Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance Spark Plug Questions (Arcing)

In the past 6 months I have twice changed the spark plug in the #3 cylinder of my 96GL. Both times the car would show symptoms of a misfire for quite a while (2 months) before it would throw a CEL. Each time the #3 plug showed visible signs of arcing and upon replacement the car drives fine. I guess my question is what could cause this to happen? The wires are off of my SVT and only have about 50K Km on them. The first plug to fail was a six month old Autolite and the second was a used Motorcraft again off of my SVT with about 50K Km on it. When I changed the plug again this weekend I decided to use dielectric grease on the plug insulator and in the plug boot (I did this for all 6) in hopes of solving the problem. Is there a chance that the lack of dielectric grease caused the issue or is the #3 wire gone bad? I should also mention that the reason I changed the factory original wires for my used SVT wires was in an attempt to fix the misfire problem when it first started to happen earlier this year, leading me to believe that the wires are fine. Have a look at the pics of the plugs to see the arcing. Also, is the change in color (tanning) of the insulator outside the cylinder a cause for concern?

That exactly happened to me, #2 center rear cylinder, twice. It's good to use silicone dielectric grease in the boot, make sure the sparkplug socket wrench is clean and your hands too. I cleaned out the boot inside, greased, new plug, good so far, we will see after winter. I think dirt on the plug insulator, dampness cause the arcing, it's an easier path than sparking inside the engine! The grease should seal it out. I actually gapped the plugs a little tighter than specified .050 instead of .052. They will spark easier, I think, and the voltage will stay inside the plug! I get the same exact tan rust/heat stain.

The tan color is often from oil in the spark plug well. Oil in the well can also be the cause of carbon tracking on the upper part of the plug and where it mates to the plug wire boot.

If you do have oil in the plug well, it is usually from the a valve cover gasket leaking.

Get NEW wires, period. The factory wires always go bad and cause misfires, anywhere from 30K+ miles on. THat would be right around your 55000 Km that you are reporting. Yes, there are some sets that last significantly longer but most don't and if you are having ignition problems it is just best to get a new set.

Thanks for the info guys, maybe I'll buy my wife a set of wires for Christmas .

Almost all brands seem to fail IMO. The Ford Racing wires are only $45 so why not get something a little better than stock?

I am a proponent for the FMS wires too.

BTW Todd - the common misunderstanding is that the overall diamter of the wire is proportinal to the resistance - this is WRONG. The conduit is in the very center and is MAYBe 1mm wide at most. the rest of it is just RFI suppressant. So 10mm or 15mm wires won't have any lower resistance than the 8mm wires. That is not to say all wires are the same as the quality of the actual conducting center wire affects the resistance AND some "big" wires have crap insulation which allows arcing and RFI.

That is not caused buy arcing, it is caused buy blowbuy from the cylder throu the spark plug.
sorry for the spelling