR-2


> I've heard a lot of talk about magnetic reluctor sensors and the
associated
> circuitry.  What about a Infra-Red emitter/receiver pair who's output goes
> through a Schmitt trigger?  This seems easier to design around...  What am
I
> missing?
>
> I could have two wheels attached to the crank pulley, one with 1 tooth,
and
> one with 4 teeth.  I might have to run the output through a flip-flop to
> reduce the frequency 1/2...  Then use a 2-bit counter to select one of 4
> transisters to turn on, which in turn charge/discharge the coil.
>
> This seems simple, actually.  Am I missing something?
>
> I can't use the cam gears for timing, because we intend to adjust the cam
> timing on the fly; this is why we need to build a circuit which emulates
the
> distributer, which is run off the exhaust cam.
>
> As you can see, we have suffered from feature creap.  We started out
simply
> wanting to emulate the distributor, now we are talking about a 4-coil DIS.
> <evil grin>
>
> Any comments are more than welcome.
>
> Thanx,
> Mike Diehl.
>
> -----Original Message-----
> From: Les Newell
> To: diy_efi at diy-efi.org
> Sent: 8/12/2001 4:28 AM
> Subject: Re: Ign Advance on MR-2
>
>
> The ouput of this type of sensor is very dependent on engine speed. At
> lower
> revs it will be a sharp positive spike as the tooth leading edge passes
> the
> sensor and a sharp negative spike as the trailing edge passes the
> sensor. As
> the speed increases the waveform becomes more square and at very high
> speed
> the waveform will approximate the shape of the tooth. The wave shape is
> also
> dependent on the load on the sensor.
> The output voltage is also highly dependent on speed. Open circuit
> voltage
> can be anything from a few millivolts at cranking speed to tens of volts
> at
> high revs. The only way to make sense of these messy signals is to
> detect
> the zero crossings as they will always be at the leading and trailing
> edges
> of the tooth.
>
> What are you trying to do? Are you trying to replace the distributor
> because
> you don't have room for it or are you trying to replace the ECU?
>
> If you are replacing the distributor it may be easier to make up toothed
> wheels that can be attached to the camshaft and relocate the sensors.
> The
> toothed wheels could even be replaced by blobs of weld on the cam pulley
> (assuming it is belt drive). Obviously you will still have to make an
> electronic distributor but this should not be difficult. One way would
> be to
> use a set-reset latch driven by two crank position sensors, one for
> piston 1
> at about 10-30 deg ATDC and one for piston 2 at 10-30 deg ATDC. The
> latch
> would then drive substantial PNP transistors, switching the high sides
> of
> the coils (the ECU drives the low side). One coil would then feed pots 1
> and
> 4 and the other pots 2 and 3, using the wasted spark system.
>
> Les
>
>
> > 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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