1994 Ford 7.5 liter. #3 plug wire on passenger side has blown through the boot at the plug three times in the last 2000 miles. What is causing this?
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Are you changing the boot or the entire wire when this happens? If changing the wire, are you utilizing the same type of wire when you replace? Also, have you checked the spark plug to see if there are any issues with it? Also, I'm assuming by "blown through the boot" you mean that electricity has found a way to ground through the boot?– Pᴀᴜʟsᴛᴇʀ2 ♦Aug 4, 2014 at 21:42
2 Answers
I have seen many a Ford engine burn thru the boot on plug wires and coil-pack boots. After driving like this a while they appear to have exploded or melted out. If it is a coil wire, replace the wire and the spark plug (all of them if they are due!). If it is a coil-on-plug style ignition, Ford recommends, and so do I, to replace the coil and boot and plug (again, all plugs if they are due) to properly correct the issue. Having fired thru the boot to the block adds stress to coil packs that will make them fail prematurely. I highly recommend using Ford/Motorcraft parts for the ignition system. Aftermarket parts have to high a failure rate for me! It's cheaper to do it right once than many times the cheap way. Also, clean very thoroughly the plug well for any oil or debris. This can cause carbon fouling making it fail repeatedly.
~Jonathan
Na, can't happen. It might be TUGGED out by something (possibly snagging on something, then engine torque pulling it out), but it CANNOT be blown out of the boot. There's nothing there to exert pressure - only the spark plug itself, the wire, and the boot.
There's the slightest, most remote possibility that the spark plug's inner electrode has somehow burned all the way through from end to end, and compression is blowing back through the now-hollow spark plug, but that possibility's so remote as to be VIRTUALLY impossible. One in a hundred trillion.