code dump - code 2111 speed sensor + RPM & Hall interoperation

[Ben Swann]

There is indeed a knock sensor, which in conjunction with the Manifold
Pressure is used to advance and retard timing.

The ref. sensor sees 2 pins separated by 60 deg. just before and after TDC.

Using the flywheel teeth to get pulses from speed sensor, the two work in
conjunction to know when to expect the Hall signal.  That is for starting
and yes, for knowing when to expect the next Hall signal for appropriate
cylinder.  As best as I can tell they get the ECU to clock with respect to
the Hall signal.

Then the base timing is set and the engine runs with only the requirement
to see the hall signal, since now the pulses are clocked at regular
intervals by the ECU based on the Hall signal.  At least that is my
understanding.  I could be way off as I'm reading between the lines of a
technical training guide.

The diagram I have shows the clocking with 2 reference sensor pulses, with
 60 deg. of crank revolution
between the pulses.    The initial pulse is somewhere BTDC and the second
is ATDC.  That must be why the Hall pulse needs to be in this window.

I believe the reference sensor signal is not used once the engine is
started, but I really don't know for sure.

Regarding the speed sensor, The AUDI tech. ref. I have says:  The flywheel
tooth impulses are used by the control unit to determine engine speed and
the ignition timing point.

I suppose this means that the speed sensor is critical to proper operation
after all.   My guess is that the ECU resynchronizes its clocking every so
often using these signals.  I really don't have any more information
regarding how ECU utilizes the pulses after start, so take what I deduce
with a grain of salt.

If anyone has another reference to provide some clarity, fill us in please.

Ben

[I'm confused.

Reference sender tells ECU TDC cyl #1 intake/exhaust or comp/power
stroke.

Hall sensor narrows it down to comp/power stroke

Rpm sensor ????  I thought it was a fine tune and tells when to fire
Cyl #2 - #5.  Anyone know what the reference is for TDC?  Does the ECU
synthesize the frequency to fire the remaining plugs?  Since you can't
set initial spark timing is it all based on an adaptive control scheme
using the knock sensor?  Did an 87 even have a knock sensor?]