Symptoms of a bad coil

[DaGr8Tim]

I was wondering if somebody could list the basic sympotoms of the famous ford coil on the block that goes bad from years of heat expouser.

I'm helping my uncle tinker with his 81 stang with a 73 200. We suspect that it's the coil, because it runs great when cold and is a dog when warm. Also doesn't like to start when warm.

It appears to get fuel at all times. We havn't checked any voltages, but when you turn the key after it's warm it clicks like a bad battery or starter relay. The battery, the alternator, plugs, wires, cap, rotor, distrubitor, starter are all new. Basically the coil is the only part of the ignition system that has not been addressed.

 

[Anonymous]

FWIW, I've always moved the coil to the inner fender near the distributor on all the cars I've worked on. You can even use the original bracket, just get some self tapping screws and a drill. Might work for you. But typically when the coil overheats, it will just stop working... It won't keep the starter from cranking the engine over though.

 

[61Futura]

It has to be one of these:

Battery, starter, solenoid, ground to engine, battery + cable, wire from starter to solenoid. Plus the ignition switch, wire from ignition switch to a small post on starter solenoid, hot wire from solenoid/battery + cable to ignition switch, they all control the solenoid. The solenoid must be mounted to a good ground to work. All four posts of the solenoid should have +12v with the key turned to start. The metal frame of the solenoid should be at ground.

Time to break out the voltmeter and find out if the 12 volts is making it to the starter. It takes some help with someone operating the key. Start checking for voltage at the starter and work your way back to the battery clamps and posts.

 

[DaGr8Tim]

It has to be one of these:

Battery, starter, solenoid, ground to engine, battery + cable, wire from starter to solenoid. Plus the ignition switch, wire from ignition switch to a small post on starter solenoid, hot wire from solenoid/battery + cable to ignition switch, they all control the solenoid. The solenoid must be mounted to a good ground to work. All four posts of the solenoid should have +12v with the key turned to start. The metal frame of the solenoid should be at ground.

Time to break out the voltmeter and find out if the 12 volts is making it to the starter. It takes some help with someone operating the key. Start checking for voltage at the starter and work your way back to the battery clamps and posts.

Thanx for the advice. The car does not have the original ignition lock. It may be a short there.

I'm confused as to why it only happens when it's warm. Not when it's sat over night.

 

[Anonymous]

isnt that "heat sink"?...

the carb gets too hot and the fuel doesnt something or other...

that seems to be common on our I6's

 

[Anonymous]

Poor grounding can lead to high resistance in the connections, which in turn leads to less available voltage and sometimes increased heat across the connection. As the connection heats up, some may shift or separate as things expand. Couple all this with less available voltage, and you may not have enough juice.

 

[Anonymous]

Does your car have a DuraSpark I or II distributor? If so, that could be your mysterious problem. I've read those things go bad over time, particularly since they are near the engine. Like the coil, it too would act up if it was too hot.

The good news is it's only a $35 part at NAPA, and is probably worth replacing anyway.

If you don't have a DS, then this probably won't help you.

 

[DaGr8Tim]

We got it fixxed today. The best part is that it didn't cost a dime.

Upon closer inspection the insulation on the starter wire was cracked and it was touching (just barely) the side of the block. Moved the wire, and taped it up. We'll see it this fixxes the problem.

Thanx for the advice guys.

 

[61Futura]

If that was the problem, you were pushing huge amps through the solenoid. It may have damaged the contacts and start acting up again. It probably won't care if it is hot or cold though.