Date:         Wed, 1 Oct 2003 00:58:31 -0400
Reply-To:     Alex Towner <altowner@COMCAST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alex Towner <altowner@COMCAST.NET>
Subject:      The details of Motronic
Content-Type: text/plain; charset="iso-8859-1"

The following post from a couple of days ago leads me to a few questions:

 Date: Mon, 29 Sep 2003 12:12:12 -0700
From: Robert Keezer <warmerwagen@HOTMAIL.COM>
Subject: Re: The "Other" System: Motronic (long)

Individual spark timing:

The ECU controls spark timing and calculates this for each plug individually
making for very precise ignition timing.
Minor variances such as plug gap and wear can be compensated for . This
translates to mean that one plug may get a slight ly earlier or later spark
to compensate for any variance.


Knock control:

The Motronic control unit has accurate information on crankshaft position
and firing order so it is possible to determine which cylinder is
knocking(one cylinder usually begins knocking before the others) Further,
circuits operate at such speed that ignition timing can be retarded only for
the knocking cylinder, and advanced for the firing of the next cylinder.
Each knock signal can modify timing in milliseconds.


1) how is it possible for a Motronic computer - on a car with a distributor - to adjust the spark timing for each cylinder independently? The ignition rotor passes a  contact for a given cylinder on the distributor cap, which in turn sends voltage to the spark plug for that cylinder - we all know this. How could the computer adjust this mechanical process for an individual cylinder? It can't adjust the relationship between the rotor and the distributor cap, and there is no electronic regulating system interfering with the ignition wires before they reach the spark plugs. The computer can adjust the timing of the entire distributor, by changing when electrical energy is released inside the distributor via the hall sensor, but it doesn't seem like it could possibly do that once for each spark plug with each revolution of the rotor. I can understand how an engine with individual coils for each spark plug could regulate the timing for each cylinder independently, but not one with a conventional distributor.


2) The same thing makes no sense to me with respects to knock control. If knock is detected anywhere on a distributor equipped engine, I would think the only thing the computer could do is adjust the timing for the whole engine by altering its signal to the distributor. I don't see how it could adjust cylinders independently. In this sense, it would seem it makes no difference which wires from the computer are attached to which of the two knock sensors. If knock is heard anywhere, the timing for the whole engine will be adjusted.

Comments?