I have just had the most bizarre engine issue I have seen. I have an '05 montero limited which has been fantastic for 124K km until 5 days ago when an engine light came on while on the highway... then the engine died 2 km later and when it was restarted there was a knock that was VERY loud - think hammer on metal. Towed the truck to the dealer and the codes came up as #2 cylinder mis-fire and engine failure.
Turns out that the knock was the spark plug in #2 stripped it's threads in the head and was bouncing up and down from the compression between the head and the spark coil on the cover - and the three inch connector between the plug and coil was missing.

The plug literally looks like it has been beaten with a hammer, the gromet on the bottom of the coil is chewed up and the threads in the head are completely stripped. The tube (boot) going from the coil to the plug is no where to be found. Dealer tech has no idea how this could happen. With the connector not there there is no way the engine could drive without a major mis-fire on that cylinder yet it has been driving great with several long road trips in the last couple of weeks.

Has anyone ever heard anything like this? Does anyone know where to find a schmatic drawing of the Head/valve assembly for the 2005 montero block?

 

I have heard of it happening, but not to that particular engine. I worked on a Mazda6 V6 that had the same exact issue as you described. The poor Mexican dude was stranded and a dealership wanted $1200 to fix it. $40 on a new coil, a new spark plug, some JB Weld, and he was on his way the next morning for a total of about $90.

 

sounds to me like whomever replaced your plugs (im assuming with 125k on it youve replaced them) did NOT torque them properly.

 

I have seen this happen with factory torqued plugs. Sometimes the little thread sleeve can pop right off.

 

Which sleeve? Is there a sleeve in the head?
Now I am being told that the connector wasn't there and basically being asked why I took it out... nice. They say it was not in there so it must have been removed but that without it the truck would have been misfiring all the time which it wasn't for the last 4000 km. I don't get it. There is no where that connecting tube could have gone unless it fell off during removal and there is no way the truck could operate propoerly without it for more than a few feet of driving let alone 4000 km!!

 

They have kits wher you drill out and tap the plug hole and then install an insert w/ threads. Older ford trucks are known for doing the same thing.

 

The car I worked on had that coil+the tube just get obliterated to the point where I couldn't find 90% of it. Any f-ing mechanic should know that.

 

who ever did your tune up was probably knocking down a few brewskies at the same time!! a new head will do the trick. check the top of that piston and the cylinder wall for damage