Bad coil?

[Anonymous]

I got into my 1962 Comet today and started her up to find to my dismay that she ran terribly rough and died shortly after. I also noticed my tach wasn't indicating RPM. I looked under the hood and found no disconnected or burnt wires. I checked under the distributor and found no cracks or burns or liquid or corrosion. Everything seemed fine. She had been running perfectly 2 weeks before. My battery is a brand new Interstate, I have an electronic ignition swap and a MSD coil. I'm thinking I have a bad coil because the tach is only connected to ground and the coil. Could it be something else? Any suggestions?

 

[addo]

Just check it with a meter, to be sure. You need continuity between the two screw-on terminal, and continuity between the centre socket and the coil case. If you get a solid reading for each, the problem lies elsewhere.

Regards, Adam.

 

[turbocharged66stang]

i could be your pickup coil also your tach gets its signal from it and so dose the coil. you mite also make sure that the weir going to the tach dos not have a bad spot in it and grounding its self. Inspect all the weirs close because you never know when thermite be a hungry mouse around they like weirs. One more thing it cold also be that the brain box gave up.

 

[66200i6]

Measuring Internal Resistance of an Ignition Coil

When measuring resistance, be sure that the contact between the probes and the circuit is clean. Measure resistance in the primary and secondary coils when the coil is hot and cold.


1. Set your meter to ohms.

2. Touch the probes to the positive and negative post connectors on the edge of the coil to measure resistance in primary windings.

3. Observe display. Resistance should be less than a few ohms.

4. Touch common (negative) probe to the coil wire connection and the positive probe to the positive post on the edge of the coil to measure resistance in secondary windings.

5. Observe display. Resistance should typically be about 10K.

Good luck, Ric.

 

[61Futura]

Or maybe the bad tach is screwing up your ignition by drawing current from the coil. Or the wire to your tach is starting to ground out somewhere. I'd try disconnecting the tach wire at the coil and see if the engine runs okay again. I'll keep my fingers crossed for you. I use a timing light on the coil Hi-V wire to look for misfires. A dwell meter on the coil gives valuable info when you have points and I assume it should give a reading for electronic ignition as well. Just some passing thoughts.

 

[Anonymous]

I recently had a coil go bad on me and it was hard for me to diagnose until it finally broke for good. Coils seem to have a tendency to break when they heat up and then be ok once they cool down.

One of the things that helped me diagnose my coil was that I put my timing light on the wires and nothing was coming out. I put my timing light on the wire from the coil to the distributor and nothing came out. There was voltage to the points.

The final deciding test was to test the resistance internal to the coil just as Addo said. I think he suggested it to me. Make sure you check both resistances of the coil. If you get a relatively low reading you are probably ok but if there is an infinite resistance and you are testing the right thing then yeah you are right the coil is your problem.

Good Luck. I know I was glad when I quit breaking down on the highway. And at stoplights. And where ever else the car felt like it.

-Dan