Hello so I bought this car at 107k miles. Carfax indicated spark plugs changed at 60,000 miles at a ford dealership (plugs and wires). I decided to change the plugs and wires since it was hitting that time. Anyways I pull the old spark plugs out and they are motorcrafts SP486 (stock) but they are gapped at .048. Everything seemed fine on them just worn out (white tips). I replaced with the same exact plugs motorcraft SP486 but I set the gap to .054 because that is what spec indicated. Drove the car and it accelerates fine but it is missing and/or dropping out at idle a bit. Definitely not normal at all.

My question is why were my gaps set at .048 and should I take the new plugs and gap them at that to make the car run fine again? I pulled the plugs back out and they have blue /chrome/shiny colored on them that could be wiped off. Fuel/Oil?


Possible variables: I tried changing passenger pre-cat O2 sensor and failed at getting it off earlier that day. I disconnected it and reconnected it fine. Also spark plug wires have not been changed yet (getting them in mail today)

98 mustang 3.8L 108,360 miles

 

Gapping plugs changes how "hard" the plugs fire. The wider the gap, the harder they fire. Meaning you get more arching from the cathode to the metal meaning more cumbustion. Shortening the gap is used on high powered, often FI motors, to help prevent pinging under certain loads.

You gapped your plugs right, odds are you didn't made a good connection with one or two of them with the wires causing the misfire. The blue color is gas caused from the plugs not firing.

The other possibilities are that one or more of the wires are bad and when you unplugged them one ore more of them lost contact on the inside of the jacket. Spark plug wires can be prone to dry rotting over time and this along with other things is what happens when they dry rot.

You should always change your plugs and wires at the same time to prevent this very issue from happening.

 

thanks for the detailed reply the new wires did do the trick!

 

What brand wires did you use? Im STILL letting my tune up go for far longer than I wish due to money problems but I have my eye on some nice wires.