IGNITION TIMING

Man, did that feel like 40,000 Volts!!!

IGNITION TIMING FACTORS n Ignition timing is how early or late spark plugs fire in relation to position of engine pistons n Ignition timing must vary with engine speed, load and temperature n Must be advanced at times and retarded at other times

METHODS OF IGNITION TIMING n DISTRIBUTOR CENTRIFUGAL ADVANCE n DISTRIBUTOR VACUUM ADVANCE n ELECTRONIC (COMPUTER) ADVANCE

IGNITION TIMING COMPENSATES FOR BURN TIME

CENTRIFUGAL ADVANCE n VARIES IN DIRECT RELATION TO ENGINE RPM n CENTRIFUGAL FORCE THROWS WEIGHTS OUT n ALLOWS SPARK TO HAPPEN SOONER TO ALLOW ENOUGH TIME FOR COMBUSTION TO TAKE PLACE ON POWER STROKE. FIG 5-34

VACUUM ADVANCE n Provide advance at lower engine speeds and part throttle operation n Matches timing to engine load n Controlled by venturi vacuum or manifold vacuum FIG 5-35

ELECTRONIC SPARK TIMING n Distributor does not have a centrifugal or vacuum advance mechanism n Uses engine sensors as inputs to computer n You must disable spark advance when setting base timing on computer controlled cars

DISTRIBUTORLESS IGNITION SYSTEM

ENGINE FIRING ORDER n REFERS TO SEQUENCE SPARK PLUGS FIRE n CAST INTO INTAKE MANIFOLD n EACH ENGINE WILL HAVE DIFFERENT FIRING ORDER n MUST USE DURING TUNE-UP FIG 5-3