The funny thing about spark plugs

[RAT]

I hadn't seen this phenomenon for a very long time, so I had forgotten this can happen. I replaced my spark plugs (2002 TJ 4.0) in 2008, at about 43,000 miles. Didn't really need to but figured what the hay. I started getting engine codes a few weeks ago; cylinder #4&6 misfire. I thought is was a issue with the crankshaft sensor (another story) but couldn't isolate it to that. Pulled the plugs and found the Outer electrode on each spark plug has softened and won't keep the gap. The gap measured 45-50 on all 6 plugs. I set the gap back to 33-38 but the electrodes have softened up so much they can't hold the gap. Crazy stuff man. I had this happen in a small block Chevy race engine before back in the 70's. Those plugs were AC Delco. These now are Motorcraft. I know, Ford plugs in a Chrysler. Oh well... Just though this would be good info in case anyone starts throwing the same codes. Check the gaps first.

[inVERt'D]

Everyone knows electrodes erode over time, but getting softer? Maybe they're too hot?

I'd had a Cyl 2 misfire in my Saab for awhile, and finally got around to pulling the plugs before a SMOG test. All four were gapped at around .060" , and this on not-very-powerful ignition system. Re-gapped them to .028 (on the wide side for this vehicle). No more code, passed SMOG, runs smoother, has more power, and uses less gas. IIRC, the plugs are NGK. They weren't eroded, but I can't figure out how they all ended up being around .060".

[bails85]

why not just put new plugs in it. they arent very expensive and you can do it in 15 min.

[inVERt'D]

I'm not going to spend my money on spark plugs, I'm waiting for a stimulus package from Daddy-O'bama.

[Jeeperator]

Get this a long time ago with my modded kawasaki jet ski I had the head milled for more compression. I also had ngk plugs and man that thing ran like a bat out of hell but after a long hard run it would start missfiring. Figured out the center electrode would some how get pushed up into the porcelin tip making the gap way to big. The engine was apparently detonating and the extreme pressure would shove the electrode tip into the porcelin. I just kept closing the gap to make it back. Weird found out later the head was milled wrong. Another thing is dont use Bosch platinum tip spark plug they will leave you stranded. The tiny platinum electrode wears into the porcelin and the gap increases without you knowing it.