Date: Sat, 12 Jan 2002 13:54:43 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Idle stabilizer
In-Reply-To: <5.1.0.14.2.20020112101016.00a33cc0@pop-server.austin.rr.co m>
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At 12:45 PM 1/12/2002, John Clavin wrote:
>Typically, multivibrator circuits are used to create free-running or
>triggered oscillators. My guess is that in the idle stabilizer they are
>triggered by the sender unit to send the actual ignition pulses to the Hall
>Control unit.
I'm think you're right here.
>The reason for this would be to provide some signal
>conditioning that evens out the timing between individual, erratic pulses
>from the sender. It also would provide some wave form shaping of the pulses
>so as to make them more uniform, and hence more reliable, as seen by the
>Hall Control unit. The net effect would be to take a jittery stream of
>poorly shaped pulses and replace it with a more uniform stream of evenly
>shaped and spaced pulses.
Don't think so. The sender pulses are not erratic -- this is a purely
electronic circuit (the Hall generator). It may do some wave shaping, but
that 's incidental to its true function which is to...wait for
it...stabilize the idle speed, which it does by adjusting signal phase
(timing) on the fly.
>Disconnecting the idle stabilizer by connecting the cables to it together
>merely sends the raw sender signal to the Hall Control unit. If the
>electrical signal from the sender is "clean" because the sender produces a
>good signal and the engine is running smoothly, then it is likely that you
>can run without the stabilizer.
You can run fine without it. However, you lose its benefit, which AFAIK is
primarily to provide good torque at idle speed.
>An examination of the circuit board reveals that the three wires involved
>are power, ground, and signal. I doubt the idle stabilizer itself knows
>much about what the temp senders or O2 sensor are doing. Decisions based on
>those outputs are probably performed in the ECU.
Correct, it has no notion of anything but the frequency of an incoming
pulse stream controlling the phase of an outgoing pulse stream at the same
frequency.
>In addition to the wire from the idle stabilizer, the Hall Control Unit
>connector also has wires which connect to the ignition coil and the ECU. I
>suspect this control unit functions much as an electronic relay, switched
>on and off by the Hall signal, and handling the higher currents involved
>with the coil.
It's a little more elaborate than this -- it provides both the actual
energy and also the shape and duration of the primary input waveform to the
coil (it corresponds to the RLC tuned circuit provided by points,
condenser, coil primary in a standard Kettering ignition, but it's an
active circuit with more direct control over the output). It takes timing
info from the Hall generator (as modified by the idle stab.) but that's all.
> The heat sink it is mounted on suggests it has some high
>power transistors doing this. The wire to the ECU is probably an output
>which tells the ECU what the ignition is doing, although it could be some
>other type of control signal from the ECU.
Should be the tach input to the ECU.
>If the above analysis is correct, then the idle stabilizer is always "on"
>and performing its function when plugged in. I could see no way that the
>ECU or Hall Control Unit could tell it to turn off for a warm engine. I
>suspect that it may seem to turn off because its effects under those
>running conditions are not as critical or noticeable in terms of engine
>performance.
No, it's always on -- however it only exercises control over the timing
within a narrow rpm band. Within that band it exerts a powerful effect at
all times. To see it at work, set up a timing light and watch the timing
bounce around at idle. Remove it (idle stab) and look again -- timing will
be rock-steady.
cheers
david
--
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
