Cylinder 3 misfiring... can anyone help????

[03gtmustang]

My friends check engine light came on the other day so I ran the codes with my superchip and the code P0303 came up which is Fault Cylinder D-Misfire on cylinder 3. Can anyone tell me how this can happen? What could be causing the problem and what needs to be replaced. Its a 97 or 98 GT with a little over 100,000 miles and is all stock.

 

[5.0's 4 ever]

Could be a lot of things, a bad spark plug, valve cover leaking oil down in the spark plug hole, or a bad spark plug wire.
With a 100K miles on the car it is due for tune-up, I would replace the spark plugs and wires, also check to see if the valve cover gaskets are leaking.

 

[03gtmustang]

Could be a lot of things, a bad spark plug, valve cover leaking oil down in the spark plug hole, or a bad spark plug wire.
With a 100K miles on the car it is due for tune-up, I would replace the spark plugs and wires, also check to see if the valve cover gaskets are leaking.

So replace the spark plugs first? Any recommendations on spark plugs?

 

[5.0's 4 ever]

Pretty much up to opinion, motorcraft, NGK, autolite are all good plugs.
Spark plugs would be the cheapest and easiest thing to replace first, but I would not be suprised if its a bad wire.

 

[03gtmustang]

Pretty much up to opinion, motorcraft, NGK, autolite are all good plugs.
Spark plugs would be the cheapest and easiest thing to replace first, but I would not be suprised if its a bad wire.

I think the spark plugs were replaced 15-20k miles ago, but the wires have never been replaced.

 

[COramprat]

I think the spark plugs were replaced 15-20k miles ago, but the wires have never been replaced.

Change em...go with 9mm wires if you can find them local.