[DeTomaso] Ignition Coil Failures

[Doug Braun]

John

It's wound on an "E" shaped core which allows the use of thicker insulation
on the secondary wire windings.  The thicker insulation allows much higher
voltage output with less change of internal arcing (which is the main
failure in ignition coils).  The price you pay for this design over the MSD
Blaster's concentrically would design is a larger physical size and weight.
The Jacobs coil's larger size also helps to keep the entire assembly cooler.
Coils heat up during operation due to the currents running through their
windings.

To mount my Jacobs coil, MSD-6AL, MSD Tach Adapter, voltage regulator &
solenoid, I fabricated a larger aluminum plate to replace the stock plate
that mounts to the RH firewall.  The ground connection of this panel to the
car's frame (through its firewall mounts) is VERY important as both the MSD
and voltage regulator need a good ground.  Again, this can be easily checked
by looking for a voltage drop between the MSD-6AL's ground and the negative
battery post during operation.

Doug Braun
blue 73L #5505

-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of John Taphorn
Sent: Thursday, September 04, 2008 5:53 PM
To: doug at silicondesigns.com
Cc: DeTomaso Forum
Subject: Re: [DeTomaso] Ignition Coil Failures


Doug, Asa and Larry

Thank you for sharing your thoughts and suggestions.  I appreciate the
insights.

Doug, What makes the Jacobs coil superior?

JT
----- Original Message -----
From: "Doug Braun" <doug at silicondesigns.com>
To: "John Taphorn" <jtaphorn at kingwoodcable.com>
Cc: "DeTomaso Forum" <detomaso at realbig.com>
Sent: Thursday, September 04, 2008 4:13 PM
Subject: RE: [DeTomaso] Ignition Coil Failures


> John,
>
> The MSD tech is correct about too much resistance in the secondary circuit
> possibly causing your coil failures but I doubt very seriously that your
> head to battery ground resistance is the culprit.  A simple Ohms check
> between one of the plug threads in each head to the negative battery post
> would reassure you but I'd be very surprised if you found more than a few
> Ohms for a reading.  This test would of course require long enough test
> wires for the meter to reach both points.
>
> Cylinder head to ground resistance is insignificant in comparison to the
> typical 100-300 Ohms in a resistor plug and the 1000 to 15,000 Ohms in a
> typical radio noise suppression type plug wire.  What stresses a coil is a
> secondary resistance well above 30,000 Ohms, very wide plug gaps (.055 or
> wider), or a break inside an ignition wire.  High secondary resistance
> leads
> to electrical arcing within the coil which results in shorted windings.
>
> I'd recommend you do an Ohms check on each of your plug wires and your
> coil
> to distributor cap center wire.  Each of the 9 wires should measure no
> more
> than 1000 Ohms per inch.  If any exceed this spec, replace them.
>
> I'd also recommend you do an Ohms check on each of your spark plugs and
> replace any that read open or well above the others.  This measurement
> should be made on each spark plug between its bullet tip that engages the
> plug wire terminal and its small ignition tip surrounded by porcelain (not
> the ground electrode near the tip.  You should see less than 300 Ohms.
>
> When I was putting my ignition system together 15 years ago, I'd heard of
> other owners having MSD blaster failures so I chose to use a better
> quality
> coil which has been running fine on mine for 15 years now.  Like the MSD
> Blaster it's specifically designed for use with capacitive discharge
> ignitions but it is very high quality.  An updated version of the coil I'm
> using is available here:
>
>
http://store.summitracing.com/partdetail.asp?autofilter=1&part=JAC%2D380876&
> N=700+115&autoview=sku
>
> Good Luck,
>
> Doug Braun
> blue 73L #550
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> [mailto:detomaso-bounces at realbig.com]On Behalf Of John Taphorn
> Sent: Wednesday, September 03, 2008 7:01 PM
> To: detomaso at realbig.com
> Subject: [DeTomaso] Ignition Coil Failures
>
>
> The Space City Chapter recently helped me diagnose an RPM related
> vibration
> in my engine.  I noticed the vibration after installing the new roller cam
> in my engine.  It started around 2400RPM and grew worse until about
> 3000RPM
> and seemed to trail off after that.  Fortunately, It sounded like a
> misfire
> to Dan Mixon and this helped us diagnose it; although others, including
> me,
> at first thought it mechanical related.
>
> My initial thought was that it was an unbalance caused by the double disc
> clutch pack. It is a big unit that I always thought would be difficult to
> fully balance and could only assume the shop had done it correctly.
> Accelerating a longer story, it ended up that it was the MSD Blaster 2
> ignition coil.  This is the second MSD coil I have had fail.  Admittedly,
> it
> may be my fault.  On more than one occasion I have inadvertently left the
> ignition switch on without the engine running.  Also, my start routine
> includes turning the ignition switch to "on" and allowing about 30 seconds
> for the Accusump to prelube the engine before starting the motor.  I may
> be
> frying the coil with these actions.
>
> I understand that on a conventional point ignition, if the points happened
> to be closed, turning the ignition "on" without starting the car could
> burn
> the points and overheat the coil.  However, I didn't think that to be the
> case with the MSD mag distributor and 6AL.  Perhaps I am wrong, and I have
> been cooking the coils.
>
> MSD has a Forum at the website that has a troubleshooting section.  Not
> surprisingly, they describe their coils as sturdier built and more
> reliable
> than competitor's coils.  The technician says that the reason coils fail
> are
> generally because of too much resistance in the secondary circuit.  This
> includes bad sparkplug wires with too much resistance, plugs and
> inadequately grounded heads. They elaborate on the importance of grounding
> the heads to each other and the block and then directly to the battery,
> not
> the chassis.  This theme seems to surface often when they review failure
> causes of other ignition components as well. I would think the head bolts
> would adequately ground the heads to the block.  However, I doubt many
> Panteras ground the heads or block directly to the battery due to their
> distant proximity.
>
> I am already employing an additional ground strap from the starter bolt to
> another chassis stud.  Yet, now I am considering running an ~ 6 gauge
> cable
> from the heads to the stud in the front trunk where the battery grounds.
> It
> would be relatively easy to do.
>
> I am curious of other's thoughts on the importance of grounding the engine
> to the battery and whether they have addressed it?  Anyone else with coil
> issues?
>
> JT