At 03:04 PM 1/12/2002, John Clavin wrote:

>Dave - Thanks for the elaborations, but I'm not sure what you are saying
>if you mean something different here. What do you mean by "adjusting the
>signal phase (timing) on the fly"? That can only be by adjusting either
>the pulse width itself or the timing of individual pulses relative to the
>triggering incoming pulse. What is the purpose of adjusting the phase of
>the outgoing pulses if not to produce a more uniform pulse train. Or am I
>missing the point? What is the signal phase of the outgoing pulses being
>referenced to? Please explain.

Over its operating rpm range, it actively advances or retards the output
pulses (to the ignition controller) relative to the input pulses from the
Hall Generator, so as to maintain a stable idle speed of either 800 or 900
rpm (+/- 50) depending on whether it's the green or the black unit (ref.
24.19).  Calling it phase was probably misleading, since it's a pulse train
and not a continuous wave.

>Providing torque seems to me to be a secondary benefit. Isn't he primary
>purpose to provide for better ignition timing control which results in a
>smoother running engine, hence more torque? Are you suggesting that even
>if the engine runs well without it at idle, that disconnecting the IS
>still reduces the torque available to accelerate from a dead stop?

Sure, because when the engine pulls a load and starts to slow down (from
idle) it advances timing to speed it up again.  Incidentally, if properly
set up the controlled idle speed is 50 rpm higher than the uncontrolled.

There may well be emissions implications, I dunno.

>Interesting. I had not about how it might be limited to control only over
>an rpm band. Certainly the observable effect is as you described, but do
>we know if the circuitry is actually designed for a specific rpm band or
>whether its effects are just more observable at the lower rpms?

Rev the engine and watch the timing smooth out as speed increases...

>  Regardless, it is still active, "on" circuitry at all rpm's and
> therefore subject to causing problems at all rpms when it begins to fail,
> which is really the point I wanted to make.

Absolutely.  It can blow at any seam...

d

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"