When this happens, the end of the spark plug will have wet oily or greasy looking gunk over the electrodes, and it will also smell of oil. Engine oil leakĪn oil leak in the combustion chambers of the engine can cause the spark plugs to foul up in Sierra 1500. Using spark plugs with too cold heat range can also cause carbon fouling, in this case the firing end does not reach the self-cleaning temperature of approximately 450☌ (842☏). For example, a malfunctioning MAF sensor or O2 sensor can cause the engine to misfire or run rich that can cause carbon fouling of the spark plugs.Ĭommon causes of engine running rich in GMC Sierra 1500 are defective or dirty MAF sensor, bad upstream O2 sensor, malfunctioning fuel pressure regulator, leaky injector and faulty engine coolant temperature sensor.Ĭarbon fouling of the spark plugs can also be caused by continuous low-speed driving and/or short trips, over-retarded ignition timing (plug ignites the fuel too late) or due to bad ignition coils/wires. Your Sierra 1500 may not start if the spark plugs have worn too much, or if they have been contaminated due to improper combustion. The ignition system in your Sierra 1500 will have to work a lot harder to be able to ignite the air/fuel mixture in the combustion chambers.

When the spark plugs go bad, it is going to take longer for the engine to turn over and start.

If your vehicle is getting significantly lower gas mileage than usual, its time to inspect the condition of the spark plugs. Poor fuel mileageĮxcessive fuel consumption is a common sign of bad spark plugs in Sierra 1500. The engine will not run smooth when idling, you may also feel vibrations in the cabin. Rough idleĪnother indication of bad spark plugs in GMC Sierra 1500 is rough idle. When you press the gas pedal in your Sierra 1500, the vehicle may hesitate to accelerate and it will take longer to reach your desired speed. If the spark plugs are not generating sparks properly, the engine will lose power. In case of doubt, check the condition of the spark plugs and replace them if found defective. However, it can happen that there are no error codes. If you see any error code from P0300 to P0312, it indicates that there are misfires in the engine. To perform further diagnostics, you will need to connect OBD2 scanner to your vehicle.

When one or more of the spark plugs start to fail or has failed in your Sierra 1500, it will cause the engine to misfire and the check engine light may illuminate in the instrument cluster. Symptoms Check engine light illuminates due to misfires

350z bad spark plug symptoms