[HotZ28]

Bad spark plug wires are a common cause of misfire, with or without codes. The wires may be leaking current to ground or other wires, shorting the spark before it can reach the plug. Also, internal resistance may be increased, raising the required firing voltage to the point where the engine may misfire. You said the wires are good, however, did you check resistance of the wires to see if they are within specifications? You may also want to change one coil/wire out with another, to see if the “weak spark” moves with the coil and or wires. Another quick test, would be to check the suspect coil/wires in the dark to see if you have visible signs of arcing. It helps to spray a mist of water in that area, prior to checking.

Low coil output can also be caused by a faulty ignition module or a faulty coil driver circuit inside the PCM. A lot of coils are replaced unnecessarily because problems like these are overlooked or misdiagnosed.