Ford 4000 spark plug wires shooting off

[banc123]

I had a thread the last few weeks about an ignition issue that ended up being grounded points. Got that fixed, thanks again for the help.

As part of working through the other issue, I changed the coil, rotor, plugs, points and condenser.

I ran it for the first time today with a load (bush hoging medium tall grass).

About 10 min into it, it started acting like it was running out of gas, but I had just put 5 gal in it.

I opened the hood and found plug wire 3 and 1 were not connected. Plugged them back in and it kicked back up. 5 min later plug 3 popped out again. That repeated every 2-3 min. With hood open and battery tray slid out, I watched the plug wire shoot off the plug like a sling shot.

Only thing I could think of is the new plugs werent seating in the wire housing. I trimmed the bottom of the rubber socket cap (part the seats in the hole) maybe 1/8 and pushed it on hard. Ran it probably an hour and had no more problems.

Anyone ever see plug wires shoot off a plug ? Had to have been it wasnt sating and its running a hotter spark with all the new parts.

 

[Reb954]

It sounds like the new plugs aren't seated properly. Gas is coming out between the plug and the head. Remove plug, clean and reseat.

 

[banc123]

Had about 1/16” turn to fully tighten, ran it for a few hours this morning no issues. Guess in the process of not wanting to overtighten they didn’t get seated.

 

[Mace Canute]

I've seen this happen previously when a plug and wire change was done and the plugs were tightened properly. What I believe happened was one of two things...(A) there was enough clearance between the center electrode and the ceramic insulator to allow compression gases to migrate through into the boot and when the pressure was greater than what the boot could hold, it popped off. Once ran enough, combustion residue finally plugged the gap and they stayed on OR (B) the heat from running caused the boots themselves to "outgas" and the resultant pressure caused them to pop off. Once ran enough, the outgassing lessened a great deal and they stayed on.

I have a hard time believing enough combustion gasses can make it by loose sparkplug threads to blow the boots off considering how tight they do fit and the fact that there's quite a bit of distance between the boot and the head and the metal portion of the sparkplug shields the boot to a great degree.

 

[RickB]

I have a harder time believing combustion gasses travel through a spark plug. I have seen this problem a few times and retorquing the spark plugs has cured it every time. There is zero clearance between boots on 3 cylinder Ford OEM plug wires and they certainly seal tight enough to blow off if combustion pressure gets into the plug bore in the head from any route.