2003 GMC C1500 Engine lilte on and engine missing

Hello,

Just saw your web site and up a membership, so this is my first time to use it.

Yesterday, my engine light came on and started blinking, then the engine started running rough, and after a few minutes, the engine light stayed on (no blinking). The owner's manual said it was either the engine missing cauisng an emissions issue.

Last night I installed new spark plugs. No change, stilll ran rough and light was on. This morning I took it by my neighbor's shop and discussed the situation. He suggested I replace the rotor and distributor cap. I just did this (using DELCO parts). Still no change, engine light is on solid when the truck is started, I drive it and the engine light blinks a few times then goes solid. It sound and feels like a cylinder is not firing.

Now I am going to disconnect one plug wire at at time, start the engine and see if the miss gets worse and to see If I have a bad plug wire.

In the back of my mind, I am thiinking O2 sensor.

What do you advise.