I understand why spark plugs need to be changed on a vehicle with a distributor cap.
In a distributor cap system, voltage is held pretty much at a constant, and the spark fires when the rotor gets close enough to the pin that the breakdown voltage falls below the coil voltage.
Carbon deposits act like resistors and can alter the breakdown voltage. A fouled spark plug, or one that has enough wear to alter the gap distance, can cause timing problems.
But on a coil pack driven car, like the Corolla, firing happens by computer and is completely independent of spark gap distance. (Thus the admonition not to adjust the gap distance.) So if this is the case, it seems to me that either the spark plug is firing and igniting the fuel, or it isn't.
If it isn't you'll know because you'll get misfires. If it is, then it seems a total waste to replace the plug.
Is there any reason to replace an functioning plug that I'm missing? Because it seems to me that regular replacement of spark plugs in a coil pack car is just wasting $$$....
In a distributor cap system, voltage is held pretty much at a constant, and the spark fires when the rotor gets close enough to the pin that the breakdown voltage falls below the coil voltage.
Carbon deposits act like resistors and can alter the breakdown voltage. A fouled spark plug, or one that has enough wear to alter the gap distance, can cause timing problems.
But on a coil pack driven car, like the Corolla, firing happens by computer and is completely independent of spark gap distance. (Thus the admonition not to adjust the gap distance.) So if this is the case, it seems to me that either the spark plug is firing and igniting the fuel, or it isn't.
If it isn't you'll know because you'll get misfires. If it is, then it seems a total waste to replace the plug.
Is there any reason to replace an functioning plug that I'm missing? Because it seems to me that regular replacement of spark plugs in a coil pack car is just wasting $$$....