coil on hei distributor

what could be the signs that a coil on an hei distributor is going bad.
ive ask several people who could not tell me. thanks rd

Coil problems are hard to diagnose because they are very similar to other problems that cause a weak spark, like bad plugs, wires, cap, rotor etc.
Try pulling a plug, attaching the plug wire and grounding it to the side of the engine. Have someone crank the engine over and look at the spark. It should be fat and blue. If it looks very weak or faint, you might have a bad coil, or it might be any of the other things mentioned.
Bad coils also have a habit of working poorly when the engine is warm. When it's cold, they produce a good spark.

magicrat,thanks for the coil info
rdobbs

What is the engine doing that you think your coil is bad? Rat is correct that there is a whole host of stuff that "sounds" like a bad coil. Rotors, pickup coils, etc. He is also correct that once the engine gets hot, a crack in the Cap, or Rotor will get worse.

Engine losing power when accelerated,put new cap and rotor,plugs,wires,ign mod, and no change. I know nothing about coils,was just wondering if it could be going bad.

Engine losing power when accelerated,put new cap and rotor,plugs,wires,ign mod, and no change. I know nothing about coils,was just wondering if it could be going bad.
It might be a coil, but coils going bad is relatively rare.
Usually a bad coil will make the car stop running, with little warning, once it warms up.
I would suggest looking at other things, carburetion, a dirty air filter, etc
You could try another coil and see if that helps....pick up one cheap at a wrecking yard or use one from a friends car. Lots of GM cars used the same HEI coil. It should not be too hard to find one.