Updated on 19 October, 2021
Spark plugs are usually found at the centre of a cylinder head of light-weight engines. Cylinder heads like these are typically one of the biggest components of a light-weight internal combustion engine. A thin, flexible wire and matching fitting shoved past the end of an ignited spark plug gives the electrical energy required to create the isolated spark plug tip. The tip is responsible for igniting the fuel/lighter fluid that is contained within the spark plug. This is the way a spark is initiated in an electric engine. When the spark plug tip does not ignite the fuel/lighter fluid in the plug is forced to flow past a valve that shuts off the supply of electricity.
The spark plug tester lets you see whether the spark plug has in-let or out-let. The in-let spark plug is connected to the combustion chamber by a thin flexible copper wire. The in-let part of a cylinder head is adjacent to the spark plug and is identified by the white part just below the piston rod.
There is another type of spark plugs - the out-let spark plugs. These are generally larger than in-let spark plugs. They are positioned inside a combustion chamber that is constructed like a soda bottle - hence the term soda-in or soda-out ignition system. The steel threads that connect the thin threads to the steel cylinder head and the screw drive that holds the assembly together are visible in the exhaust port.
To use a spark plug tester, first place the ignition wire in the seat just in front of you. Near the firewall, there is usually a black lever that can be pulled upward. You will need to look to see if the ignition switch is engaged. If it is not, then pull the lever to the left (ascending) and push it out towards the driver. Pulling the lever farther right will disengage the switch.
Next, pull out the spark plug tester plug and blow the tester. If the engine does not light, then the tester is either worn or the spark plugs have died. Reinstall the ignition system. A worn spark plug will rotate at high speeds and produce very little electricity. This means that one of two things is true: the tester is showing excess wear on the threads are rotten.
If the spark plugs are rotten, then they will either be missing, broken off or otherwise bent upon themselves while the ignition wire was still attached. This can also occur if the ignition wire has come loose through static or other reasons. Once you have taken both of these items off, you can inspect the rest of your device to see what kind of damage exists. The signs that a plug may be bent are very obvious. Look for:
The most common signs of worn spark plugs are: terminals not properly attached to the wires - especially between the firewall box and the motor, or the wires to the spark tester are crossed. You can also test your lights by removing the headlights and testing the connections using a flame-fueled tester that has been cut in half. Again, keep in mind that the wires to the spark tester must cross the firewall box to attach to the battery and they must be securely tapered or bent on each end. These tests are usually performed on new installations and will not apply to installations made prior to the aforementioned date.
Another sign of wear is if the terminals are bent - but, again, this will not be seen if the ignition is still on the vehicle. One final sign of wear that may be difficult to see is if the spark plugs themselves get hot while the vehicle is being used. You can test this by slowly cranking the ignition up and down. If the engine sounds "hot" when cranking up and "cold" when cranking down, the new plugs may be too hot to be effective. You should replace them with a different size and/or age plug.