circuit for sync trigger, efi on an MC-1

[auditude at neta.com]

Hello Audifans,

I was/am about to give up in my quest to get a circuit designed that
will send the timing reference sensor signal to the aftermarket efi
computer only for the compression stroke (MC-1-based motor).
However, I made a little progress, so I'll continue exploring that
option until I either succeed of fail, rather than give up.

Briefly, the issue is that I want to sync the timing of the motor off
the crank if possible, rather than off the cam, which is much easier.
I would be able use the flywheel pin to do this, except that it
passes the sensor both on the compression stroke and the
exhaust stroke.  So, I wanted a circuit that would basically
suppress the signal coinciding with the exhaust stroke.

This is for an efi system that is capable of running direct ignition
and sequential injection, so it needs to have a input coinciding with
a single cylinders compression stroke.

I was thinking I needed basically what would function as an
electronic relay, which translates to a transistor in the solid state
world.  However, after discussing this with an engineer at my work,
we came up with a better solution.

If I use an "AND" gate IC, it's output is only "high" when both inputs
are "high".  So, the timing reference pin passes the sensor, and
nothing happens, unless the hall sensor signal is "also" present.
In operation, the hall sensor signal will be present before and after
the timing pin signal, since it's duration is longer.  The actual signal
sent to the ecu will be the "high" output of the IC.

I guess a difference between this and a transistor/relay type of
concept is that the output to the ecu is not the output of one of the
sensors, simply routed via a normally open circuit.  The output of
the AND gate is discrete from the inputs.  In other words, the
output is generated by the IC, not just conducted by it.

The beauty of this is that no matter how I rotate the ignition
distributor, as long as the output window of the hall sensor overlaps
the timing pin output "at all", then the signal to the ecu is always
accurate and repeatable.

The alternative would be for me to use only the rising and/or falling
edges of the hall sensor output window.  This is what I'll default to if
I an unable to make this circuit.  (I am aware of the fact that I'm
potentially gaining very little by doing all this, but if it works out in
the end, then that's cool.  I like to learn new things and figure stuff
out.)

So, outside of this chip, I need to make a little board with a socket
on it (in case I need to replace the chip), maybe put a 1 micro farad
capacitor across the +/- pins, add some wires off the board, and
put it in a box of some sort.  One person suggested potting the
device to mitigate problems from vibration, but I think that is overkill
<bg>.  Do I need to do that?  I don't think it's going to be vibrating
that much, mounted in the cabin by the new ecu.

I suppose the best way to do this would be to go ahead and
construct the circuit, and then hook it up and spin/run the engine
and observe the output of this circuit to determine if it works and is
usable.  Then provide the specs to the vendor so that ecu can be
programmed to expect this input.

If anyone has any advice or anything like that, I'd appreciate it.  I
am not all that familiar with this type of thing, so I may overlook
something important.

Thanks,

Ken
'85 4ksq MC-1/Linkplus efi project
'88 5kcstq
'94 SL2
'87 5kt parts

p.s.  If I end up using the stock hall sensor output sans this circuit,
I still need to provide specific information regarding the stock hall
sensor output to the ecu vendor.  Apparently to accurately
determine the rising and falling edge information on the stock hall
sensor output, or even the data pertaining to my circuit idea, I need
to physically locate TDC using a dial indicator and a degree wheel?
 Does that sound correct?  I would like to become familiar with the
use of these types of tools, if it is something that will be helpful to
me later (or now).  I got some general