[TR] Testing ignition coil: what am I doing wrong????

[spamiam at comcast.net]

Randall,

I thin you hit the nail on the head.  I was not getting clean enough 
switching.  I put a condenser across the coil terminals and used a spare set 
of points to do the switching and I got a good spark from the 2 coils I 
tested.

I put an ohmmeter on the 2 wire reluctor connector and got 800 ohms and it 
did not seem to change as I wiggled the wire.

I did not check the resistance to engine ground.  I will have to check that.

Now to go back and check the presence of a spark on the same coil when 
firing it from the HEI module.

My TR7 HEI unit has a capacitor (condenser) on it.  I suppose it is possible 
that it is failing.  Do you know if the HEI system requires a condenser?  I 
will continue to fiddle with the TR7 today.

I have had a coil fail once.  It was an old 1966 original to my TR4A.  It 
may simply have failed from old age, but I suspect that it was killed by my 
sparkplug wires.  I made the mistake of using modern carbon core wires with 
the old original type of cap which spears the conductor.  With motion, I 
think the connection of the spear to the carbon conductor became high 
resistance or intermittent.  I think that this caused very high voltages to 
build up in all the HT side.  I think the insulation broke down in the coil 
due to these excessively high voltages.  I think that those same transients 
got into my electrics and palyed havok there too.  My old original voltage 
stabilizer failed, as did a transistor replacement!  I now use copper core 
wires when I use the original type cap for show, and I use the MGB version 
of the distributor cap with magnecore wires for actual driving.

I also have a Pertronics on the TR4A, but I am considering switching to 
using a Boyer-Brandsen transistorized switching unit with points.  The 
magnet hub of the Pertronics does not fit all that well, and causes the 
rotor to not seat fully.

-Tony

-----Original Message----- 
From: Randall
Sent: Sunday, June 17, 2012 10:57 AM
To: spamiam at comcast.net ; triumphs at autox.team.net
Subject: RE: [TR] Testing ignition coil: what am I doing wrong????

> I did get some
> sparks from the
> ground wire when I broke the ground

Try adding a condenser to the circuit.  Also make sure there is nothing on
the secondary side that could bleed high voltage to ground (like a glazed
spark plug).  The problem may be the way you are breaking the primary
circuit (those sparks are drawing energy out of the coil), but I'd try the
condenser first.

Delco HEI used different kinds of pickups.  If it just has two terminals,
then it is a simple inductor coil.  According to my GM book, the coil DC
resistance should be between 500 and 1500 ohms; and infinite from either
lead to ground.  If it has 3 terminals, it may be a Hall effect transistor.
There is a test procedure given, but it requires applying 12v and a magnetic
field to the pickup.

I also thought coil failures were relatively rare, but I've had 3 of them on
my TR3 in the past 3 years; and the HEI coil on my GM car has been replaced
several times as well.

-- Randall



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