AW: Ignition Coil

[Aeschlimann Peter KSSG_AI <AI5@domain.elided>]

Dave

I found a simmilar problem with my 76 auto Stag. However the rev needle
was only trembling sometimes beetween 3000 and 4000 rpm on highway
drive. Meanwhile I replaced the dual breakers with a Lumenition and the
problem is away. May be this helps.

Regards Peter
Walzenhausen Switzerland

1976 Auto Stag
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  Peter R. Aeschlimann        Mail : ai5@domain.elided
  Kantonsspital St. Gallen    WWW  : http://www.kssg.ch
  Abteilung Informatik        Tel  : +41 (0)71 494 23 23	
  CH-9007 St. Gallen          FAX  : +41 (0)71 494 28 90	
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>Von: 	David Kirk[SMTP:david@domain.elided]
>Gesendet: 	Samstag, 14. M�rz 1998 21:07
>An: 	Mike Wattam
>Cc: 	TSR stag digest
>Betreff: 	Re: Ignition Coil
>
>Dear Mike and other respondants.
>
>The ignition coil thing is something I discovered whilst trying to get my
>Rev counter working properly. The engine currently runs fine, cold starting
>and all. I have tried shorting the ballast resistor and notice no change in
>either running or starting performance. The problem is the rev counter.
>
>At present the rev counter is extreamly internittant in operation. Most of
>the time it reads zero.
>
>I have had the thing to bits and checked it out internally and can see no
>problems.
>
>I have reset all the ignition timing using strobe lights and oscilloscopes
>to set the dwell angle and pride myself it getting it all spot on.
>
>So why doesn't the rev counter work all the time?
>
>Is it perhaps that the coil is 12v rated and not 6v?. 
>
>My thinking this far is this.
>
>The rev counter works by passing the feed line to the coil through a
>torroid, thus making a simple pulse transformer. Every time the points in
>the distributor open and close the current flow changes in the primary of
>the ignition coil and thus, as the current changes, it exites a current to
>flow in the secondaries of the rev counter.
>
>Now, if this is all true, and everyting was set for use with a 6v coil,
>then when using a 12v coil the current flow should be less, and as such,
>perhaps not enough to exite the required amount in the rev counter!
>
>I have previously tried increasing the number of turns that the coil feed
>wire makes through the torroid primary (initially only one, and I tried 2).
>Thinking about this now I think I need to decrease the number of turns (not
>possible as it has only one as standard) ) or increase the current in the
>ignition coil - by fitting a 6v coil and using the ballast resitor (like
>the way it was made to begin with).
>
>If anyone has managed to follow my irrational and unlogical thoughts enough
>to comment upon my thinking, they would be greatly appreciated.
>
>
>Dave Kirk
>
>----------
>From: Mike Wattam <101714.1343@domain.elided>
>To: David Kirk <david@domain.elided>
>Cc: TSR stag digest <stag-digest@domain.elided>
>Subject: Ignition Coil
>Date: 12 March 1998 21:52
>
>Hi David
>
>Ref your query about ignition specifications;
>
>All Stag coils should be 6V.  While the engine is running, the external
>ballast resistor (Mk1) or a resistor wire built into the loom (MK2) cuts
>the battery voltage by approximately half, so that a 6V coil gives
>sufficient high tension current to keep the spark plugs happy.
>
>I should imagine your car has a 'Sparkrite' coil fitted because it has (or
>once had) Sparkrite electronic ignition fitted.  Check this out first.  You
>may find this coil has a LT to HT conversion rate higher than standard
>coils - that is it may be capable of a higher HT voltage than normal.
>
>The ballast resistor/resistor wire is short-circuited during starter
>operation via the ignition switch, so 12V flows into the coil and doubles
>the normal output to give what is potentially a huge spark, thus aiding
>cold starting without thumping lots of pollution out of the tailpipe end.
>
>In practice however, two things happen which make this theory less than
>highly effective.  The coil will only put out enough volts to give the
>minimum spark, so this feature is really only useful when the plugs are
>worn out or sooted up and a very high voltage is necessary to bridge the
>gap.  Second, if the HT leads are old, the plugs bad or the distibutor
>cap/rotor arm is less than perfect, a lot of tracking across to earth
>occurs and nothing gets to the plugs.  In fact a very high potential
>voltage will increase the possibility of 'tracking' under adverse
>circumstances.
>
>If you use a 12V coil with the resistor still connected, the maximum
>achievable voltage may not be enough under adverse conditions as mentoined
>above.  REmove the resistor circuit and you will get sufficient volts for
>normal running and for normal starting, but again in adverse conditions it
>may not be enough.
>
>As a footnote, let's dwell for a moment on the subject of electronic
>ignition.  If you think about the fact that the HT circuit will only
>produce sufficient voltage to make a spark, the many claims that starting,
>fuel consumption etc will be improved, is a complete myth.  Electronic
>ignition is alleged to improve cold starting by giving out a very high
>voltage, but the Stag with it's 6V coil does this anyway.  So, I believe
>the only real advantage given by electronic ignition on the Stag, is to
>give an excellent idle quality which can be difficult to achieve with
>old-fashioned 'points' - this assumes your electronic ignition has a rotor
>'paddle' to transmit current at the right time (some systems still use the
>old 'points').
>
>I've still got the standard system for the last 25 years, if I remember
>right I am on my fourth set of points, leads and distributor cap.  I would
>classify my idle as reasonable, and top end power is superb with loads of
>grunt through 6,000rpm.
>
>Mike Wattam
>Triumph Stag Register
>
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