Originally Posted by rainbonh
I seem to be replacing a plug every 3 or 4 months or so. #5 twice and #3 another time. The enamel has cracked around the electrode in two cases and the electrode itself kind of disintegrated on another . I was told early on that I needed a valve job for $1500. Went for a second opinion. Diagnostics showed it to be #5 plug. Cost $105. 3 or 4 months later and two times after that same issue. 2000 ranger starts bucking again. Has 13000 mile on her. Driving me crazy. Good truck other wise.
You should have started your own thread for this.
First, you can only use Motorcraft or Autolite spark plugs in a 4.0l OHV engine, it will "eat" all other brands.
2000 Ranger has the 4.0l OHV engine, 2001 got the 4.0l SOHC.
Ceramic is pretty sturdy stuff so doesn't crack easily, but what can crack it is heat and/or shock waves.
If a cylinder is running Lean it will heat up, this can also lead to pinging/knocking.
Pinging is a shock wave, it will damage pistons, valves and spark plugs.
Lean on one cylinder often won't show up on O2 sensor.
You could just have a couple of dirty injectors, run a can of Seafoam in the gas tank, see if things get better; I put in a can every year, seems to cut down on the odd ball misfires at idle.
Make sure EGR system is working, EGR cools cylinders when engine is under load, accelerating.
Check those spark plugs every few weeks or more often, take pictures of the tips each time, see if you can pin point when they start to fail.
Valve job is done when valve seats are leaking "air/exhaust" so you get low compression, it would have nothing to do with spark plug issue you are seeing.
If you are burning a little oil that is valve guide seals, under the valve covers, they can be changed without removing heads.