no spark

i have an 86 chevy c10 with 305. have replaced distributer but spark to plugs comes and goes when it wants. what eles could it be?

i have an 86 chevy c10 with 305. have replaced distributer but spark to plugs comes and goes when it wants. what eles could it be?

I'm not up on "modern" ignition systems, but troubleshooting lack of spark used to be a short list:

- Plug wires
- Distributor Cap and Rotor
- Coil
- Distributor (you mentioned you replaced this, but it used to be the last piece to go)

Cracked wires may cause spark to short out to the engine block. It's unlikely, unless the wires are very old, for there to be NO spark at any plug due to a wire issue since wires don't typically go all at once.

A cracked cap or bad rotor contact can also cause spark to "leak" and short to the block or other metal. Either of these could cause all spark to fail at the same time.

Like the cap and rotor, a bad coil can cause complete spark failure. The coil is responsible for generating spark. The other components listed above are responsible for distributing spark to the correct plug at the correct time.

Not sure if that helps or if it is all info you already know, hopefully it's the former.

When it does run, does it run well? If so your timing is probably okay - I'd check #1 the wire and contacts from the coil to the center post on the distributor. If spark comes and goes to ALL spark plugs it sounds more like a coil/coil wire/rotor problem. If it runs poorly (missing, backfiring, etc.) then it is more likely a timing problem, like position of your rotor.