How to Test an Engine Ignition System Video

The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil and that transfers the electrical energy into the secondary ignition system, i.e. coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug. This system is triggered by the primary ignition system, this system varies depending on manufacturer but all operate on the same principle, use some kind of low voltage trigger system i.e. crankshaft position sensor (CKP), camshaft position sensor (CAS). 

This low voltage system (1.5 to 3.0 volts) is amplified to 12 volts by using an ignition module (amplifier) and then transferred to the primary side of the ignition coil. The PCM (powertrain control module) controls the engine ignition timing by advancing and retarding the primary trigger signal. In older cars a points, condenser and a vacuum advance unit performed this job. We have listed the most popular causes for an ignition system to fail or misfire.

Ignition Testing Procedure

Step 1 - Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, air bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If all fuses test ok continue to the next step.

Step 2 - To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, air bag) and the fuses test ok a trouble code scan is needed to identify any system trouble. Use a simple scanner tool to retrieve trouble codes and check if they relate to the specific problem, like an ignition coil failure code. If a trouble code is present but does not pertain to the immediate problem like an EVAP code, ignore it until a later time, after the engine is running properly. The reason we repair non-related codes after the engine is running properly is because sometime false codes can be triggered by a rough running engine. Once the engine is running properly the code present might cycle and turn itself off. 

You might say "if the engine isn't running right shouldn't it have a check engine light and a trouble code? "Sometimes conditions occur that will not be detected by the computer, example: if the intake or exhaust valve operation fails the computer cannot detect the failure because the problem is not sensor related, so the engine doesn't run smooth and the computer thinks everything is ok with no codes. If the trouble code retrieved relates to a cylinder misfire like an injector driver or ignition coil failure first these problems and re-test system. If no trouble codes are present proceed to the next step.

Step 3 - Check the ignition system basic output voltage, this will test the ignition system by observing the spark from the ignition coil. This is done using a test light and inserting the sharp probe into the end of the plug wire boot allowing a sizable gap from the inside plug wire terminal and the test light probe. If the engine does not run and you are testing the ignition system output continue with this test. If you are testing the ignition system to troubleshoot an engine cylinder misfire you will need to disconnect the fuel pump fuse or control relay and bleed off fuel system pressure to stop the engine from starting. (note: sometimes the engine will run slightly until excess fuel is burned) To locate the fuse or relay for the fuel pump located in the fuse box or power distribution center, if you cannot locate the fuse or relay consult your cars owner's manual or an online repair manual for their locations.

Step 4 - In this step remove the plug wire or ignition coil wire to gain access to the end of the plug wire, coil wire or coil over spark plug boot depending on a particular ignition system configuration. Ground the test light lead to a known ground source like the negative battery terminal, insert the probe end of the test light into the end of the boot creating about a 3/4 inch gap between the probe and the terminal inside the boot. Position the boot and test light combination for clear observation and away from rotation accessories. While observing the boot/test light probe gap have a helper crank the engine over (keep hands and clothing away from rotating accessories). 

There should be a bright blue electrical spark between the spark plug/coil wire/coil terminal and the test light probe. If your are testing the system for a cylinder misfire continue this test for the remaining cylinders, look for good spark quality if there is no spark present on a particular cylinder inspect the plug wire, cap and rotor or individual ignition coil if corrosion is present on any part of the terminals or wires replace the component and re-test. If the coil has no electrical discharge output continue to Step 6, if electrical discharge is present at the coil wire and not the plug wires continue to Step 5

Step 5 - If your car is designed with a distributor that has a cap and rotor remove the distributor cap and inspect the rotor. The ignition rotor transfers high voltage to the plug wires and then the spark plugs and can short circuit to the distributor main shaft causing the spark to enter the distributor but not exit. Remove the ignition rotor and check for burn or ash marks on the underside of the rotor. Also inspect the coil wire and distributor cap terminals for corrosion, look for any burn or ash marks on the wire or terminals. Replace any damaged, burned or corrected components with new or quality used parts and retest system.

Step 6 - This next test will tell us if the primary ignition system is supplying an electrical trigger pulse to the ignition coil. To test the ignition trigger pulse remove the small wires from the coil. Using a voltage multi-meter connect the leads to both wires and set the multi meter to DC voltage. Next have a helper crank engine over and observe the voltmeter, if the meter jumps from 12 volts and then to zero in rapid succession the trigger system is working properly. Next check the ignition coil for corrosion if no corrosion exists use the voltage multimeter to test the coil primary and secondary circuits for continuity and resistance. This testing procedure will work for most automotive coils. 

With all wires disconnected from the coil, use a multi-meter switched to ohms and check the resistance between the small side terminals of the coil. You should get a reading of 0.75 to 0.81 ohms of resistance. Then check the resistance between on either side terminal and the center high output terminal. The ohms reading should be about 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate the coil is shorted and needs to be replaced. If there is no primary ignition trigger output proceed to next step.