Hello everyone i am having a problem with my faters explorer and cannot figure out what is happening. The truck is a 1999 Ford Explorer witht eh 4.0L engine. We have replaced the spark plugs with ford plugs and we are having a problem with one of the plugs. The porceline is tottaly gone and the truck starts to missfire. We have replaced the spark plug 4 times now and it happens again. Not sure what the problem is but it is on the same cylinder every time. Any suggestions on what i can do and why this is happening? Thanks and much appreciated.
Brian

 

So, the porcelain insulator on the bottom of the plug, along with the center and ground electrodes are gone?

Or is it the top of the plug?

If it's the part that screws into the motor, you may have a teardown in your future, as something is hitting the plug.

Are you certain you bought the right plugs? Not sure, but there are two models, and variations nearly every year. If your plugs are for the wrong model, they could be the wrong reach, and hit a valve or piston.

The biggest difference is between the OHV and the OHC models.

Which do you have, and what plug number are you using?

 

Thanks you for your input. It is just the porcelin part missing at the end(end that is screwed into the head). the center and ground electrodes are fine. I dont have the plug number handy right now but i will post it when i can get it.

 

4 times the lower porcelain breaks....Something must be hitting that plug. Any signs of damage, nicks etc? The cylinder must still have all that broken stuff inside too....not good.

Which engine do you have, ohc or ohv/pushrod?

 

Any chance you could post a photo of one of the plugs to make sure we are all on the same track? You would need to upload the photo to a photo sharing service, then provide a link to it here.

-Rod

 

Check for coolant leakage into cylinder, causes detonation and destroys the plug ceramic as you describe.

Head gasket, intake manifold gasket, cracked head.. Coolant system pressure test, hot and cold, cylinder leak-down test (look and listen for air in rad)

 

Hey thanks all i will try to get photos in the next couple days. As for the engine i a mnot sure i will have to ask my father. Also he brought it to a family freidn today who is a tech and he thought it may be a haed gasket and the coolant getting into the cylinder. i will keep you posted and thanks very much for the info it is much appreciated