Having trouble starting your vehicle is one of the main signs of a bad spark plug. Listen for rattling, sputtering, or metallic pings that signal when a spark plug is making your engine misfire. Check if your gas mileage has gotten worse since a bad spark plug won't burn fuel as efficiently.
Verify Lack of Spark
To do so, you want to check to see if the spark plug itself is firing. With a misfire, start with the cylinder in question. With a no run, pick any plug you see fit. Next, test with either a spark plug test light or connect the plug to the ground and turn the key.
Malfunctioning spark plugs cause engine problems including, misfires, hard starts, reduced gas mileage, rough idling, and lack of acceleration. Driving with a faulty spark plug will be difficult because the engine might fail to function.
A red or yellow spark is weak and probably will not spark in the cylinder. A blue or white spark is strong and has enough voltage to fight across the spark plug gap even under pressure within the cylinder.
For an engine to start and run properly, the energy must arc the plug and keep that arc going until all of the combustible mixture is consumed. Anything less and the engine will be weak, run rough, stall, and misfire.
If you have a weak spark, you may be dealing with a: bad spark plug wire. bad distributor cap or rotor. faulty ignition wire or coil.
The least likely cause of a weak spark is a battery voltage of 12.2 Volts. Even though the battery voltage is less than normal, it should be enough to allow the ignition coil (s) to become fully saturated and provide the correct spark to the spark plugs.
It's important to remember that many times when a coil fails, it becomes weak. It still produces spark, and may still run the vehicle fine at times, but often under load, or acceleration, it can produce a misfire. Other times, the coil completely fails and stops working altogether.
Ordinary copper and nickel spark plugs should be changed every 30,000 to 50,000 miles, unless otherwise suggested by the spark plug manufacturer. Platinum and iridium spark plugs tend to last longer than standard copper and nickel spark plugs. Expect to change them every 60,000 to 150,000 miles unless otherwise noted.
If you let your spark plugs go for too long, you could do some severe damage to your engine. The deposits that build upon the plugs can eventually cause them to misfire. When this happens, the unburned fuel in the cylinders can start to eat away at the cylinder walls.
If your Spark Plugs are failing your engine will sound rough and jittery when running at idle. This can cause vibrations to resonate through the vehicle which could cause further costly damage.
Test with a spark plug tester
Start the engine, or simply turn it over if it won't start, and watch the transparent sides of the tester. If no visible spark or glow is present, then you can be sure that no spark is occurring at the all-important tip of the spark plug.
If no spark is visible, check to see if the points or wires are shorting to ground either at the points or at the primary terminal screw going through the housing. Also check where the contact spring connects to the main frame of the points and make sure the insulator is not melted.
Most DIS no start problems are caused by a bad crank position sensor. Many DIS systems use the "waste spark" setup where one coil fires a pair of spark plugs that are opposite one another in the firing order. Others, including the newer coil-over-plug systems, have a separate coil for each spark plug.
Keep your ears open for any rattling, pinging or knocking sounds—these are another bad spark plug symptom. If your vehicle's engine is making any unusual sounds or vibrations while idling, your vehicle's spark plugs may not be functioning properly to keep the engine running smooth.
Your Auto Has the Wrong Spark Plugs or Spark Plug Gap
Using any spark plugs other than those the manufacturer recommended, you risk having a knocking engine. Also, if your spark plug gap is too close, your spark will be too weak. A gap too broad could keep it from sparking or cause a misfire.