Do I Need An External Igniter Module ?

Do I Need An External Igniter Module ?

How to identify if an ignition coil has an internal igniter module or will it require an external igniter.

How an ignition Coil Works

The following is an excerpt from Wikipedia and explains the operation of an ignition coil.

"An ignition coil consists of a laminated iron core surrounded by two coils of copper wire. Unlike a power transformer, an ignition coil has an open magnetic circuit — the iron core does not form a closed loop around the windings. The energy that is stored in the magnetic field of the core is the energy that is transferred to the spark plug.

The primary winding has relatively few turns of heavy wire. The secondary winding consists of thousands of turns of smaller wire, insulated from the high voltage by enamel on the wires and layers of oiled paper insulation. The coil is usually inserted into a metal can or plastic case with insulated terminals for the high voltage and low voltage connections. When the contact breaker closes, it allows current from the battery to flow through the primary winding of the ignition coil. The current does not flow instantly because of the inductance of the coil. Current flowing in the coil produces a magnetic field in the core and in the air surrounding the core. The current must flow long enough to store enough energy in the field for the spark. Once the current has built up to its full level, the contact breaker opens. Since it has a capacitor connected across it, the primary winding and the capacitor form a tuned circuit, and as the stored energy oscillates between the inductor formed by the coil and the capacitor, the changing magnetic field in the core of the coil induces a much larger voltage in the secondary of the coil. More modern electronic ignition systems operate on exactly the same principle, but some rely on charging the capacitor to around 400 volts rather than charging the inductance of the coil. The timing of the opening of the contacts (or switching of the transistor) must be matched to the position of the piston in the cylinder so that the spark may be timed to ignite the air/fuel mixture to extract the most angular momentum possible. This is usually several degrees before the piston reaches top dead center. The contacts are driven off a shaft that is driven by the engine camshaft, or, if electronic ignition is used, a sensor on the engine shaft controls the timing of the pulses.

The amount of energy in the spark required to ignite the air-fuel mixture varies depending on the pressure and composition of the mixture, and on the speed of the engine. Under laboratory conditions as little as 1 millijoule is required in each spark, but practical coils must deliver much more energy than this to allow for higher pressure, rich or lean mixtures, losses in ignition wiring, and plug fouling and leakage. When gas velocity is high in the spark gap, the arc between the terminals is blown away from the terminals, making the arc longer and requiring more energy in each spark. Between 30 and 70 milli-joules are delivered in each spark.

Primary Coil resistance is typically around 1.0 ohm.
Secondary Coil resistance is typically in the 4k to 10k ohm range.

Why an Igniter Module is Required For ECU Ignition Control

The current required to produce a spark with enough energy to run the engine correctly is far in excess of that which the ECU driver can supply.  Much like why a Relay is required to control high current devices with an ECU, the igniter module acts like a high speed relay.  It takes the signal from the ECU to trigger a driver that can handle the current required.

If a coil is connected directly to the ECU without an igniter module present it is highly likely that the ECU Ignition Driver will be damaged.

Methods for Identifying if There is an Igniter

Method 1: The Number of Connections

An ignition coil will always have at least two connections besides the spark plug lead connection.  These are normally labelled as a positive and a negative.  The Positive ( + ) is connected to 12V+ ignition power, and the Negative ( - ) is connected to the trigger source, in our case the igniter module.

Single Coils with 2x Pins

If the coil only has 2x pins then it does not contain an internal igniter module.  An external igniter is required.

A Bosch HEC coil without an internal igniter. The pins are labelled as positive (on right) and negative (on left).

Single Coils with 3x Pins

This refers to a single coil, not for a pack of multiple coils.

Often it is considered that if the ignition coil has 3x connection pins or more than it must have an internal igniter.  This is not always the case, in fact there are many common OEM ignition coils that have 3x pins and do not have an internal igniter.  Nissan, BMW, Audi and Volkswagen have a number of engines with ignition coils that are not built into the coil but the coils do have 3x pins.   Testing is required to verify if the coil has an internal igniter or not.

S13 and S14 coil with no internal igniter

-Igniter Module Trigger
+12V+ Switched
EGround (to head)

VW 1.8 Turbo coil with no internal igniter

Signal From Igniter
Ground (to cylinder head)
12V+ Switched

Coil Packs with 3x Pins

Coil packs that have more than one ignition coil but a single connector are not considered as the same number of pins as for single coils.  In the below example of a Subaru ignition coil there are 3x pins in the connector but there are actually 2x ignition coils joined together.   They are actually 2x coils with 2x pins each, but they share the 12V supply on one pin.  These coils therefore should be considered as a 2-pin type and as such they do not have an internal igniter, they actually have an external 2-channel igniter module.

Coil Pin
To Igniter Pin 5 (Cylinders 1+2)
12V+ Swtiched
To Igniter Pin 6 (Cylinders 3+4)

Single Coils with 4x pins or more

Haltech is not aware of any ignition coils that have 4x pins that do not have an igniter. 

A GM LS1 coil with 4x connection pins with an internal igniter

An IGN-1A coil with 5x connection pins with an internal igniter

Method 2: Primary Coil Resistance Test

This test involves using a multimeter and measuring the resistance between the 12V supply pin, and the Signal pin.

If there is continuity present and the resistance is around 1.0ohm, give or take a little, there is no igniter present.
If there is no continuity, then there is an igniter present.

Method 3: Primary to Secondary Coil Continuity Test

This test involves using a multimeter and measuring the resistance between the Signal pin and the coil discharge terminal.

If there is no continuity, then there is an igniter module present.
If there is resistance in the m-ohm range then there is an igniter present.
If there is resistance in the k-ohm range, and this is also approximately the same resistance between the 12V+ supply pin and the coil discharge terminal, there is no igniter present.
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