Methods for diagnosing spark plug faults

Methods for diagnosing spark plug faults

(1) Instrument inspection: 

The spark plug with a slight magnetic crack and a firing failure only occurring under heavy load is installed on the spark plug tester. Compressing air to 748 KPa is injected into the tester to simulate the working condition of the combustion chamber during the compression stroke. High voltage electricity is applied to the spark plug to create a spark between its electrodes (which can be observed through the glass window). A continuous and bright spark indicates a good spark plug; otherwise, there is a fault. 

(2) Touching Method: 

Shortly after the engine is started, you can directly touch the spark plug housing with your hand to check its temperature for diagnosis. If the temperature is high, it indicates normal operation; otherwise, there is a fault. The surface temperature of the heated engine porcelain body is very high. Do not touch it with your hand. Keep the engine running at idle speed and use your thumb and index finger to touch each cylinder high-voltage lead for several seconds in sequence. Based on the feeling, determine which cylinder's spark plug has a fault. The high-voltage lead in normal operation feels pulsating when touched with your hand. The faulty high-voltage lead feels no pulsation or has intermittent pulsation. After determining that a certain cylinder is not working properly, further inspection is required. If there are no other reasons, it is the spark plug that has the fault. 

(3) Ignition Cut-off Test Method: 

Make the engine run at idle speed. Use a screwdriver to cut off the spark plug (ground connection). If the spark plug that has been disconnected is faulty, the engine's operation will remain unchanged (the engine's own faults need to be ruled out). If the engine shakes immediately after the spark plug is disconnected, it indicates that the cylinder is working properly. 

(4) Comparative Experiment: 

Use the spark plugs from the cylinders that performed well in the fire-off test, and swap them with the spark plugs from the cylinders that performed poorly in the test. Conduct a comparative test to further determine the quality of the spark plugs. 

(5) Spark Test: 

Remove the faulty spark plugs and place them flat on the engine cylinder block. Disconnect the high-voltage bus distributor end and connect it to the spark plug terminal. Turn on the ignition switch and move the distributor bimetal. Make the high voltage electricity jump between the spark plug electrodes. If the spark is continuous and bright, the spark plug is fine; otherwise, the spark plug should be replaced. 

(6) Observation and Identification: 

Remove the spark plugs and observe the color of their electrodes. Spark plugs with white or rust-colored electrodes are functioning properly; those with black smoke on the surface (except when the mixture is too rich) have a poorer working quality; and those with severe carbon deposits or oil stains have the poorest working quality or cannot work at all.

Whether the spark plugs are functioning properly has a significant impact on the power and economy of the vehicle. Therefore, drivers should be able to diagnose and troubleshoot spark plug failures. One method: Shortly after starting the engine, if you notice a "cylinder shortage" phenomenon, you can use the "touch" method to determine whether each cylinder is working properly. The method is to turn off the engine, then touch the insulating porcelain body of each cylinder one by one with your hand. The one with a lower temperature indicates that the cylinder is not working properly. Two methods: Use a screwdriver to short-circuit the spark plug (or remove the high-voltage wire of the individual cylinder) for a fire-off test. If there is no significant change in the engine's operation, it indicates that the spark plug of that cylinder is not working properly. Three methods: Unscrew the spark plug and observe. The center electrode is gray-white and functioning properly; if it does not work or is not working properly, the two electrodes of the spark plug will be soaked with oil deposits or blackened due to carbon deposits. Four methods: Place the removed spark plug on the engine cover, then contact the upper part of the spark plug with the high-voltage center wire. Use a screwdriver to move the moving contacts of the distributor, and see if the two electrodes of the spark plug spark. If the two electrodes are soaked or have carbon deposits, the spark will be weak or even no spark; if the porcelain body leaks electricity, it may sometimes leak and spark between the porcelain body and the engine cover. 

Check whether the spark plugs are functioning properly. 

A normal spark plug should have a clean surface and its color should be brown, yellow or yellowish-white. 

(2) If the surface of the spark plug is black, it indicates the presence of carbon deposits or oil stains. This could be due to an overly rich mixture of oil and gas, a faulty power supply system, dirty air filter, or incorrect spark plug heat value usage, etc. Cleaning or replacement is necessary.

3) If there are abraded spots on the surface of the spark plug, and the color is white-gray, it indicates a problem.