What causes this to happen to a distributor cap?
 

Been having hard start issues on both cold and hot engine.car never ran rough, just hard start, idle is really smooth. Took off distributor cap and saw this. Cap was replaced 6 months ago, plugs maybe 1 month ago, rotor 6 months ago, wires 3 months ago maybe. (I replace parts on my car often for peace of mind and because I have warranty.)

engine ground strap?Coil,inferior materials in cap.

Ismalley, is there an O-ring on the distributor base? It looks like moisture is getting inside the distributor. Are the distributor cap and rotor Bosch brand? How old is the coil?

Hard start issue could be due to leaking fuel injectors that bleed off fuel when the engine is turned off.

O ring was in place. Everything was Bosch brand except for Champion plugs (though I highly doubt the brand would have anything to do with this), all fuel components from the fuel pumps to the fuel injectors are new (less than 1 month old). Plugs look brand new, they are only slightly brown and have zero carbon or any other type of build up. Could a faulty ignition coil or ezl cause this? I replaced the cap yesterday as well as my alternator (again, not throwing parts, just replacing because I have these on hand and get them replaced free), but I'm worried that there may be another issue causing it and don't want to fry this one. I do have an extra ezl and ignition coil on hand too, but as I've said the car runs incredibly smooth with no hiccups in idle and I'm not sure if a hard start issue would be failing symptoms of the coil or ezl. I think I read somewhere that when those components fail then it is total failure and the car won't even start or run. I could be wrong though.

I run extra ground straps on both my cars.One from negative terminal to block,and one from body to block.

wrong gap on plugs and/or too much resistance in the wires. my clients don't get bosch wires or champion plugs. beru or karlyn wires and oe bosch plugs when available. if not, ngk. good luck, chuck.

Is there any oily residue under the cap? If there is it may be coming from the camshaft seal.
Is the large oring seal for the cap still soft or hard as a rock and cracked? I had to replace mine many years ago.
Are those Champions resistor plugs?
How bad is the rotor?

Rotor isn't bad at all except where the center part of the distributor was fried. The Champion plugs are non-resistor with solid copper core. O ring on distributor was brand new and still soft. Cam shaft seal was replaced the same time I did distributor 2/21/16, so less than 6 months.

The spring loaded carbon button in the center of the dist cap is burned away.

Was the cap fully seated?

Is the bolt pattern such that it can be rotated 180? If so there is usually a tab that prevents the cap from seating when 180 out and perhaps the cap was pulled away from the rotor allowing the button to lose contact with the rotor.

The stuff on the terminals looks like grease, did you add something to them?

Cap can't be rotated. But the grease you are seeing is dielectric grease from a dirty rag I used to try to clean up the cap. I didn't want to use any chemicals or cleaners inside the cap, but after seeing the amount of damage it wouldn't have made a difference what I used to clean it with because it was toast anyways, just thought that I could've salvaged it if it was just dirty

Very hot spark...think outside the cap. Coil as has been mentioned. Is your alternator regulator ok? Have you installed solid core wires? Have you installed some sort of wire organizer?

I had the same issue, although my caps were burning every year. Swapped in a good used ignition coil and things went back to the normal 3-5 year interval

Brand new 120amp alternator installed yesterday, before then alternator was replaced in 2012, but vr was swapped out every year. Actually, with my spark plugs, I am running non-resistor Champion plugs that I converted to non resistor plugs by removing the resistor and installed a solid copper core, but I've done this for a while and never an issue. I will try the ignition coil first

The burn-away at the center contact of the dist. cap may be a clue.
Although there exists deliberate clearance between the rotor tip and the individual cylinder terminals in the cap (and hence an arc), the center, carbon, contact is spring loaded against the rotor. If the carbon or the spring were missing, or the spring were broken, the resulting arcs, in an area not designed for an arc, would quickly cause the observed damage.

As far as plugs I use Champion too.I used bosch,denso,NGKs bosch 3's and denso 5061's ,and they would carbon up in less than 6000 miles.Now running Champs for over a year.