Weird Problem w. Ignition Coil Today

[HOrnbrod]

Heading home today about 1/4 mile from the house and the MJ dies, instantly. It would crank and crank and never fire back up. I walked home, grabbed a spare coil and my meter and drove back with Mama's car. Checked for voltage to the coil, it's there. Check for spark, it's not. Swap the coil, it fires right up. Drove home and pulled out the bad coil (it's a fairly new MSD Blaster coil). The primary and secondary resistance readings are fine and there nothing externally wrong with it. I've never seem a coil go bad before and still test good. I'm snowed. :dunno: Anyone had this problem?

[Geonovast]

Maybe the plug connection was just loose?

 

Have you put it back into see if it would fire again?

[HOrnbrod]

Sure did, a couple of times. It's dead - nothing's getting passed from the primary to the secondary windings, and both are within specs resistance-wise. There used to coil testers around at service garages, I remember using one made by Mallory at a gas station I worked at years ago. Haven't seen any lately though.....

[Geonovast]

I think O'reillys might test coils.

 

What kind of resistances are you getting on the new coil?

[HOrnbrod]

Getting 1.4 ohms on the primary, 12.5K ohms on the secondary.

[Geonovast]

And that's pretty close to the old coil?

[jimoshel]

Once I seen a bad coil test good. '73 Dodge with a 383. Install coil, truck no start. Coil test good, both resistance across primary and secondary. No short between windings. One thing I have noticed. On some coils the windings are connected at the ground end. This seems to have some effect on how they test and work. Also when testing coils, and xfmers with a ohm meter the wire resistance is so low that many meters can't give a accurate reading. You can have a short between windings and a ohm meter won't pick it up. It's been so long since I've done it that I don't remember the exact procedure but the only way to fully test a coil, or transformer is to feed a audio signal in and measure the results with a distortion meter.

[HOrnbrod]

And that's pretty close to the old coil?

 

Yes, both coils tested within specs according to the FSM. The FSM details a coil performance test using a test machine the dealership supposedly has. The bad MSD coil only lasted about six months. Made in China stamped on it. :fs1: You just can't beat genuine OEM parts anymore.......