Even distributorless ignition systems have spark plugs, ignition cables, coils and modules. The only parts missing are the distributor cap and rotor. Instead of a single ignition coil, most distributorless ignition systems have at least one coil for every two cylinders and some have a separate coil for every cylinder!

There are two primary reasons people buy ignition parts: one is to hopefully "cure" an ignition-related driveability problem (which more often than not turns out not to be ignition-related). The other is for scheduled maintenance.

The spark plugs deliver the spark that ignites the fuel mixture as the piston approaches top dead center on its compression stroke.

Whenever a plug misfires, a whole cylinder of unburned fuel goes out the exhaust pipe. Not only does this waste a lot of fuel, it makes the converter work extra hard to get rid of the unwanted hydrocarbons in the exhaust. If the occasional misfire turns into a steady misfire, the result can be an overheated converter and a possible meltdown. Even if the converter doesn't cook itself, the engine will be noticeably down on power. It may idle rough, be hard to start and will likely fail an emissions test. The cure would seem to be a new set of plugs.

But life is never so simple. First of all, there's a reason why the plugs are misfiring in the first place. The underlying problem could be bad ignition cables, a weak coil or even a fuel problem. A condition known as "lean misfire" occurs if the air/fuel mixture is too lean to ignite reliably. This can be caused by clogged fuel injectors, vacuum leaks or an EGR valve that's stuck open.

In situations where the old plugs have umpteen zillion miles on them, they're probably misfiring because the electrodes are badly worn.

The recommended replacement interval for most spark plugs, except the long-life variety, is still 30,000 miles. The vehicle manufacturers claim their long life plugs can go 100,000 miles, but that's assuming ideal circumstances.

To produce a nice, hot spark for reliable ignition, the electrodes must be sharp, clean and gapped at the proper distance apart. As the plugs wear, the electrode gap widens because of metal erosion.

The edges of the center electrode can become rounded, making it harder for the spark to find an easy path to ground. This increases voltage demands on the ignition system, which may not be able to provide the necessary voltage under all conditions. So the engine starts to misfire - typically when it is under load, accelerating or running at higher speeds.

A more common cause of plug misfire is the presence of fouling deposits on the electrodes and center insulator. All plugs accumulate deposits so all are designed to be self-cleaning - assuming the plug gets hot enough to burn off the unwanted deposits. Even so, deposits can build up if a vehicle is only used for short trips around town and is rarely driven at highway speeds.

Stop-and-go city traffic and prolonged idling are really bad in this respect because both encourage deposit buildup. Today's copper-core spark plugs with their broad heat range do a good job of keeping themselves clean, but even the best plug can succumb to deposits under these kind of driving conditions.

The buildup occurs even more quickly if the engine is using oil. Eventually the deposits will bridge the electrode gap or provide a conductive shortcut to ground that bleeds off the voltage before it can form a spark.

Replacing a fouled set of plugs will buy time but under the same operating conditions fouling will eventually claim the new set of plugs, too. One way to extend the life of the plugs is to go to a hotter heat range. A hotter plug is a cleaner running plug.

You might therefore recommend such a plug to customers who spend the majority of their time sitting in traffic, idling or making short trips.

The drawback of a hotter plug is that it may promote detonation or preignition if the engine is operated under high loads (pulling a trailer, for example) or driven at sustained high speed. For these types of driving applications, a colder plug would serve your customer's needs better.

There are a lot of different types of spark plugs to choose from these days, partly because of advances in spark plug technology, and partly because of how some plugs are marketed. In addition to standard replacement plugs and premium long-life plugs, there are also "truck" plugs and performance plugs. The main feature of a performance plug is a unique electrode configuration that reduces misfires.

When looking up replacement plugs, refer to the year, make, model and engine displacement to make the correct selection. Replacement plugs must have the exact same thread size, seat style (tapered or flat) and reach (how far the plug extends into the combustion chamber) as the original. Resistor plugs must also be used where specified to prevent electromagnetic interference that can affect both radio reception, engine computer and other onboard electronics.

Most spark plugs are pregapped at the factory and are ready to install but you should still look up the recommended plug gap for your customer and remind him or her to check the gap.

IGNITION CABLES. The ignition cables carry the voltage from the coil to the spark plugs. The secondary voltage may range anywhere from 5,000 up to 25,000 or more volts per spark depending on engine load, speed, plug gap and operating temperature. If the cables lose some of this voltage along the way or don't allow it to reach the plugs with full force, the plugs will misfire.

As cables age, the insulation may become brittle or cracked leading to voltage losses and shorts. Rough handling, atmospheric heat, and vibration and heat can all accelerate the aging process, as can excessive heat.

If the insulation around the cables is deteriorated, burned, chaffed, cracked or otherwise damaged, the cables need to be replaced. The same is true if a cable's internal resistance exceeds manufacturer's specifications.

Replacement cables may be sold individually or in sets. If a customer needs more than one wire, he should probably buy an entire set. Some manufacturers even recommend replacing the cables every 30,000 to 50,000 miles for preventative maintenance.

Various types, as well as sizes, (7mm & 8mm) of replacement plug wires are available, so it's important to know something about each type:

Distributed resistance wire cable has a fiber glass core impregnated with Latex graphite, and is the type of wire used as original equipment on most domestic and import vehicles. This type of wire provides the maximum amount of radio frequency interference (RFI) suppression, and is required on all late model vehicles with computerized engine control systems. RFI is created when high voltage passes through the plug wires.

Creating a controlled amount of resistance in the wire suppresses RFI. RFI is regulated by the government to prevent interference with radio, television, two-way radio and cellular phone signals.

Fixed resistor wire has a steel or copper metallic core with a fixed resistor in the plug boot to control RFI. This wire is commonly used on European imports.

Inductance wire, also called "mag wire," is internally wrapped with nickel alloy steel. Some aftermarket mag wire does not meet OEM specifications for RFI because it only has about 300 to 750 ohms of resistance per foot. This does not provide a "hotter spark" as some manufacturers claim.

The type of insulation used in a plug wire is also important. Many premium wire sets use a silicone jacket, which can withstand temperatures of up to 480 degrees F, with an inner layer of EPDM (Ethylene Propylene Diene Monomer) insulation which can withstand temperatures of up to 350 degrees F (80 to 110 degrees higher than Hypalon). Others use an outer jacket of EPDM, or a covering of EVA (Ethylene Vinyl Acetate), which also provides high temperature protection.

COILS, CAPS AND ROTORS. Ignition coils are pretty reliable and aren't replaced very often. Even so, they can be damaged by heat, vibration and voltage feedback from open or loose plug wires. A weak coil may not be able to produce sufficient voltage to fire the plugs under all conditions, so if it doesn't meet manufacturer's specifications it needs to be replaced.

On some DIS systems, coils may be replaced individually while on others the coils are part of an assembly and must be replaced as an entire unit.

As for caps and rotors, there is no recommended replacement interval so these parts are typically replaced on an "as needed" basis. Caps and rotors erode over time, and can crack or develop carbon tracks that created unwanted paths for the voltage to follow.

One other part you may be asked to look up is a ballast resistor. This device is used on many older ignition system to reduce the primary voltage to the ignition coil after the engine has started. A failed ballast resistor will prevent the coil from firing.

ELECTRONIC IGNITION COMPONENTS. The rule here is that either these parts work or they don't - sometimes! Electronic parts can fail without warning. One minute everything's fine, the next minute the engine dies and won't restart. Intermittent problems can be especially vexing because they come and go. These tend to be temperature or moisture related, and are usually caused by opens or shorts.

Replacement ignition modules are application specific on many vehicles because of differences in timing curves. So just because a replacement module looks the same as the old one, it's no guarantee it will work correctly. Always follow the module suppliers vehicle application listings.

Ignition modules that are mounted inside or on a distributor typically require dielectric silicone grease on the underside to aid heat transfer. Forget the grease and the replacement module may be short lived.

Ignition pickups come in three basic types: magnetic impulse, Hall effect, and optical. Magnetic pickups are commonly used on older domestic passenger cars, with Hall effect pickups more common on later model applications. Optical systems are found only on certain imports and '92 through '96 Corvettes.

Magnetic pickups generate an AC voltage signal that the ignition module uses to fire the ignition coil.

A Hall effect pickup generates a digital DC signal for the same purpose, while the optical systems use a shutter blade, light emitting diode (LED) and photo receptor to generate a digital DC signal.

On most distributorless ignition systems, a crankshaft position sensor (either magnetic or Hall effect) serves the same purpose as the pickup in a distributor ignition. The signal from the crankshaft position sensor goes to the coil pack module and/or powertrain control module to trigger the coils.