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

Richard J Lebens
Mon, 16 Sep 2002 11:06:36 -0700 (PDT)

I'm confused.

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

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?

--- Ben Swann <> wrote:
> Subject: 2111 code on 97 5ktq
> Doyt,
> You will not find the information on exactly how the Reference and
> Speed
> sensors operate in the Bently.  I have the qlist in copy here so that
> any
> others knowledgable of the MAC-11 ECU internals operation would add
> anything I've left out or is in error.
> Information here is gleaned from AUDI service training guide which
> provides
> some of the details of the speed sensor, RPM sensor and Hall signal
> and how
> these signals are used an interoperate.  Probably the actual
> operation with
> repect to ECU internals is in some obscure engineering document.
> Anyway, in short, the speed sensor as it is called is a magnetic
> pick-up
> which produces 135 pulses per engine revolution - 1 pulse/ flywheel
> tooth.
>  The pulses are used by the control unit to determine engine speed
> and the
> ignition timing point.
> The reference sensor senses a pin in the flywheel and generates a
> pulse - 1
> pulse per crankshaft revolution at 60 deg. BTDC,  This signal is used
> by
> the control unit along with the Hall sensor in the distributor to
> identify
> TDC for #1 cylinder.
> The reference and speed sensors are located right next to each other
> and
> AFAIK usually replaced together.
> The Hall sensor sending unit in the distributor produces one broad
> signal
> (square wave) per each distributor shaft rotation just before
> ignition TDC
> on # 1 cylinder.  Only this signal permits the 60 deg. BTDC signal to
> be
> accepted as a reference mark signal in the control unit.  If the Hall
> wheel
> is out of it's window, the signals are ignored, a code is generated
> and the
> engine won't start.
> Once the engine is started, the reference sender pulse is ignored
> AFAIK and
> the Hall signal determines spark/RPM.  I am not sure about the speed
> sensor, but it appears to help keep the signals in sync. while the
> engine
> is running.   The reference sender is required therefore for the
> engine to
> start, and is initially syncronized with the speed sensor and Hall
> window,
> so my best guess is they are all needed for the engine to start, but
> once
> running, only the Hall sensor is actually required (except perhaps to
> resync the signals) - I don't know/just an educated guess.
> I have seen where the engine can be mad to run when the RPM and Speed
> sensor signals aren't present but the fuel pump relay wire(pin 21 on
> connector) is wired to ground - aka the charlie mod which disables
> overboost cutout.  I think this is because the ECU requires the
> sensor
> pulses to be present in order to operate the fuel pump.
> What this boils down to is that your engind will run without proper
> speed
> sensor signal, but it is a good idea to replace it, because the
> engineers
> must have had a good reason to have it.
> Ben
> Subject: 2111 code on 97 5ktq
> Hello listers.......a question about code readings.
> 2111 indicates "RPM sensor signal not getting to Mac 11C ECU in my 87
> 5ktq."  Yet my speedometer and tachometer work just fine, as does the
> dash
> computer.  I think suspect that each of these components depends on
> that
> same RPM signal.   ....but maybe not.
> If the above is true, and if my ECU isn't receiving an RPM signal,
> that
> would indicate that the wire between the signal generator and the ECU
> is
> broken.  (but not broken to other locations such as tachometer and
> dash
> computer?)
> Or, Do those components run off some other signal?
> If all these components run off the same RPM sensor signal, and some
> of
> them are getting that signal, then I can conclude that the RPM signal
> generator (sensor) is functional and does not need replacing.  But
> I'm not
> sure that they all run off the same sensor. That is my first
> they?
> My second question asks how the ECU _uses_ the RPM signal. Does the
> signal have anything to do with the way the ECU handles starting, or
> how it
> adjusts timing or fuel delivery or boost?
> I've studied Bentley on this, and need a little reassurance about the
> above
> details.
> Doyt Echelberger
> 87 5ktq in OHIO   USA

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