Bad Coil? - Team Camaro Tech
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post #1 of 18 (permalink) Old Dec 7th, 09, 11:54 AM Thread Starter
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Bad Coil?

I made a mistake and switched wires on my Blaster 2 coil (pink and yellow wire on the negative terminal) and tried to start the car a few times. It cranked but did not start and when I noticed the mistake, I switched the wires back to the positive terminal on the coil, but it still wouldn't start. I should have checked for spark but didn't yet. Do you think I fried something? THANKS.
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post #2 of 18 (permalink) Old Dec 7th, 09, 04:38 PM
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Re: Bad Coil?

Hopefully not. I've actually seen them run this way although not very well. Just check for spark, and if you have none hopefully it's nothing more than a blown fuse. If you have electronic ignition, the worst that could happen is the module or box was fried.

These old carberated cars can easily be flooded. Hopefully you resolved the spark issue with the rewire and just have a flooded motor. If you have spark and it still won't fire, try holding the pedal to the metal to clear the flood.

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post #3 of 18 (permalink) Old Dec 8th, 09, 10:51 AM Thread Starter
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Re: Bad Coil?

Thanks Dave. I'll give it a shot this weekend. I'm keeping my fingers crossed!
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post #4 of 18 (permalink) Old Dec 9th, 09, 07:01 PM
 
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Re: Bad Coil?

I have all my coils load tested at places like Auto Zone, that have off the vehicle run testers. I no longer trust resistance testing, load testing runs the coil, off the car, the only way to get accurate results.

Regards,

Milton
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post #5 of 18 (permalink) Old Dec 10th, 09, 11:40 PM
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Re: Bad Coil?

If we consider that a coil is a step up transformer, wiring it backwards shouldn't impact performance at all, although that's theory, not experience.

Its doubtful that it hurt things. Check for spark an move on.

A resistance check of the coil will probably not show more than 4 Ohms or so. Zero or infinite are bad indications.
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post #6 of 18 (permalink) Old Dec 11th, 09, 04:22 PM
 
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Re: Bad Coil?

Reversing the polarity on the primary side of the coil doesn't make it fail, all it does is make the spark travel from the negative electrode to the positive electrode of the spark plug, instead of positive (center) to negative (ground).

Regards,

Milton
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post #7 of 18 (permalink) Old Dec 11th, 09, 08:32 PM
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Re: Bad Coil?

It's not quite as simple as a step up transformer guys. The primary and secondary are connected together on one leg of each winding. So wiring it backwards won't burn it out, but it can induce flyback voltages into the points or ignition module. (I'm sure a breaker point setup would handle it fine) Whether or not anything was damaged is up for debate. But checking for spark is the best first step instead of analyzing what may have been damaged. If there's spark then no harm done.

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post #8 of 18 (permalink) Old Dec 12th, 09, 07:54 AM
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Re: Bad Coil?

X2

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post #9 of 18 (permalink) Old Dec 12th, 09, 09:32 PM Thread Starter
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Re: Bad Coil?

Well I checked the fuses first because that was the easiest and they were all good. Then bench tested the coil, it was a little off spec, MSD Blaster 2: primary resis was 1.2 ohms (MSD spec: 0.7 ohm), secondary resis was 5.1 Kohms (MSD spec 4.7 kohms). According to MSD tech line, coil is good. Checked for spark today, no spark. So I've narrowed it to the ignition module so far. I have a Pro Comp distributor, $15 for a module, it's on order. I hope that's it. I'll keep you all updated. Thanks.
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post #10 of 18 (permalink) Old Dec 12th, 09, 09:59 PM
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Re: Bad Coil?

According to your readings, the secondary resistance is about 8% high. I'd say +/- 10% has got to be good. The primary resistance is about 71% high. However most digital volt meters aren't extreamly accurate at resistances less than about 2 ohms. Those resistance readings are reasonable. Hopefully the module will get you going for cheap.

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post #11 of 18 (permalink) Old Dec 13th, 09, 09:25 AM
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Re: Bad Coil?

X3 Wiring the Coil backward will not harm the coil but will induce Flyback Voltage Spikes that will burnout Transistors in MPC Circuits. I would say your MSD Ignition Module in your Pro Comp Distributor is Burnt.

You might think about installing an Inline Filter for the Ignition Module to protect it in future.

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post #12 of 18 (permalink) Old Dec 13th, 09, 11:57 AM
 
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Re: Bad Coil?

Checking only the resistance is NOT the ONLY way to test the coils any longer, even if that is what MSD "techs" say. A coil can appear perfectly good when cold and resistance tested, even some times when hot, but, when layer shorting occurs, the coil will show it is defective, and most times, layer shorting (the main reason for coil failure) isn't seen until the coil is in run mode, operating temperature.

So, all that hooey about resistance testing just doesn't get the job done any longer. RUN testing them does. In every instance of run testing I have ever done, I resistance tested the coils BEFORE having them run tested, and ALL showed "good" per resistance spec, when only 1 coil out of over 40, was actually still "good". The rest failed when they got to operating temperatures. 3/4ths of them still read "good" when they were actually dead, resistance re-tested at operating temperatures.

I now test EVERY coil I buy, from right out of the box. I take them out of the package IN THE STORE, and run test them first operation, before it and I leave the store. I've run into 9 new defective coils so far, bad right out of the gate, resistance values OK, run test stopped the spark from them.

It is just this simple, rely on an old, outdated method of testing, or, do both, old and new, and get it right from the start, no guessing, no worries, no running around "assuming" the coil is good, when it isn't.

Sorry for the rant, but, it gets tiring reading the same old stuff over and over again, "this guy said this, that guy said that, and the coil checks out, but I still have no spark". Old, real old.

Regards,

Milton
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post #13 of 18 (permalink) Old Dec 16th, 09, 12:48 AM
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Re: Bad Coil?

Quote:
Originally Posted by dnult View Post
It's not quite as simple as a step up transformer guys. The primary and secondary are connected together on one leg of each winding. So wiring it backwards won't burn it out, but it can induce flyback voltages into the points or ignition module. (I'm sure a breaker point setup would handle it fine) Whether or not anything was damaged is up for debate. But checking for spark is the best first step instead of analyzing what may have been damaged. If there's spark then no harm done.
I'm not arguing, but asking for clarification...

There are 3 terminals on a coil. 2 primary and 1 secondary.

P1 would be connected to 12V
P2 to the points, or other switching device leading to ground.
S1 is connected to the spark plug
S2 is grounded internally to P2 theoretically

When I think about it, I don't see it working. When I draw the circuit, I don't see it working.

12V---Primary---Points---Ground
Ground---Secondary---plug gap---Ground

If the grounds are internally connected, the switching of the points doesn't happen

If the 12V is connected to the secondary:

12V---Secondary---plug gap---Ground

things would get ugly.

Maybe a case ground on the coil, but still not internally connected?

Feel free to roll around laughing

Edit: Actually I did some searching and saw a drawing of an electronic ignition showing an internal connection in the coil so maybe my mental picture works for points only. I also saw a drawing for military a points ignition with the condensors (capacitors) in series, which isn't right.

Last edited by 67sc; Dec 16th, 09 at 01:10 AM.
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post #14 of 18 (permalink) Old Dec 16th, 09, 03:33 AM
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Re: Bad Coil?

S2 is not 'grounded', it's just connected to P2.
Points closed (module turned on), current flows through coil, EMF(electro motive force) is generated about primary coil.
Points open (module turned off), current stops flowing, field collapses, secondary winding gets an induced field because of being wrapped about the primary coil, and this induced EMF gets discharged through plug gap.

True, condensor is in parallel to point set, not in series.

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post #15 of 18 (permalink) Old Dec 16th, 09, 11:11 AM
 
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Re: Bad Coil?

Oh, heck, just take the coil down and get it load tested, and stop wasting time and effort with resistance checks that won't tell you much of anything.

Life is way too short to waste doing all kinds of things that won't get it fixed.

Regards,

Milton
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