You have a Cadillac spark plug for each cylinder in the engine on your car. Each one fires independently but they all have to function correctly for the engine to run smoothly. If just one spark plug becomes fouled, then a rough running engine and a decrease in fuel mileage and performance will be experienced. Owners of Cadillacs expect their luxury cars to run smoothly all of the time. To accomplish this, periodic tune-ups should be scheduled over the lifetime of the vehicle. This will include the changing of all spark plugs along with the air and fuel filters. Because of the new ignition systems, most engines no longer have points, condensers, distributor caps and rotors that were also required changing in the past during a tune-up of a Cadillac. The Cadillac spark plugs are designed to supply the combustion chamber with the correct amount of spark at the correct depth in the designed heat range as determined by the engineers. Because of these specifications, the correct type of spark plug must be used in this procedure every time it is carried out. The only adjustment to this auto part is the gap. This is the space between the electrode and the post at the end of the plug. If the gap is not within specified tolerances, then the engine will not be able to operate at optimum performance. When your spark plugs are being replaced, the ignition wires on your Cadillac should also be inspected for wear. A new set of plugs that are not receiving the correct amount of voltage will not fix a rough running engine. All parts of your ignition system must be in proper working order to achieve this goal.