Changing spark plugs requires more than just the ability to pull each one out and put a new one in the empty space. It is essential that they are rewired correctly before the engine is started. The three critical components to ensuring that the spark plugs have been properly rewired are firing order, cylinder numbering and distributor rotation direction. Understanding and incorporating these key components will make the process easy to comprehend and follow.
Purchase a repair manual for your specific make and model. Repair manuals can be found online, at local auto part stores or by visiting the car dealership service centre.
Determine which way the distributor rotor turns. The rotor is located underneath the distributor cap. It spins either clockwise or counterclockwise and is referred to as distributor rotation. Remove the distributor cap, crank the engine and make note of the distributor rotation direction. Reconnect the distributor cap.
Look in the repair manual to locate the distributor's number one firing terminal. Many distributor caps come manufactured with the number one terminal already marked. An alternative method is to point the distributor's rotor to the number one terminal by manually turning the engine until the crankshaft and camshaft timing marks line up. Look in the manual for specific instruction on using this method.
Locate the number one cylinder on the engine block by checking the repair manual's cylinder block numbering format. The cylinders are numbered and oriented differently depending on the make of the vehicle. Connect a spark plug wire between the number one cylinder and the distributor's number one terminal.
Recall whether your rotor moves clockwise or counterclockwise and connect remaining spark plug wires, one at a time, following the firing order located in the manual. The firing order starts at the distributor's number one terminal and continues in clockwise or counterclockwise fashion until reaching the number one terminal again. If the manual gives the firing order as 1, 3, 2, 4 and the rotor moves clockwise, connect cylinder three to the distributor terminal immediately clockwise of the number one terminal. Connect cylinder two to the distributor terminal immediately clockwise to the number three terminal and connect cylinder four to the distributor terminal immediately clockwise of the number two terminal.
Compare the spark plug wires to the manual's firing order and make sure each wire is attached to the correct distributor terminal.
If engine backfires or runs rough, turn off engine and verify the wires are connected correctly.