My truck is the one in my sig. Last night my truck started to misfire so I pulled over to the side of the road to see what I could see. The drivers side was fine but the passenger side had blue sparks coming from the first two wires down by the boots. They were flashing at a steady rate so I think it's happening with every firing cycle. I also saw an occasional flash from one of the rear plugs although I couldn't see which plug it was coming from as the EGR plumbing was in the way.

Today I pulled the first two plug wires and plugs. Everything looks fine. The plugs have no cracks in them and the wires and boots are solid. I can't see anywhere where the spark could jump from. Does anyone have any ideas where I could look next?

 

High voltage can and will escape with the smallest cracks in the plug wires, even invisible to the human eye. Replace all of the plug wires. Also suggest to do the cap/rotor and plugs if they are the same age.

 

You're looking in the right place.

How many miles do you have on the plugs? On the wires?

Plugs wear out over time. As they wear the firing voltage increases. Once the plug's firing voltage gets high enough the spark will take an easier path to ground, where the firing voltage isn't as high.

Plug wires also wear. They get to the point they won't keep the spark contained within the desired path through the firing end and will allow the spark to go to ground wherever it can.

For now, try putting a pea-sized blob of dielectric grease in the end of the plug boot when you connect it to the plug. That should reduce if not eliminate the sparking off the end of the plug boots. And budget for new plugs and plug wires in the near future.

 

Thank you for the replies. My plugs, rotor and distributor cap are almost new, 10,000 Kms or so on Motorcraft parts and NGK Iridium plugs. The wires are NGK Silicone and have less than 1000 Kms on them. That's why I'm confused about where the spark is coming from.

Broke Vet, I will give the dielectric grease a try and fire my truck up tonight to see if I can see any more sparks.

 

Yea sounds like boots are damaged.

Does it have the factory heat shields in place for the plug wires yet or are they gone?

If they are gone, someone removed them or and or rusted away over time you're gonna need plug wires for headers, they'll take the heat the factory wires won't.

Also make sure your base timing is correct, for example late timing if late enough can and will cause the manifolds glow red hot under load (when you wouldn't see it) if the shields are gone making a bad condition worse burning up the wires at the plug end.

 

Danr1, yes it has the heat shields in place. I had the mechanic who replaced the exhaust manifolds install new ones last year.

I spent about 10 minutes under the hood tonight while it was totally dark out. I discovered that cyl's#1,2,3 and 6 are misfiring. 1 and 2 are giving a constant spark even though I put dielectric grease on them today, while 3 and 6 only misfire once in a while. I also noted a blue spark once from the coil area but couldn't pin point it as it didn't happen enough times so I could lock on with my eyes and then turn on my light.

It seems like my wires are defective? Yes, no? They are virtually new and they are NGK Silicone wires so they shouldn't be? All of the plug sparks are coming from the area by the plug. By that I mean it looks like they may be coming from the end of the boot but it is very hard to tell. All I can say for sure is the spark is from the area where the boot ends and the porcelain of the spark plug is exposed before the metal body of the plug begins.

How far down the spark plug are the boots supposed to go? I have about 1/4" of exposed porcelain, maybe a bit less. Is that about right?

 

Based on what you've said then I'd swap out the plugs for set of Motorcraft's, see if them Iridium plugs are to high resistance causing the juice to simply find easier path to follow rather than all if it going through them.

Simple test know if it made a difference or not first time you watch it in the dark.

 

From what I've been able to determine iridium plugs don't have any higher resistance than standard copper plugs. Or, if they do, then their resistance is so close to standard copper plugs that it is negligible. The benefit of them is supposed to be easier starting, smoother running and better performance and/or gas mileage.

My truck was running perfectly until last night and then BAM, it started to misfire. I think I'm going to load up the dielectric grease tomorrow and see what happens. I didn't overdo it on the two plugs I tried it on today. Tomorrow they're gonna get it!!

 

"How far down the spark plug are the boots supposed to go? I have about 1/4" of exposed porcelain, maybe a bit less. Is that about right?"

there's no answer to this question in terms of inches or millimetres; you need to feel the spark plug lead seat itself onto the plug ... i like to squeeze the end of the spark plug boot between my thumb and forefinger, then push/wiggle it into place until you feel that connection being positively made. not always possible to because of the awkward placement of some plugs, but the same thing can be accomplished with a suitable pair of pliers in tight spots. squeezing the boot against the wire reduces the possibility of pushing the boot down but leaving the lead behind, resulting in no actual contact between plug and wire. sounds like this may be what happened in your case ?

 

No time to look at my truck today so I'll have to work on it tomorrow

 

Yep, clean off all of your block grounds and the terminals for the block grounds, as well as the negative battery post clamp......and obviously make sure they're all snugged down as well.
A wire brush in a drill or a dremel tool will clean 'em up nicely.
Inspect the negative ground cable thoroughly as there may be "hidden corrosion" under the sheathing too.
You may have had a grounding bolt/nut loosen up somewhere under the hood too......check all possible grounds.

A poor block ground going back to the battery will be resistive and cause the "light show" you're having.

Been there, chased it, then fixed that one.

Bob