Spark Plugs Self Destructing

wkeller · #1 (**permalink**) 04-17-2008, 09:47 PM

My neice bought a 2000 Explorer Sport with a 4.0 back in November. Soon afterwards it developed a misfire and the CEL came on. I put on a new set of wires and a new set of plugs. I noticed when I replaced the plugs that the #3 plug was missing the ceramic near the electrode. I figured it was just a cheap Bosch plug and didn't give it much thought. The vehicle ran great.

Recently the misfire came back and the CEL came back on. When I pulled the plugs #3 had a cracked ceramic around the electrode, #4 was wet with fuel and not firing at all, and #6 was completely missing the ceramic around the electrode.

I replaced the plugs again, replaced the coil pack and cleaned the MAF sensor and it's running great again.

My question is, what would cause the ceramic to disintigrate on the plugs? There didn't seem to be any pinging or detonation. I replaced the coil pack because I thought maybe it was erratic, loading up on fuel and then causing a big bang and then destroying the plug. Are my thoughts way off? I want to make sure this is fixed so that it doesn't tear up anything else.

aquanaut20 · #2 (**permalink**) 04-20-2008, 07:41 PM

Over torquing the plug and detonation are the most likely causes. Second would be wrong heat range. Or......!!
Tried Bosch+4 in mine and same thing happened to 2 sets <5k each set, sent them back to Bosch lab, they said "plugs good, must be engine".

Installed NGK-P with 85k on them, +20k since reinstall, still firing good.

wkeller · #3 (**permalink**) 04-21-2008, 04:07 PM

Over torquing is a possibility. It was cold, dark and raining and I had just gotten home from work when I started working on it and I was basically working with a flash light when I put them in.

To make matters worse the only tool that I had that would get the old ones out was a 1/2 drive ratchet with a ratcheting head. Since I was in a hurry to get in out of the cold, I use the same tool to put the new ones back in. Maybe the 1/2 drive ratchet was a little much.

TheHandyman · #4 (**permalink**) 05-09-2008, 11:20 AM

I think I read of a Bosch issue with the 4.0 Aerostar too. They recommended to use Motorcraft or Autolite (was owned by Ford), which is what I recommend too.