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Re: Bad Coil?

To: Malcolm Walker <walker05@camosun.bc.ca>
Subject: Re: Bad Coil?
From: msecres@ibm.net
Date: Thu, 27 Nov 1997 09:10:41 -0800
Cc: triumphs@Autox.Team.Net
References: <Pine.OSF.3.95.971126132538.9916A-100000@ccins.camosun.bc.ca>
Malcolm Walker wrote:
> 
> On Wed, 26 Nov 1997, Bob Danielson wrote:
> 
> > Just had the alternator on my 75 TR6 rebuilt and, it may be coincidence, but
> > the car has started to miss. It did it a little before but rather
> > infrequently. The problem appears to be much worse when the lights and
> > heater fan are on. I've tried the plugs gapped at both .025 and .035 with no
> > improvement. It has a Lucas Sport coil and I'm wondering if it's the
> > culprit. Is there anyway to test it and if it is bad what's the best unit to
> > replace it with?
> 
> I've no idea how to test a coil, but the Moss parts catalogue suggest that
> you check the low-tension lead (under the dist. cap) for signs of fraying
> or breakage.  I don't know if it's on the TR6 dizzy but on the TR4 (and
> many other Lucas dist) it's a cotton-covered wire, relatively thin, that
> goes from the coil leads to the breaker points (it's cotton covered so
> that it can move back and forth with the movement of the advances without
> fatiguing)
> 
> Mine is frayed and will need to be replaced.  If this wire goes bad, the
> car will miss, and eventually cease to run.
> 
> Just a thought...
> 
> -Malcolm

One could go to a local auto parts supermarket and find a spark tester, which 
(though 
I've never used one), is a simple device that gives you a measured look at your 
spark.  
The above problem does sound like "coil" to me -- it gets worse as the coil 
slowly 
degrades.  Just went through this with my GT6.  A large draw on the electrical 
system 
(lights, etc.) might result in less voltage to the coil, only worsening the 
symptoms.  
However, a longer plug gap would definitely increase the symptoms -- although 
the 
difference between .025 and .035 is not that great.  For a simple coil test, 
take the 
coil's output lead out of the distributor, and prop it (without touching) up 
close to a 
valve cover bolt.  Crank the car.  If the spark comes out skinny and yellow, 
think about 
a coil replacement.  With a Lucas Sport, it should be fat and blue.  You will 
also need 
to determine what caused the coil to go bad -- it should be getting 12volts in 
both the 
"start" and "run" keyed positions, since it is internally ballasted ...

--
Martin Secrest
73 GT6
74 Spitfire

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