Constant #4 sparkplug failure.

[mkinttrim]

My son has a 99 ranger 4.0 with about 140000 miles. About every 2 months the check engine light comes on and the code always comes up lean condition. Almost everytime this happens we pull the plugs and the #4 plug has failed, no spark at all, one time the electrode was missing, another time it was cracked, and the latest time it just plain stopped working. Plug wires are good. Have been usuing motorcraft plugs but this time we tried the bosch, will see what happens. When the plug was removed I told my son to start the engine without the plug in the head to possibly blow out a chunk of carbon or crud. Don't know if that will help but probably won't hurt anything. Anyone else have any ideas?

 

[289-tiger-]

My son has a 99 ranger 4.0 with about 140000 miles. About every 2 months the check engine light comes on and the code always comes up lean condition. Almost everytime this happens we pull the plugs and the #4 plug has failed, no spark at all, one time the electrode was missing, another time it was cracked, and the latest time it just plain stopped working. Plug wires are good. Have been usuing motorcraft plugs but this time we tried the bosch, will see what happens. When the plug was removed I told my son to start the engine without the plug in the head to possibly blow out a chunk of carbon or crud. Don't know if that will help but probably won't hurt anything. Anyone else have any ideas?

Good evening,

Have you checked compression on the jug?

Good luck

 

[srteach]

Broken or missing electrode indicates pre-ignition. This happens when the engine is run lean and tries to advance timing. You need to find the cause for that.
When i had the problem, an O2 sensor was bad. Replaced all three and the problem went away. Not saying it is your issue, just my experience.

 

[Big Jim M]

One plug over and over indicates to me that you have a leak in the intake manifold very near that one cylinder.. If you keep running it thataway you will blow up a piston .. POSSIBLY could be an exhaust manifold leak also.
Check it out.
Big JIm

 

[94STXRanger]

Or a burnt valve?

 

[Big Jim M]

A burnt valve?

Or a burnt valve?

The burnt valve would be the result of the vac leak and not the cause of the plug problem..
Big JIm

 

[bighoss94ranger]

The 90 to 99 rangers had a bad habit of the intake manifold bolts coming loose. Sometimes you could just retorque them, other times you had to replace the intake gasket paying special attention to tightening sequence and torque spec. Hope this helps, Hoss.

 

[Hotrodlincoln]

Agreed, detonation is damaging the plug, and if it hasn't already, will eventually cause piston or rod damage if allowed to continue. You need to find out why #4 is leaning out and get it fixed asap.