The V6 5VZ-FE engines are equipped with what is called the Toyota Direct Ignition (TDI). This system improves the timing accuracy and enhances the overall reliability of the ignition system. The TDI uses a two-cylinder simultaneous (waste spark) ignition system which fires two cylinders at the same time with one coil.
In a waste spark system, one spark plug is attached to each end of the secondary coil winding. This circuit arrangement causes one of the plugs in each cylinder pair to fire in a forward direction, and the other to fire in a reverse direction. The cylinder on the compression stroke is defined as the "event'' cylinder, while the cylinder in the exhaust stroke is called the "waste'' cylinder. The coils are positioned over one bank of the plugs. This arrangement has eliminated half of the normal required plug wires.