Ignition Coil

The Ignition coil functions as an energy-storage device and transformer. It is supplied with DC voltage from the alternator, and provides the high tension ignition pulses for the spark plugs.
The MFI engine adopts a computerized ignition system. The ECM calculates ignition timing, timing advance, and knocking control by the sensor signals.
There are distributor type and distributorless types in the ignition system.
(1) Distributor Type
In the distributor type, high voltage is generated at the ignition coil. It is distributed to 4 cylinders using the distributor. In general, the primary coil is controlled by the power transistor.
Therefore, energy is charged in the primary coil while the transistor is on. High voltage generates at the secondary coil when the transistor turns off. Then high voltage is distributed to the spark plugs by the distributor.
(2) Distributorless Type
2 or more of the ignition coils are installed in the distributorless type. The ECM directly controls the primary coil, and the High voltage is distributed to each cylinder without a distributor.
In the distributorless type, sometimes the primary coil is controlled by the power transistor. In that case, the power transistor is installed inside the ignition coil. The operations of the ignition coil and power transistor are the same as that of distributor type.
The checking method of the ignition system is as follows:

• Spark test:
  To perform the spark test, remove the high-tension cable from the spark plug, and check the spark generation from the high-tension cable.
  For reference, when engine idle condition is not good, remove the high-tension cable of each cylinder one by one and perform power balance test, which compares the engine condition. Through this test, we can find the trouble cylinder, and we can solve the problem by inspecting the fuel system, ignition system, combustion chamber pressure, which may influence on the combustion in the corresponding cylinder.


• Checking the coil resistance:
  To check the coil resistance, remove the coil connector and measure the primary coil resistance at the connector. As for the secondary coil resistance, remove the high-tension cable and measure the resistance of the secondary coil. Since each coil resistance value differs depending on the engines, please refer to the shop manual for the correct values.


• Measuring the waveform of primary ignition coil in cranking or idle state:
  To check the waveform, measure it at the primary coil. The waveform at the primary coil on timing should looks like the waveform on the screen. If not, check the battery voltage, ground condition, spark plug, and high tension cable and power transistor.

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