The ignition doesn’t
trigger at the right time (a timing issue)
Something is preventing the spark
from having a full charge (a resistance or failure of the system).
In a
modern engine, the computer can sense ignition problems. It uses oxygen sensors to evaluate the air-fuel
ratio
of the engine output. Some engines also have a sensor to detect if the engine is firing too soon (anti-knock
sensor), and to tell if the engine is misfiring by checking the motion of the crankshaft.
TIMING ISSUES
Timing issues occur when the spark plug is firing too soon or too late. Modern engines use the computer to
trigger the timing based on the sensors checking the crankshaft and camshaft. If the timing in a new engine
gets out of sync, it is usually due to the belt or chain wearing out or slipping. A dirty or failing crankshaft
or camshaft sensor can also cause timing issues.
SPARK PROBLEMS OR FAILURE
If the spark plugs don’t get a full charge of electricity, they may not trigger a spark big enough to get a good
burn of the fuel, or they may not fire at all. The spark plug needs to make a good, clean electrical
connection from the coil, through the wire (if used), and ground to the cylinder head. There are lots of
things that can prevent a proper spark from occurring.
Arcing Worn spark plug wires or signal wires can cause “arcing,” which is when the electricity used to fire the
spark plugs is dissipated through an arc point. The spark plugs are carrying tens of thousands of volts and
it
is not hard for a small rub on a wire to cause a voltage arc. An arc, or short, can also ignite fumes
outside the engine, so they can be dangerous. If you suspect a faulty wire, look for points where it may
be touching the engine, or look for cuts or blackened outer areas where it might be arcing.
Ignition Coils Not Firing The ignition coils generate the voltage that triggers the spark plugs. The number of
coils your car has may determine the severity of your problem. If a single coil fails, the engine stops
running. A coil pack may have one or all of its coils fail, and coil-on-plug only affects one spark plug.
Grounding Problems If the spark plug is not making a good connection to the cylinder head, it can’t complete
the circuit, and won’t fire. If any part of the system loses its connection to the ground, the plugs won’t fire.
Ground issues can be maddening to locate and fix.
Contamination There are a lot of things that can contaminate the spark plug and prevent it from firing: oil
from an engine that is seeping into the cylinder, coolant entering the cylinder, deposits from poor gas, or
poor combustion. Any foreign material that gets between the two points on the plug can keep it from
firing normally. Keeping your engine maintained properly will prevent most problems.
Worn Plugs Spark plugs will wear down under normal use. The two points that create the spark will slowly
move away from each other, and the “gap” will increase, making it harder to create the proper spark. A
plug that is damaged will not create a proper spark.
Spark plugs are designed to operate in a specific heat range, and engines are designed to use a specific
plug. In general, you shouldn’t need to change heat ranges on your plugs.
