2003 mazda protege lx spark plug problem need help

I have been driving this as my everyday for the last 8 months but ive noticed the 4th spark plug shorten even tho i have e3 dimond sparks can anyone figure out why i mean the alternator is starting to go out i have the replacement but im sure this is not the issue as it has been happening since i got the car the old sparks were in i sware from the factory i replaced them with acdelco silver and a month later the fourth one was almost touching making it not spark help would be greatly appreciated. Thanks.

I suppose you're talking about the ground strap that wraps around the bottom of the plug? If so, it's usually a foreign object in the combustion chamber or the piston touching it. I've seen a few cases of extreme detonation cause something similar, but those instances are few and far between. Have you done a compression test or used a borescope to check inside the combustion chamber? You can get borescopes really cheap on eBay now and you can rent a compression tester from AutoZone.