FREE ASE PREP A8 – Automotive Primary Ignition:
This is another page from my ASE / BAR Smog License Course.
Automotive Primary Ignition was first introduce with the set of contact points on distributors, the cam lobe on the distributor mechanically open and close the primary circuit of the ignition.
Remember the Primary ignition triggers the Secondary ignition system from the negative side of the coil.
The amount of time the points are closed was referred to as dwell. Dwell is when the primary circuit of the ignition circuit is on and the coil is being charged or saturated in preparation to fire the secondary ignition.
As the emissions standards have gotten tighter, points were no longer feasible for the tighter emissions or to burn the leaner air fuel mixture.
Electronic ignition systems were introduced to control the Automotive Primary Ignition trigger to switch the primary circuit on and off.
The reluctor and the pickup coil perform the same function as the distributor lobe and points.
Also you have in some cases were some manufacturers are using the Powertrain Control Module “PCM” to control the primary ignition circuit to fire the ignition coil.
Many technicians, including myself are using an ammeter to check the ignition coil for current draw
Pick Up coil
The pickup coil is a permanent magnet which generates an AC current. When the reluctor tooth comes closer to the pole piece, the voltage increases. When the tooth and the pole piece are aligned, voltage drops to zero.
When the tooth moves pass the pole piece, the magnetic field reverses, and voltage increases in the opposite direction.
When the magnetic field collapses, mutual induction transfers energy from the primary windings into the secondary ignition windings were we get spark from the secondary circuit.
Note: Some ignition systems, for example the distributor-less ignition system may have more than one pick up coil
Hall Effect Sensor
Hall Effect switches in distributors are made up of a Hall element, a permanent magnetic and a shutter wheel that consists of alternating vanes and windows which pass between Hall Effect element and the permanent magnet.
As the shutter passes through the gap between the permanent magnet and the Hall Effect element it causes the voltage to change which in turn triggers the primary ignition circuit to trigger the secondary to fire the spark plugs.
The spark plug is where the high voltage electricity of the coil is distributed by the distributor to jump the gap to ground. If the plug is cracked, plug fouled, or gap closed the spark will be too weak to ignite the air fuel mixture.
Spark plugs come in different heat ranges installing a plug with the wrong heat range can cause problems, to cold of a plug will cause black soot on the plug and cause a misfire. To hot of a plug will cause the electrode to burn or even cause a detonation.
Once the Automotive Primary Ignition circuit triggers the coil, mutual induction transfer energy from the primary circuit to the secondary circuit to deliver spark. Spark has to travel from the ignition coil to the spark plug using a spark plug cable or cables.
Spark plug wires are highly insulated, so they can transfer the high voltage to the spark plugs and not short to ground before reaching the spark plugs.
At the end of the cable is an insulated boot that connects to the plug to prevent the high voltage in the wire from shorting to ground.
Automotive Primary Ignition
Spark Advance and Spark Retarded
At different speeds and loads, the Automotive Primary Ignition system must change when the ignition spark occurs in order to have the correct spark advance timing for operating conditions.
Spark advance is the position in degrees that a piston is at, Before Top Dead Center (BTDC).
Spark retard is the position in degrees that a piston is at, After Top Dead Center (ATDC).
Spark advance usually created by the vacuum advance front port, centrifugal or electronic control devices. The rear port is the retard side of the vacuum advance to help lower emissions at idle.
At idle the ignition occurs just before the piston reaches Top Dead Center (TDC). When the engine speed increases, the ignition spark must occur earlier so that ignition produces maximum pressure just as the piston passes TDC.
For better power, fuel economy and lower emissions the spark must occur earlier as the speed increases this will reduce Hydrocarbons (HC) and Oxides of Nitrogen (Nox).
The Automotive Primary Ignition circuit trigger is controlled by the ignition module or Power Control Modules (PCM) to open the primary ignition circuit.
Distributor-less Ignition System
Distributor-less Ignition System has electronic spark advance controls but do not have a separate distributor.
On the waste spark ignition system, there is one ignition coil for every two cylinders and there are other DIS systems that have more than one coil.
A Crankshaft Position Sensor signals is for crank shaft speed, and a Camshaft Position Sensor signal is for piston position to the ignition module or PCM
The Ignition Module (IM) or Power Train Control Module uses the information to deliver a spark at the correct time.
Some vehicles have a ignition sensor to detect misfires in the distributor-less ignition system, the sensor is usually placed near a rotating disc installed on the camshaft,crankshaft or crankshaft pulley.