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Ignition Switch
Ballast Resistor
Dist Cap and Rotor
Ignition Wireset
Dielectric Grease
Wire Looms
Firing Order
Spark Plugs
Ignition Coil
Pickup Coil
Ignition Module
Ignition Timing
Vacuum Advance / Retard
Mechanical Advance
Select a part to view solution for common problems associated with the item.
Operation: The battery has four main functions. It supplies the energy to operate accessories when the engine is not running, it supplies the energy to crank the engine, it provides additional energy when electrical demands exceed the abilities of the charging system, and it acts as a voltage stabilizer absorbing voltage fluctuations in the system. Advice: Corroded, dirty, or loose battery terminal connections can cause problems in the ignition system. If a bad battery is suspected, remove the battery from the vehicle, clean the terminal posts, top off the electrolyte levels if accessible, fully charge the battery and then load test it.
Operation: The ignition switch is an integral part of the electrical system. The majority of automotive system components do not receive any electrical current unless the ignition switch is on. Advice: It is possible for a faulty ignition switch to cause problems in the ignition system, however if a faulty ignition switch is the cause of an ignition system problem, there will probably be other ignition switch related symptoms as well.
Operation: The ballast resistor is designed to drop battery voltage going to the ignition coil from 12 volts to 9.6 volts. The lowered voltage decreases the operating temperature of the ignition coil, extending its life. Advice: When a ballast resistor goes bad it will usually cause an open circuit. If the ballast resistor is suspected to be bad, check for voltage before and after the resistor. You should find battery voltage before the resistor and approximately 9.6 volts after the resistor.
Operation: The distributor has a rotating shaft that is usually driven by the camshaft. It is designed to distribute the high voltage pulses generated by the ignition coil to each of the spark plugs exactly when needed. Older distributors housed the points and condenser as well as mechanical and vacuum operated advance and retard mechanisms. The electronic ignition distributor often houses the pickup coil and ignition module and in some cases the ignition coil. Advice: Before removing the distributor take note of the orientation of the distributor body as well as to the direction that the rotor is pointing so that when you reinstall the distributor you can get it as close as possible to where it was originally. Some distributors due to the design of the drive gear will turn the rotor slightly as you lift it out of the bore. Keep this in mind when reinstalling, you will have to start with the rotor slightly turned from where you want the finished installed position to be. If the engine crankshaft is rotated while the distributor is out of its bore, you will need to bring number one piston to top dead center of its compression stroke and install the distributor so that the rotor is pointing to the number one tower on the distributor cap. If in doubt, follow the procedures outlined in the repair guides for reinstalling the distributor. Some distributor drives are designed with slotted offsets to mesh with the camshaft in only one way. This makes reassembly much easier. Always check and adjust the ignition timing any time that the distributor is disturbed. Recommendations: Repair guides
Operation: The distributor cap and rotor work together to route the high energy voltage pulses created by the coil to each of the spark plugs in proper order. Advice: Over time, the electrical contacts will become worn and burnt and the distributor cap and rotor will need to be replaced. Some other things to look for when examining the cap and rotor include physical defects such as cracks, burnt markings and carbon tracking which resembles a thin pencil line running from one contact to another.
Operation: The ignition wire-set is responsible for carrying the high energy voltage pulses created by the coil to each of the spark plugs. Advice: The correct firing order is critical to engine operation. If an ignition wire is hooked up to the wrong plug, there is at least one other plug that is wrong too. This is referred to as crossed wires. The best way to ensure against crossed wires is to replace them one at a time. Start with the longest wire, and work your way one by one down to the shortest wire. If in doubt, the repair guides are a good source for the ignition wire-set routing information. Remember, corrosion prevention is much easier than corrosion removal. Apply a small amount of dielectric grease to the terminals on each end of the ignition wires prior to installation. Recommendations: Dielectric Grease Repair guides
Operation: Dielectric grease is an insulating grease. It helps to keep corrosion causing moisture out of an electrical connection. Advice: Corrosion prevention is much easier than corrosion removal. Apply a small amount of dielectric grease to the terminals on each end of the ignition wire prior to installation. Recommendations: Dielectric Grease
Operation: Wire looms are designed and placed to route the high voltage ignition cables. Advice: Correct ignition cable routing is important not only for keeping the cables away from hot or moving objects, they are also configured to reduce the possibility of crossfire due to induction across misrouted ignition cables. Recommendations: Replace any missing or broken wire looms.
Operation: The offsets on an engines crankshaft are designed so that the power stroke of one piston forces the next piston in the firing order up on its compression stroke. The firing order is derived from the design of the crankshaft and is critical to smooth engine operation If an ignition wire is hooked up to the wrong plug, there is at least one other plug that is wrong too. This is referred to as crossed wires. Advice: The best way to ensure that your firing order is correct is to replace the spark plug wires one at a time. Start with the longest wire, and work your way one by one down to the shortest wire. If in doubt, the repair guides are a good source for information on the firing order and ignition wire-set routing. Recommendations: Repair guides
Operation: The spark plugs provide an air gap for the high voltage surge coming out of the coil to jump across. The resulting spark is what ignites the air fuel mixture. Advice: With the use of precious metals such as platinum, spark plugs are designed to last a lot longer than they used to. A set of double platinum plugs are supposed to last as long as 100,000 miles providing the air fuel mixture is kept properly at a 14.7 to 1 ratio. The platinum keeps the electrode from eroding, which gives it it's longevity but a rich air fuel mixture will still foul one out quickly. Some spark plugs are tucked away in some pretty hard to get to areas. Swivel and sometimes double swivel sockets are needed to reach them. A plug boot from an old ignition wire set makes a good plug starter. A � inch drive extension will slip nicely into the end of the old plug boot if you need a little extra reach. When removing the old plugs, lay them out in order so that if you have one or two that are burning differently than the rest you can identify which cylinders are involved. Put a small amount of anti-seize compound on the threads of the new plugs. This will help when it comes time to remove them the next time. Recommendations: Swivel spark plug sockets Anti-seize compound
Operation: The ignition coil amplifies normal battery voltage that is fed into its primary windings to create high voltage pulses that are needed to fire the spark plugs. Advice: The testable parts of an ignition coil are the primary and secondary windings. The primary winding in an average coil consists of a piece of wire looped two to three hundred times around an iron core. Battery voltage passing through these hundreds of loops creates a magnetic field which emits out across the secondary windings. A magnetic field passing over a wire will induce a voltage in that wire. The secondary winding consists of a piece of very fine wire looped twenty to fifty thousand times. The more loops that are present in the winding the higher the voltage that is being induced will be. When current passing through the primary winding is shut off by the opening of the points or in the case of electronic ignition by the switching of a transistor in the ignition module, the magnetic field collapses. The high voltage that has built up in the secondary windings needs to find its way to ground. That path to ground is provided by the spark plug wire and spark plug. The spark that is created by the high voltage pulse jumping the gap at the end of the spark plug is what ignites the air fuel mixture driving the piston down. That being said, other than measuring secondary voltage output under operating conditions which requires an oscilloscope, the only tests that can be run on an ignition coil is to verify the integrity of the two windings of wire inside. Excessive resistance, or an open circuit in one of the windings are the two most common ignition coil failures. All ignition coils have a resistance specification measured in ohms, for both primary and secondary windings. If the ohms measurement for either the primary or secondary windings on the coil you are testing falls outside the parameters of the specification, it needs to be replaced. Recommendations: Volt / Ohm meter
Operation: The job of the pickup coil is to tell the ignition module when to interrupt the flow of current passing through the primary windings of the ignition coil. Advice: Over the years several devices have been used to trigger the high voltage pulse coming out of the ignition coil. Early models used a conventional point set that physically opened and closed a set of contacts, The distributor shaft was fitted with a cam that had a lobe for each cylinder. As the cam turned the lobes or high spots would open and close the contacts on the points set. With electronic ignition a transistor is used instead of the physical points set. The transistor is switched on and off by the ignition module according to the signal it receives from the pickup coil. The pickup coil uses an electromagnet incorporated with a reluctor and stator. The reluctor and stator have several trigger points, one for each cylinder. The stator spins on the distributor shaft inside of the reluctor. Each time the trigger points on the stator line up with the trigger points on the reluctor a voltage pulse is induced and sent to the ignition module which then switches the transistor on or off. Another method of triggering the ignition module is with a hall effect switch. This method uses a stationary electromagnet with a gap between the north and south poles. A cylindrical metal shield that rotates with the distributor shaft passes through the gap. This metal shield has strategically positioned gaps (one for each cylinder) incorporated into the design. As the distributor rotates the shielding and un-shielding of the gap triggers the ignition module to switch the transistor on or off. Fine tuning this design a little further brings us to the optical distributor. This design uses the shielding and un-shielding method, only instead of using magnetism the gaps allow and block the transmission of a beam of light between a light emitting diode and an optical receiver. Also, instead of one gap per cylinder there are 360 small holes, one for each degree of rotation. Now the computer can tell exactly when to trigger the high voltage pulse by how many degrees of rotation the distributor is at.
Operation: The job of the ignition module is to control spark timing. Advice: Each time that the ignition module turns the current flow through the primary windings of the ignition coil off, a high voltage pulse is emitted from the secondary windings of the ignition coil. The amount of time that the current flow is on versus the amount of time that the current flow is off is known as the dwell angle. Changing the dwell angle also changes the ignition timing. By manipulating the on and off times the ignition module not only fires the coil at the correct time it can also make small adjustments to the ignition timing for tweaking the power curve as well as correcting for spark knock. Whenever possible test the old part before replacing it. AutoZone has the tools to test many ignition modules. Check the Wells Engine Management test sheets to see if the part number for the ignition module you are trying to test is supported with a test procedure. Recommendations: Wells tester
Operation: Setting the ignition timing refers to the process of rotating the distributor until number one cylinder is firing it's sparkplug at precisely the correct time according to engine specifications. Advice: A difference of 2 degrees of distributor rotation can make a big difference in how the engine performs. On vehicles with mechanical points ignition, it is important to remember that dwell will effect the timing. So set the points gap first. On vehicles with electronic ignition, the first step is to disable any advance or retard mechanisms. Disabling a vacuum operated advance / retard mechanism. On older vehicles this can be accomplished by removing and plugging the vacuum hose(s) from the distributor's vacuum advance / retard mechanism, and lowering engine RPM to a point below the threshold of the centrifugal advance. Vehicles with computer controlled advance. On computer controlled vehicles the advance mechanisms are disabled by temporarily taking the computer out of the loop. Different manufacturers accomplish this in different ways. Ford vehicles use a spout connector that you disconnect. GM uses a single wire connector. When this wire or spout connector is disconnected, the advance and retard signals are blocked and base ignition timing can be set. The under hood emissions decal will show the procedure. If it is missing or no longer readable, check the repair guides for the correct procedure for the vehicle you are working on. Setting the timing. After the advance and retard mechanisms are disabled, connect the inductive pickup on the timing light to #1 spark plug wire, and the positive and negative battery clamps to their respective battery terminals to power the light. Loosen the distributor hold down clamp slightly. With the engine running at the specified RPM, point the timing light at the timing marks and rotate the distributor until the correct timing is obtained, then shut the engine off, tighten the distributor hold down clamp and re-enable the advance and retard mechanisms.
Operation: The vacuum advance uses a vacuum diaphragm to physically move the breaker plate inside of the distributor advancing the ignition timing as needed depending on engine load. Some vacuum advances have dual vacuum chambers which allow them to retard the timing as well as advance it. Advice: To test the vacuum advance / retard mechanism, connect a vacuum pump to the port(s) and apply approximately 15 inches of vacuum. You should see the breaker plate move with the application of vacuum and hold as long as vacuum is applied. If the advance / retard mechanism does not hold a vacuum it needs to be replaced. If the breaker plate fails to move, the advance / retard mechanism may be faulty or the breaker plate may be physically stuck. Check the repair guides for the vehicle you are working on for removal and replacement procedures. Recommendations: Repair guides
Operation: The mechanical or centrifugal advance uses a system of levers and weights held in place by spring tension. As the distributor shaft spins, the centrifugal force slings the weights outward against their spring tension. As the weights move out they move the levers that are attached to the rotor. This changes the position of the rotor and affectively changes ignition timing as needed depending on engine RPM. Advice: With the distributor cap removed you should be able to slightly rotate the rotor and see the movement of the mechanical advance. If no movement is seen the mechanical advance may be stuck. A mechanical advance that is stuck can result in poor performance as well as poor gas mileage.
*This image does not represent the actual look of your selected vehicle. Please refer to any car manual to see specific part.