Hello to all, I have a 98 F150 Lariat 4x4 with 4.6. I'm the second owner of this truck and have always kept up on everything. Last summer I changed the plugs, wires and coil packs all with Motorcraft. About 10,000 miles later the wires started to short out, I pulled all the plugs to check the gap, inspected the wires and coils, everything looked ok. I replaced the Motorcraft wires with NGK and now about 3,000-5,000 miles later 3 wires are starting to short out again. Any advice or suggestions would be a big help. Thanks

 

What exactly do you mean by "shorting out"?

 

The insulation on the wires appear to have broken down, there is no burn marks or cuts in the wires, but when I done the water mist test I could see different spots along the wire arcing... hope that helps, thanks for the reply

 

Do you have a misfire.... or codes for misfire? I've never heard of this test you're talking about. I usually perform that arc test by watching it run at night. I've never applied water to anything on the ignition system.... it doesn't like water.

 

No misfires or dash lights coming on.. but at idle the exhaust has a different tone to it than normal. That's pretty much what I done was wait till night and mist just the wire insulation and you could see the arcing. I'm so stumped on what this could be.

 

I would not use anything but Motorcraft or Denso wires on your truck, for starters. The modular motors are very particular about wires and plugs.

How are they routed? Do you have them separated well? Plug wires don't last as long when you bunch them up together, and arcing does occur.

 

I hear what your saying about using straight motorcraft on these motors, and I agree. But after the first set only lasted about 10,000 miles I was a little hesitant to buy again. I have them routed as close to factory as I could get them. Don't know if the pics help any.

 

 

@white89gt if wires are spaced out properly, is there anything else that could be causing the wires to go bad so quickly? Appreciate all your input so far brother.

 

A few things can cause it. Running too rich, low compression, leaking head gasket, bad plugs, bad wires, bad coils. One of those things is not letting the plugs use the full spark, or is allowing a quicker path to ground.