How to Test a Spark Plug with a Multimeter (Complete Guide)
Content
Whenever we talk about vehicles and engines in regards to maintenance, we always hear about the spark plug first. It is an integral part of the engine, present in all types of gas engines. Its main job is to ignite the air-fuel mixture inside the engine at the right times. Poor fuel quality and use can contribute to spark plug failure. Higher fuel consumption and less power than usual are signs of a bad spark plug. It's good to check your spark plug before big trips and it's part of your annual maintenance routine.
The spark plug can be tested with a multimeter, in which you can use the ground test. During the ground test, the fuel supply to the engine is turned off and the spark plug wire or coil pack is removed. You can remove the spark plug from the cylinder head. When checking with a multimeter: 1. Set the multimeter to the value in ohms, 2. Check the resistance between the probes, 3. Check the plugs, 4. Check the readings.
Not enough details? Don't worry, we'll take a closer look at testing spark plugs with a ground test and a multimeter test.
Ground test
First, a ground test is performed to test the spark plug. You can follow these steps:
- Shut off the fuel supply to the engine
- Remove the spark plug wire and coil pack.
- Remove the spark plug from the cylinder head
1. Shut off the fuel supply to the engine.
For vehicles with fuel injection, you should simply pull the fuel pump fuse. Disconnect the fitting from the fuel pump on carbureted engines. Run the engine until all the fuel in the system has burned out. (1)
2. Remove spark plug wire or coil.
Loosen the mounting bolt and pull the coil out of the fork, especially for vehicles with coil packs. If you have an older engine, disconnect the wire from the spark plug. You can use spark plug pliers to make this process easier.
3. Remove the spark plug from the cylinder head.
Remove the spark plug from the engine cylinder head to test it with a multimeter.
You can check out more here for ground testing.
Multimeter test
Follow the steps above and use a multimeter to test the spark plug. Follow the steps given below:
- Set the multimeter to ohms
- Check the resistance between the probes
- Check forks
- Look around reading
1. Set the multimeter to ohms
The ohm is a unit of measure for resistance and other related calculations. You should set your multimeter to ohms to test the spark plug for best results.
2. Check resistance between probes
Check the resistance between the probes and make sure there is no resistance in them. This is necessary to obtain accurate readings.
3. Check the plugs
You can test plugs by touching one wire to the contact end of the plug and the other to the center electrode.
4. Check reading
Check the readings to make sure that the resistances specified in the specifications are consistent. Readings in the range of 4,000 to 8,000 ohms are acceptable and also depend on manufacturer's specifications.
Spark Plug Operation
- Spark plugs can be seen on top of the cylinder head in almost all kinds of small engines. They have cylinders and cooling fins on the outside and are considered the largest part of small gasoline engines.
- A thick wire and a fitting put on the end of the spark plug can supply electricity.
- The engine has an ignition system that can send a very high voltage pulse of current through this wire. It can move further to the spark plug and typically has 20,000-30,000 volts for a small engine.
- The tip of the spark plug is located inside the combustion chamber of the engine in the cylinder head and holds a small gap.
- It jumps into mid-air when high-voltage electricity hits this gap. The circuit ends with inflow into the engine block. This surge results in a visible spark that ignites the air or fuel mixture inside the engine to run it. (2)
- All kinds of problems with spark plugs come down to a few flaws that can prevent electricity from getting into the critical gaps of the spark plugs.
Elements required for checking spark plugs
Only a few tools are required to check spark plugs. There are many professional ways to do this, but here we will mention some of the most important tools to get you ahead.
Tools
- Resistance multimeter
- spark plug socket
- Spark plug wire puller for older vehicles without coil packs
Spare parts
- Spark plug
- Car sockets with coil packs
Safety when testing spark plugs
We recommend that you follow some safety precautions when checking spark plugs. All you need is a multimeter along with an open plug under the hood.
Follow these guidelines:
- Put on a set of goggles and gloves.
- Do not pull spark plugs when the engine is hot. Let the engine cool down first.
- Make sure engine cranking is complete and there are no moving parts. Be attentive to all kinds of moving parts.
- Do not touch the spark plug with the ignition on. On average, about 20,000 volts pass through a spark plug, which is enough to kill you.
Summing up
Evaluating spark plugs and spark plug wires is just as important as checking any other engine component, especially in vehicles before a long trip. Nobody likes to be stranded in the middle of nowhere. Make sure you follow our guide and you'll be clean.
You can check out other multimeter guides below;
- How to check the car ground wire with a multimeter
- How to test a circuit breaker with a multimeter
- How to use a multimeter to check the voltage of live wires
Recommendations
(1) fuel supply - https://www.sciencedirect.com/topics/engineering/fuel-supply
(2) electricity - https://www.britannica.com/science/electricity
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