How To Test Your Vehicle’s Ignition Coil?

Whenever you are testing or checking ignition coils, wear thick rubber gloves during full-time contact with any of the vehicle power-exposure sources. These gloves will shield your hands from harmful chemicals found in automobile engines and batteries. Also, switch off your engine when checking or testing ignition coils because an engine running while checking or testing can cause an electric shock from the ignition system.

The electrical resistance of the ignition coils is different for each individual vehicle.  Check what the correct resistance reading of the ignition coils should be for your vehicle. These specifications can usually be found in your vehicle’s manual and are usually specified as a range, and are measured in “ohms” (symbol: Ω).

You should start the test with the vehicle in park and the engine turned off. To find the ignition coil, open the hood. Though its precise location varies from vehicle to vehicle, it is usually located near the fender or bolted to a bracket near the distributor. It is important to note that in vehicles without a distributor, the spark plugs are connected directly to the ignition coil.

You'll need to unplug the ignition coil from the distributor wire before using a wrench to unscrew it from its mounting. Before starting this procedure, make sure your car is off and has had time to cool.

An ignition coil has 3 electrodes + 2 poles on the sides and 1 pole in the middle (center contact). Switch on your multimeter and touch each multimeter’s measuring tip to the two outer electrodes. You’ll get the primary winding resistance value on the multimeter. Write down the resistance value of the primary winding. The primary resistance of most ignition coils should fall between 0.4 and 2 ohms, check your manufacturer's specifications in the vehicle repair manual for the precise value. If the reading is zero, the primary windings have internally shorted and the ignition coil needs to be replaced.

Touch the measuring tips of the multimeter to one of the two electrodes and touch the other to the center contact, (where the main high-voltage wire connects to the distributor). You’ll get the secondary winding resistance value on the multimeter. The secondary resistance of most ignition coils should fall between 6,000 and 10,000 ohms; however, the precise range should be found in the manufacturer's specifications. An excessive reading indicates that the ignition coil is open and needs to be replaced, while a reading of zero indicates that the ignition coil has short-circuited and needs to be replaced.

If your vehicle has more than one ignition coil, follow Steps 4 and 5 to test each one separately. Verify that each ignition coil is functioning properly.

After testing each ignition coil, replace any defective ignition coil and reinstall the remaining ignition coils in the car. Reconnect all electrical connections and replace any engine covers or other trim pieces that have been removed.

The test should begin with the engine off and the car in park. Open the hood and look for the ignition coil. Although the exact location varies from vehicle to vehicle, it is typically bolted to a bracket near the distributor or situated close to the fender. It's important to remember that spark plugs in cars without distributors are connected directly to the ignition coil. Finding the distributor and then following the wire that isn't connected to any spark plugs is a good method for finding the ignition coil. Make sure you have access to insulated tools (especially pliers) to prevent electric shock and that you are wearing safety goggles or other eye protection before starting the test.

Remove the spark plug wires from the spark plug itself. These spark plug wires run from the distributor cap to each of the sparks plugs individually. Always use gloves and insulated tools while working with the vehicle’s electrical system to prevent any injury. 

To prevent potential damage and save time to your spark plug while removing the spark plug,  consider using a spark plug tester.

• Place the spark plug tester on the wire in place of reattaching the spark plug to it.

• Ground with the automotive clip. 

• Next, go ahead and have your friend start the car while you keep an eye out for sparks in the spark plug tester's gap. You can avoid contaminating your combustion chamber by using a spark plug tester.

Once you have removed the spark plug wire, remove the spark plug with a specialized socket wrench called a spark plug socket. From now on, take care not to let anything fall into the empty hole left by your spark plug. Leaving debris in this hole can cause engine damage as the vehicle runs. To prevent debris from entering the combustion chamber, cover the hole with a clean rag or towel.

Reattach the spark plug to its wire carefully. Your spark plug should still be attached to the distributor but not seated in its "hole." Use insulated pliers to handle the spark plug to reduce the risk of electric shock.

Position your spark plug (with the wire still attached) such that the threaded "head" of the spark plug touches some metal part of the engine. This can be any strong metal part of the engine block, including the engine itself. Use insulated pliers to carefully hold the spark plug (and, if possible, gloves). Don't put yourself at risk of electric shock in the following steps by skipping this simple precaution.

Before starting the engine to test the spark plug, disable the fuel pump. The engine will not start after this, allowing you to check the ignition coil for a spark. If you do not remove the fuel pump relay from the fuel pump, the engine cylinder which is going to be tested by you will not fire because there will be no spark plug. But still be flooded with fuel,  which could damage engine parts and engine cylinders.

Get a friend or someone to start the car. The electrical system of your vehicle and the spark plug you're holding will be powered by this (assuming your ignition coil is working).

When the engine cranks and you see a bright blue spark jump across the spark plug gap, this means that your vehicle’s ignition coil is working properly. If you don't notice a blue spark, your ignition coil is malfunctioning and needs to be replaced. If you see an orange color spark, this means that the ignition coil is supplying insufficient electricity to the spark plug and needs to be replaced. Finally, if you do not see any spark, this means that the ignition coil is “dead”, or there are one or more faulty electrical connections, or that you've done something wrong in your test.

After finishing your test, make sure the engine is off before essentially going through the previous preparation steps in reverse order. Reconnect the high-voltage spark plug wire after removing the spark plug, inserting it back into the corresponding spark plug hole. To avoid incorrect wiring orders, label or add specific marks to the ignition coil and connect it to the correct spark plug wire.