The vacuum advance increases FUEL ECONOMY because it helps maintain idle fuel spark advance at all times. It is a method of matching ignition timing with engine load. The vacuum advance provides additional spark advance when engine load is low at part throttle position. This causes the ignition coil to fire with the engine pistons not as far up in the cylinders. The action of the centrifugal advance causes the contact points to open sooner, or the trigger wheel and pickup coil turn off the ECU sooner. At a preset engine speed, the lever strikes a stop and centrifugal advance reaches maximum. With this design, the higher the engine speed, the faster the distributor shaft turns, the farther out the advance weights move, and the farther ahead the cam or trigger wheel is moved forward or advanced. This movement causes the distributor cam or trigger wheel to move ahead. Timing stays at its normal initial setting.Īs speed increases, centrifugal force on the weights moves them outwards against spring tension. At this time there is not enough centrifugal force to push the weights outward. Basically the centrifugal advance consists of two advance weights, two springs, and a advance lever.ĭuring periods of low engine speed, the springs hold the advance weights inward towards the distributor cam or trigger wheel. This action helps correct ignition timing for maximum engine power. Spark timing is advanced by rotating the distributor cam or trigger wheel against distributor shaft rotation. VACUUM ADVANCE (controlled by intake manifold vacuum and engine load)ĬOMPUTERIZED ADVANCE (controlled by various sensors- speed, temperature, intake, vacuum, throttle position, etc.)Ĭentrifugal advance makes the ignition coil and spark plugs fire sooner as engine speed increases, using spring-loaded weights, centrifugal force, and lever action to rotate the distributor cam or trigger wheel. The basic methods to control ignition system timing are as follows:ĬENTRIFUGAL ADVANCE (controlled by engine speed) Timing retard prevents the fuel from burning too much on the compression stroke, which would cause spark knock or ping. Spark retard is required at lower speeds and under high load conditions. Timing retard happens when the spark plugs fire later on the compression strokes. More time advance is required at higher speeds to give combustion enough time to develop pressure on the power stroke. The timing is set several degrees before top dead center (TDC). Timing advance happens when the spark plugs fire sooner than the compression strokes of the engine. Ignition timing must vary with engine speed, load, and temperature. Ignition timing refers to how early or late the spark plugs fire in relation to the position of the engine pistons.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |