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Designer King
Join Date: Mar 2004
Location: Toronto, ON Canada
Posts: 5,499
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FYI: Just a Note re MSD Coil Wiring Failures
I've had an MSD 6AL for about 4 yrs/13000 miles. Soon after I had it installed, the crimp portion of one of the 2 wires that connects to the coil failed, resulting in the ignition cutting out. I could see the wire loosely attached to the connector, resulting in an intermittent contact. Redoing the connection fixed it.
A few days ago, the other connection failed in the same way. This was harder to diagnose, since the connection was covered by the plastic sleeve, so it was not as visible as the first one. Pulling back the sleeve revealed the problem. Just a note of caution. Even though these are not the high tension plug/coil wires, my helper got quite a shock from the poor connection during troubleshooting. So check those wires and connections, and do so w/ the ignition off.
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Paul Yellow 77 Sunroof Coupe/cork interior; 3.2L SS '80 engine/10.3:1/No O2; Carrera Tensioners; 11 Blade Fan; Turbo tie rods; Bilstein B6; 28 tube Cooler; SSI, Dansk; MSD/Blaster; 16x7" Fuchs/205/50 Firestone Firehawk Indy 500s; PCA/UCR, MID9 Never leave well enough alone |
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07-23-2009, 07:01 AM
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AutoBahned
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the coil stores energy
so just turning the ignition off and then messing with it cans till give you a big surprise -- but it is a great way to really learn that there is more to electrical circuits than Ohm's Law... |
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07-23-2009, 07:45 AM
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Designer King
Join Date: Mar 2004
Location: Toronto, ON Canada
Posts: 5,499
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Good to know. Thanks.
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Paul Yellow 77 Sunroof Coupe/cork interior; 3.2L SS '80 engine/10.3:1/No O2; Carrera Tensioners; 11 Blade Fan; Turbo tie rods; Bilstein B6; 28 tube Cooler; SSI, Dansk; MSD/Blaster; 16x7" Fuchs/205/50 Firestone Firehawk Indy 500s; PCA/UCR, MID9 Never leave well enough alone |
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07-23-2009, 07:52 AM
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Registered
Join Date: May 2003
Posts: 3,346
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Actually the coil doesn't store any energy unless it has current flowing through it. The coil works by having a high current flow through it until the points open. Then the magnetic field colapses and causes the energy in the field to be discharged through the spark plug. In a car with a CD ignition the coil just works as a transformer, stepping up the voltage to jump the gap in the spark plug.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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07-23-2009, 08:19 PM
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Designer King
Join Date: Mar 2004
Location: Toronto, ON Canada
Posts: 5,499
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Thank you for that. This appears to have been borne out by the fact that there wasn't a shock w/ the ignition off.
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Paul Yellow 77 Sunroof Coupe/cork interior; 3.2L SS '80 engine/10.3:1/No O2; Carrera Tensioners; 11 Blade Fan; Turbo tie rods; Bilstein B6; 28 tube Cooler; SSI, Dansk; MSD/Blaster; 16x7" Fuchs/205/50 Firestone Firehawk Indy 500s; PCA/UCR, MID9 Never leave well enough alone |
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07-24-2009, 05:24 AM
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AutoBahned
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I agree that the energy stored will decay with the magnetic field collapse -- but how fast it does so is another matter. I would wait a moment before messing with it, esp. if you use a remote switch at the back of the car as some do.
Additionally, most ignitions will have some capacitance and that is connected also. |
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07-24-2009, 08:36 AM
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