Advance Essentials: Automotive Ignition System Basics

Automotive Thermostat Fully mechanical distributors used a tall
round ignition coil to generate firing voltage.

Troubleshooting your automotive ignition system is intimidating since most electronic ignition systems have gone through major changes over the years. Though the latest versions of car ignition systems look different from their predecessors and use components with fancy-sounding names, they all work on the same basic principles. By understanding automotive ignition system basics, you can fix any of them, even the fully computerized versions. The many different variations of automotive ignition systems all boil down to three types: distributor-based, distributor-less, and coil-on-plug. Let’s look at the similarities of each automotive ignition system.

All automotive ignition systems have to generate a spark that’s strong enough to jump across the spark plug gap. To do that, all automotive ignition systems use an ignition coil made with two coils of wire wrapped around an iron core. The goal is to create an electromagnet by running battery voltage (12 volts) through the primary coil. When the car ignition system turns off the power, the magnetic field collapses. As it does, a secondary coil captures the collapsing magnetic field and converts it into 15,000 to 25,000 volts. There you have it. Turn power on. Turn power off and get spark. Now buckle up; here’s where things get complicated.

In order to get maximum power from the air/fuel mixture, the spark must fire at just the right moment during the compression stroke. Engineers have used several methods to control spark timing. The early systems used fully mechanical distributors. Next came hybrid distributors equipped with solid-state switches and ignition control modules (low-end computers). Then, engineers designed fully electronic automotive ignition systems. The first fully electronic ignition system was the distributor-less style (DIS). The latest automotive ignition systems are called coil-on-plug (COP). In addition to improving spark timing, the newer ignition systems use redesigned ignition coils that pack a much bigger wallop to make a hotter spark. Let’s now examine each type of automotive ignition system more closely.

The distributor automotive ignition system

Automotive Distributor This mid '80s Ford distributor used a rotating
disc with cut out windows.

Distributor-based automotive ignition systems connect to the camshaft with gears. In the fully mechanical distributor, the gears spin the main distributor shaft. Inside, a set of “ignition points” rubs against a multi-sided cam on the distributor shaft. The cam opens and closes the points. That’s what starts and stops the flow of power to the ignition coil. Once the coil generates firing voltage, it travels to the top of the coil and into the top of the distributor cap. There, a rotating disc attached to the distributor shaft “distributes” the power to each of the spark plug wires.

These fully mechanical distributor systems had its shortcomings. The ignition points would break down and change spark timing, messing up engine efficiency and requiring replacement as often as every 12,000 miles. So engineers ditched the fully mechanical distributor and incorporated solid-state switches that didn’t wear out. That increased reliability. But the solid-state switches still took their marching orders from the distributor shaft — and that distributor shaft was still mechanically driven from the camshaft. Since gear wear would always be an impediment to proper spark timing, mechanical ignition systems had to go. So starting in the early ’80s, engineers dumped the mechanical distributor and started using a distributor-less automotive ignition system (DIS).
If your vehicle has a fully mechanical distributor and you’re not getting spark, start your diagnosis by replacing the ignition points and condenser. They’re the most likely culprits and luckily are inexpensive. But make sure to reach for quality auto parts such as the kind you’ll find at Advance Auto Parts. If you’re doing a tune-up on this type of car ignition

Fully mechanical distributors Fully mechanical distributors used a tall
round ignition coil to generate firing voltage.

system, replace the rotor, and distributor cap too. Once again make sure you install quality auto parts. Tuning up a hybrid distributor? Replace those same parts and include a new set of spark plug wires. If you’re not getting spark on a hybrid distributor system, it could be a faulty ignition “pick-up” sensor inside the distributor or a bum ignition module. Consult a repair manual for the testing procedure and test the components with a digital multi-meter. The testing procedure is easy. If you isolate the problem to the pick-up sensor, don’t replace it. It’ll take hours to disassemble the old distributor in order to remove the sensor. Instead, spend a few more bucks and buy a completely rebuilt distributor. Then just pop it in place and set the timing. Just like our advice for buying points, condensers, distributor caps and rotors, it’s important to buy high quality auto parts for your electronic ignition system distributor from Advance Auto Parts.The distributor-less automotive ignition system (DIS)

The DIS determines spark timing based on two shaft position sensors and a computer. The Crankshaft Position Sensor (CKP) mounts at the front of the crankshaft (or near the flywheel on some makes). The Camshaft Position Sensor (CMP) mounts near the end of the camshaft. The sensors constantly monitor both shafts’ position and feed that positioning information into a computer. In addition to changing how these systems “time” the spark, the DIS also employs a different coil

setup. Instead of asking a single coil to power all the cylinders, the DIS uses multiple ignition coils called “coil packs.” A DIS coil generates spark for only two cylinders. So each coil can be “on” longer and develop a stronger magnetic field. When the ignition control module or PCM turns the power off, this stronger field produces about 30,000 volts. Engineers needed that stronger hotter spark to ignite the newer leaner fuel mixtures.


If a DIS won't fire, don’t troubleshoot the ignition system by replacing the ignition control module or the PCM. They’re the least likely culprits and they’re the most expensive. Instead, check out either the CKP or the CMP sensor—they have the highest failure rates of all parts in your electronic ignition system. Consult a repair manual for the testing procedure and conduct the tests with a digital multi-meter. If you’re tuning up a DIS, make sure you replace both the spark plugs and the spark plug wires with quality auto parts.

Goodbye spark plug wires. Enter the Coil-on-plug ignition (COP) car ignition system

A coil-on-plug (COP) car ignition system incorporates all the electronic controls found in a DIS car ignition system. However, instead of two cylinders sharing a single coil, each COP coil services only one cylinder so the coil has twice as much time to develop maximum magnetic field. The result? Some COP car ignition systems generate as much as 40,000 to 50,000 volts.

COP car ignition systems have another huge advantage over DIS car ignition systems. Since the coil mounts directly on top of the plug, it doesn’t require spark plug cables. Instead, it delivers firing voltage directly to the plug. If you’re replacing spark plugs on a COP car ignition system and those COP coils use a detachable spark plug boot, replace the boot with a new one. You can count on the high-quality auto part boots found at Advance Auto Parts to prevent needless misfires.

Here’s another tip: if you get a cylinder misfire code on a COP electronic ignition system, troubleshoot the car ignition system by swapping the coil from the suspected cylinder with a coil from a different cylinder. If the misfire moves to the swapped cylinder, you’ve nailed the culprit.

Finally, we’ve seen many COP coils fail right after an engine cleaning, so if you plan to degrease your engine, start by wrapping each COP coil with plastic wrap (remove it when you’re done). Then avoid spraying degreaser or water anywhere near the coils.

Recommended Tune-Up Parts
We cannot stress enough the importance of always using quality auto parts. When you include Advance Auto Parts during your car ignition system troubleshooting tasks, you help ensure that you get the job done correctly and quickly.

Spark plug wires
For best performance and highest gas mileage, always replace your automotive ignition system’s spark plug wires as a complete set when replacing spark plugs.


Distributor cap and rotor
“Carbon tracking” can cause car ignition system misfires and poor performance. That’s what happens when the carbon "button" at the top of the car ignition system distributor cap wears down and the rotor distributes the carbon around the inside of the cap. To eliminate those problems, just replace the cap and the rotor when you change plugs.


Replacement COP boots
Some COP car ignition systems are equipped with replaceable spark plug boots. As the boot deteriorates from the high voltage and heat, firing voltage can leak out and cause misfires. Always replace the boot and the spring when working with those coils.


Spark plug wobble sockets
Buy a spark plug socket with built-in wobble to fit into tight spaces. They take up less room than an ordinary spark plug socket that has an added wobble extension and makes plug removal easier.


Spark plug socket with swivel locking extension
This GearWrench spark plug socket with swivel locking extension provides maximum turning angle and the most clearance for tight spaces. The socket and extension are permanently locked together so it’ll never disconnect from the socket as you remove the plug.


Flexible handle ratchet
You need plenty of angles when you’re trying to remove spark plugs from tight spaces. When you combine this flex-head ratchet with a wobble spark plug socket or a swivel socket with locking extension, you can remove spark plugs in less time and with less sweat.


Spark plug gap gauge
Always gap spark plugs to the manufacturer’s specifications before installing them.


Torque wrench
Spark plugs must be torqued properly during installation or you risk major engine damage. Over-tightening can rip the threads right out of the aluminum cylinder head and can distort the body of the plug, causing it to leak. Under-tightening can cause the plug to loosen, leak combustion pressure and even blow the plug right out of the head, taking the threads with it. Buy a ft-lb. torque wrench and get the tightening specs from the spark plug manufacturer’s web site. 


Spark plug boot grease
Squirt a dollop of spark plug boot grease into the boot. Then install the boot on the spark plug. The dielectric grease prevents ignition system high voltage “flashovers” (voltage leaking out of the boot to ground) and makes future boot removal easier.


Spark plug boot puller pliers
Spark plug boots tend to “weld” themselves to the plug. Pulling directly on the wire can damage the connection and separate the wire from the boot. Use a pair of spark plug boot puller pliers to grab the boot and break it loose, then use it again to pull the boot off the wire.


Wire loom spacers
Spark plug wires are always spaced apart with plastic wire loom holders. Those plastic holders can break when you replace wires. Replace them so spark plug wires won’t touch and arc, causing misfires. 


Apply just a small drop of anti-seize to the spark plug threads (don’t get any on the electrodes or the porcelain). Then reduce the spark plug torque by about 10 percent. The anti-seize prevents the plugs from permanently bonding to the cylinder head threads.

Lastly, before you troubleshoot ignition system problems, always consult your owner’s manual first. Follow the manufacturer’s recommendations to ensure warranties are not voided.