[s-cars] //S4cylinder (#4 cylinder misfire)

[Mark Strangways]

Yes, I suppose one could wrap a few turns of the wire between the POS and coil in around the ferrite clamp as well to add some turns to that transformer.

Mark 
  ----- Original Message ----- 
  From: Paul Gailus 
  To: Mark Strangways ; AUDIJIM at aol.com ; Audi5TurboTech at yahoogroups.com ; s-car-list at audifans.com ; Robert Myers 
  Sent: Sunday, January 22, 2006 12:16 AM
  Subject: Re: [s-cars] //S4cylinder (#4 cylinder misfire)


  Bob is right in that the POS output voltage is pulled
  near ground potential during the few milliseconds
  of "dwell time" when the primary winding of the
  coil is storing energy.
  The critical timing event is when the POS output
  is released from ground in order to fire the spark
  plug. At this point there is a voltage "flyback" of the
  opposite polarity, and this voltage can easily be
  hundreds of volts at the coil primary terminal
  (and POS output). The peak voltage at this point is
  approximately the output spark voltage divided by
  the coil turns ratio.

  Even a few hundred volts is not enough to trigger
  the cheaper timing lights in which the xenon flash tube
  is triggered directly by the spark plug voltage
  (using a fine wire wrapped around the flash tube).
  Inductive timing lights use a ferrite transformer that
  is clamped around a wire to trigger off of the current
  pulses flowing though it, not the voltage. There is typically
  some simple active circuitry and a pulse transformer to
  generate the high voltage pulse needed to trigger the
  flash tube.

  Although the coil input voltage is lower than the
  the coil output voltage (by ~1/ turns-ratio), the coil input
  current is proportionally larger than the coil output
  current (by ~turns-ratio). So an inductive timing light will
  trigger very easily off of the relatively high current pulses
  at the coil primary winding (POS output). This is
  because it's designed to be able to trigger off the
  lower current coil output pulses.

  Paul
    ----- Original Message ----- 
    From: Robert Myers 
    To: Mark Strangways ; Paul Gailus ; AUDIJIM at aol.com ; Audi5TurboTech at yahoogroups.com ; s-car-list at audifans.com 
    Sent: Saturday, January 21, 2006 6:41 PM
    Subject: Re: [s-cars] file://S4cylinder (#4 cylinder misfire)



    The "output voltage of the POS" is zero volts.  It shorts the twelve volts of the primary coil to ground when it is fired by the ECU.  There is a fairly significant surge of current..

    At 07:31 PM 1/21/2006, Mark Strangways wrote:

      *This message was transferred with a trial version of CommuniGate(tm) Pro*
      Wow, I didn't know that the output of a POS was of higher enough voltage to trigger a timing light.
      What is the output voltage of the POS ? Anyone know ?

      Mark