This month we look at how to use a coil on plug ignition system without using a cam sensor.

For the ECU to be able to fire the coils sequentially, a cam sensor must be used so the ECU can know if the cylinder is on the compression stroke or exhaust stroke.

However, sometimes the cam sensor isn’t available, either because the engine didn’t have one, or a choice has been made to simply not use one.

All our ECUs are designed to be able to switch between sequential ignition and sequential injection without changing the wiring or the values in the main tables.

Simply wire the signal wires to each of the ECU outputs as if the cam sensor is going to be available.

In the Coil Per Plug Settings, there are options to control the coil outputs.

If One Coil Per Plug is ticked, the ECU will look for a cam sensor, and use that to fire all the coils sequentially.

The number of coil outputs used is the same as the number of cylinders on the engine.

If One Coil Per Plug is not ticked, this tells the ECU that there is a wasted spark coil pack connected, so only the outputs required to fire this are used.

The number of outputs used is half the number of cylinders on the engine. If the engine has 4 cylinders, only the first two coil outputs will be used. If it’s a 6 cylinder, then only the first 3 coil outputs will be used, and so on.

However, our ECUs also have a feature called Twin Spark. This was designed to allow our ECUs to be used on genuine twin spark engines, where there are two spark plugs per cylinder. This simply ties the coil outputs together, depending on the number of cylinders on the engine.

There are various options, so a couple of examples will help to understand this.

Example 1

This engine uses a wasted spark coil pack to control each set of 4 coils.

This means One Coil per Plug is off, so outputs 1 and 2 are used for the first coil pack, and 3 and 4 are used for the second coil pack.

Example 2

This engine used one coil per plug, so One Coil per Plug is ticked on, and 8 outputs are required.

Outputs 1 to 4 fire the primary coils, and 5 to 8 fire the secondary coils.

Coil outputs 1 and 5 fire simultaneously, 2 and 6, 3 and 7, and 4 and 8 as well.

So, how do we fire one coil per plug without a cam sensor?

Simply wire them up as if there was a cam sensor, then set One Coil Per Plug to No, and tick Twin Spark.

The ECU now believes there are two wasted spark coil packs attached.

This means coil outputs 1 and 3 will fire together, and outputs 2 and 4 will fire together.

As there is no cam sensor, the ECU will fire the coils in a wasted spark mode.