Maximising Ignition Efficiency: The Role of Ignition Coils
Your car’s ignition system puts the spark in the spark plugs to ignite the fuel and air mixture to produce power. The battery supplies the initial voltage, and the ignition coil steps this up to roughly 40 thousand volts required for ignition.
With the demands placed on modern engines to produce more power from a smaller displacement, ignition coils (and ignition systems in general) have evolved to become more efficient and reliable and supply higher voltages. This means vehicles have moved on from older, mechanically driven distributor coils to electronically controlled systems.
Today we find coil packs, pencil or stick coils, coil-on-plug designs, and coil rails, but virtually all work on the same principle. Let’s delve deeper into the various types of ignition coils, how they work, and when it’s time to replace them.
The Basics of Ignition Coils
An ignition coil is essentially a step-up transformer. It consists of a primary winding, a secondary winding, and a laminated iron core. The battery current passing through the primary winding, consisting of fewer but thicker wires produces a magnetic field, and this is strengthened by the iron core.
When the circuit breaks, the magnetic field collapses and induces a high-voltage current in the secondary winding with thousands of thinner wore strands. This is passed on to the spark plugs via high-tension (H.T.) leads or connections. The process happens thousands of times each minute and generally corresponds to engine speeds.
Types of Ignition Coils
Distributor
These are found in older cars and rely on a mechanical distributor driven by the camshaft to deliver the high voltage sequentially to each spark plug. This coil type is simple and generally reliable, but it can’t muster the higher voltages (or stand higher temperatures) seen in newer cars. They were used until the early 1990s when they were replaced with various distributor-less types.
Ignition
Also called coil blocks, these contain several ignition coils in a single unit, and are connected by H.T. cables to each spark plug. They come in two configurations; single and dual spark technology.
In the first type, each ignition cable supplies the high-voltage pulse to one cylinder. One of the first applications was in the NA Mazda Miata, with the MX5 coil pack extracting all it can from the small displacement engines (and largely responsible for the crisp throttle response that made the car a lasting icon), while keeping fuel use and emissions to a minimum. The improved performance in coil packs is down to the fact that each spark plug is connected to its coil, and this leads to stronger sparks, more efficient combustion, and higher power output.
Dual spark systems have high voltage delivered to two cylinders (one in the compression stroke, the other in the exhaust stroke), producing one combustion spark and one support spark. These are different from “twin-spark” systems, with two plugs per cylinder.
Pencil
Pencil coils are an evolution of the distributor-less coil design since they have no ignition cables, but are attached directly to the plugs. This proves both practical as it saves space, and delivers better performance as no power is lost through the cables.
Ignition Coil Rails or “Systems”
These have multiple coils arranged along a rail and slotting directly on top of each spark plug. This too is a compact design but will require replacing the whole unit even if only one coil is damaged.
Upgrading the Ignition Coil in Your Car
The Miata mentioned above had rock-solid mechanicals, but it also had first-gen electrics that may have been borderline revolutionary at the time but surpassed in every way even by factory standard components used on the cheapest cars today.
To note, the stock ignition coil was one of the weakest links in an otherwise treat of a car and there was the odd hiccup, like the occasional misfires and black exhaust smoke indicating a backfire. This could be down to general wear and tear in higher-mileage cars meant to be driven to redlines.
Nevertheless, finding a new or reconditioned Mazda MX-5 coil pack with a bit more spark is straightforward. Even thirty years on, owners can get OEM packs to replicate the original performance or go with aftermarket versions if looking for more push.
The reasons to go with a performance aftermarket model in any car are the higher-rated voltage, improved throttle response, better consistency, and increased durability. Aftermarket coil packs are made to a higher standard with better materials that can not only induce higher voltage but also create a hotter spark.
Paired with “cold” plugs, this improves combustion efficiency with better burn rates. Moreover, the bags of voltage potential are there when you need them, either on the track or when tackling steep inclines.
The obvious reason, though, is that the aftermarket option will get more of any power additions you’ve done to the car. Miatas are some of the most modified cars out there, so swapping out even a decently functioning factory coil pack in a modified engine makes sense. The aftermarket version should balance out any potential timing and fuelling issues with mods in place (performance cams first come to mind) and is a necessity in turbos and superchargers.
How Long Do Coils Last?
Newer distributor-less coils ensure better timing efficiency, fewer moving parts, and fewer things that can go wrong. They evolved to address the need for better reliability and longevity, in addition to giving a performance boost with more precise ignition timing controlled by the ignition module and ECU.
Coils are rated to last for 100 thousand miles on average. This is in ideal condition and has no serious issues with other ignition and vehicle system parts. However, damaged or worn spark plugs and wires, excessive engine vibrations and heat, and moisture from oil leaks or condensation from the AC can all negatively affect performance and cause premature wear.
Signs the Coil Needs Replacing
A damaged coil will either produce very-low voltage and cause misfires or very-high voltage in order or overcome inherent issues with the spark plugs or wiring, eventually leading to overheating and short circuits. Diagnosing a faulty ignition coil is straightforward, as most issues are performance related:
-Misfires – weak sparks won’t ignite the air and fuel mixture, meaning the timing is off and leads to misfires. It can happen in one or all cylinders. Accompanying problems are engine judder and sudden loss of power.
-Backfiring – this is often an early symptom of failure and happens when unused fuel ignites outside the cylinders, most often in the exhaust system.
-Stalling and Hard Starts – the loss of power causes the car to stall. Starting is also difficult, with one single coil tasked to supply the required voltage for all plugs. If the car does start, there’ll be inconsistent idling.
-Higher Fuel Use – decreased combustion efficiency, and the inability of the engine to maintain the correct air and fuel ratios (since the voltage is insufficient for ignition), is the main cause of higher fuel consumption. Like backfiring, this is an early symptom of a faulty ignition coil.
-Check Engine Sign – misfires will throw up a check engine sign in the dash. Pinpointing the exact issue (and in which cylinder) is easy with an OBDII scan.
Buying Replacements
As mentioned, you can go with OEM or an aftermarket upgrade that should allow for improved ignition timing, crisper throttle response, and a slight power bump in unmodified engines. Prices vary and depend on the engine layout, type, brands, and perceived quality. Replacing coils is fairly simple if you know your way around cars and have basic tools. Otherwise, leave the work to a pro.