Knowledge of auto parts

How is the ignition coil diagnosed and tested

Ignition coils provide the high voltage needed by the ignition system to fire the spark plugs. Most engines that have a distributor ignition system have a single coil, but a few import applications have two coils. On distributorless ignition systems (DIS), multiple ignition coils are used. On "waste spark" systems, each pair of cylinders shares a coil. On other DIS and coil-on-plug (COP) ignition systems, each cylinder or spark plug has its own individual coil.
The ignition coil serves as a high voltage transformer. It steps up the ignition system's primary voltage from 12 volts up to thousands of volts.
The actual firing voltage needed to create a spark across a spark plug's electrode gap depends on the width of the gap, the electrical resistance in the spark plug and plug wires, the air/fuel mixture, the load on the engine and the temperature of the spark plug. The voltage required is constantly changing and can vary from as little as 5,000 volts up to 25,000 volts or more. Some systems can put out as much as 40,000 volts under peak demand.

Ignition coil failures
The ignition coil is very strong and reliable, but it can fail for a variety of reasons.Heat and vibration can damage the winding and insulation of the coil, resulting in short circuit or open circuit in the primary or secondary winding.But the number one killer of ignition coils is voltage overloads caused by faulty spark plugs or spark plug wires.
If the spark plug or spark plug wire is disconnected or the resistance is too high, the output voltage of the ignition coil may rise to the point where the insulation inside the coil is destroyed, resulting in a short circuit.If the output exceeds 35,000 volts, the insulation of many coils may be damaged.Once this happens, the output voltage of the coil may drop while the engine is under load, causing an ignition misfire, or the coil may stop output any voltage, preventing the engine from starting or running.
If the positive terminal of the coil has a battery voltage and is earthed through the ignition module or circuit, but no spark is generated, the coil is faulty and needs to be replaced.
Tip: If the ignition module fails multiple times, it may be due to damage to the ignition coil.An arc or short circuit in the coil can overload and damage the circuitry inside the ignition module.

Ignition coil diagnosis
When a coil failure occurs in the distributor ignition system, it affects all cylinders.Under load, the engine may fail to start or misfire severely.Fires can also jump between cylinders.However, on an engine with a disallocator-less ignition system (DIS) or plug-and-play coil (COP) ignition system, a single coil failure affects only one cylinder (or two cylinders, if it is a DIS waste spark system, the two cylinders firing in opposite order share the same coil).
If your engine is not running properly (firing) and the Check Engine light is on, use a code reader or scan tool to check for misfire code.
On 1996 and newer engines with OBD II and fire detection, coil failures are usually set with the P030X fire code, where "X" is the number of the fire cylinder.For example, the misfire code P0301 will tell you that # 1 cylinder is on fire.But the misfire code can be caused by ignition problems, fuel problems, or compression problems, so don't jump to conclusions because assume that a misfire means a faulty coil, spark plug, or plug wire.It may also be injector damage or compression leakage (valve bending or burning out).
If the coil is short-circuited or disconnected, the coil code on the cylinder can also be set.If no code is available, a digital ohmmeter should be used to measure the primary and secondary resistances of the coil.You should also remove and inspect the spark plugs.Check the spark gap and check the spark plug for deposits to see if the fire was caused by carbon accumulation or oil.Also check the plug wire (if any) to ensure that the resistance of the wire is within the specification.
If the coil, the spark plug and plug line seems to be no problem, may be caused by nozzle dirty or dead fire (please check the resistance of the spray nozzle and power, and use NOID lamp check PCM drive pulse) if injector it looks good, please compress check, to see if there are any more bad cylinder valve or seal leakage.
Note: If an engine with a COP ignition system starts normally but fails to start because there is no spark, the problem is not one or more faulty coils.The fault is most likely a crankshaft or camshaft position sensor failure, a coil supply problem in the ignition circuit, a damaged ignition module (if used), or a faulty ignition coil driver circuit in the PCM.

How to test an ignition coil
Warning: Do not remove the plug wire or the high voltage output wire of the coil to test the spark.In addition to the risk of severe shock, an open plug or coil wire can increase the voltage requirements on the coil to a level that could damage the coil.The only safe way to test for sparks is to use the spark plug tester tool.
If you suspect a problem with the coil, use an ohmmeter to measure the primary and secondary resistances of the coil.If either is out of specification, the coil needs to be replaced.

Another Method for Testing an Ignition Coil
Another way to test the ignition coil is to use a "spark tester."You can find inexpensive spark testers on eBay or most auto parts stores.The in-line spark tester is mounted between the plug coil ignition coil and the spark plug.In case of engine shutdown, disconnect the coil from the spark plug, connect one end of the spark tester to the top of the spark plug, and then connect the other end to the coil output.A spark tester with a long probe must be used for the pen coil mounted on the spark plug and the spark plug tucked deep into the cylinder head.
After installing the spark tester, start the engine.If the light on the spark tester flashes, the coil is generating the ignition voltage and the circuit that controls the coil is working.If the engine is on fire, the spark plug may scale, break or short circuit.No flash means coil damage or coil control circuit damage.Check whether the coil connector is loose or corroded.Poor wiring may prevent good coil ignition.

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