Diagnosis of Spark Plug - TORCH SPARK PLUG

Terminal Nut Loose

Appearance	Analysis	Improvement
Terminal nut loose	The connection terminal is occasionally loose in the running.	Increase the torque to tighten the terminals.

Flash over

Appearance

Analysis

Improvement

Flashover

● Longterm use of spark plug;

● Poor insulation performance and aging of ignition cable shell high-voltage wire sheath insulation performance is poor, aging;

● Oversize gap between the ignition cable and the ceramic piece.

Solution: Replace the spark plug and ignition cable shell in that cylinder if there is a flasover occures.

Improvement: Add insulating grease to the ignition cable shell.

Cracked Insulator

Appearance

Analysis

Improvement

Cracked Insulator

● Socket slip, worn or incorrect size socket

● Mishandled

Choose the correct socket

Improper Tighten of Gasket

Appearance	Analysis	Improvement
Improper Tighten of Gasket	Improper torque force and swivel angle.	It is recommended to use a professional wrench according to the instructions for installation.

Metal shell rust

Appearance	Analysis	Improvement
Metal Shell Rust	Due to poor water resistance of the spark plug cap, when water penetrates the place where the spark plug is installed, the main metal will rust.	There is no deterioration to the function of spark plug. But it may cause a misfire if water penetrates into spark plug cap.

Oil Fouled/MMT Fouled

Appearance	Analysis	Improvement
Oil Fouled	Mainly because of the wearing and damage pf piston and cylinder. Or because of the over density gas by incorrect adjust of carburetor	Change a lower heat range spark plug.
MMT Fouled	MMT is deposited to the ignition end to form a dark brown substance, 700-800 degrees MMT melts and conducts electricity, the spark plug insulator resistance decreases, and misfire! Misfire occurs when the vehicle is at high speed and heavy load, and the speed drops. Radiated discharge traces can be seen at the ignition end of the spark plug.	Change the gasoline and spark plug

Broken Thread

Appearance

Analysis

Improvement

Remark

Breakage of the thread

● The fracture plastic of the breakage deformation, indicating that it is an overloaded tough fracture;
● The thickness of the outer sealing gasket is extremely bad, indicating that the installation torque of the spark plug is too large.

Others reasons cause thread breakage

● Outer gasket material

● The eccentricity or thin wall of the undercut may cause the poor strength of the shell, which causes breakage under torque installation.

Appearance

Analysis

Remark

Breakage of the thread

● The fracture plastic of the breakage deformation, indicating that it is an overloaded tough fracture;
● The thickness of the outer sealing gasket is extremely bad, indicating that the installation torque of the spark plug is too large.

Others reasons cause thread breakage

● Outer gasket material

● The eccentricity or thin wall of the undercut may cause the poor strength of the shell, which causes breakage under torque installation.

Carbon Fouled / Electrode Melten

Appearance	Analysis	Improvement	Remark
Heat range mismatches	When the skirt of a insulator is short, the heat dissipation is fast and the combustion is insufficient, carbon fouling is easy to occur.	Choose the spark plug with correct heat range according to original engine specifications	As mentioned the optimal operating temperature range for a spark plug is 450 – 870°C, 450°C is the spark plug self cleaning temperature at which point carbon deposits will burn off. So the heat range of a spark plug should meet its self cleaning temperature.
Carbon fouling during the running of engine	● Lower engine rotating speed is easier to lead carbon fouling. ● Carbon deposit occurs while an over-rich of fuel mixture caused incomplete combustion. ● Poor quality gasoline leads to incomplete combustion of the engine, thus carbon deposits on the firing end. ● The oil vapor is not well filtered while the engine cylinder cover is unreasonably designed. Oil fouling at the inlet of the throttle body or the intake manifold which causes carbon deposits on firing end. ● Bad driving habits like full load condition, poor road condition, rapidly speeding-up or panic stop etc cause carbon deposits as well.	Get the carbon deposits cleaned while vehicle travel accumulates 3000 to 5000 kilometers usually.	Carbon fouled occurs often in cold weather.
Premature ignition	● Gas leakage: The deformation of the outer seal is not enough, which causes the seal of the spark plug to be damaged, and a serious air leak, which increases the temperature in the cylinder. If the metal shell continues to overheat the plug temperature may rise and abnormal combustion may result.Thus a early misfiring which causes firing end melt. ● No gas leakage: After the pre-ignition occurred, the ground electrodes melted abnormally at high temperature. Under the repeated washing of the air pressure, the melt splashed around and dripped on the ceramic body, causing the small head to bubble and shell.
Other causes for spark plug melten	● Neither the center electrode nor ground electrode has poor heat dissipation. ● The engine cooling system goes wrong.

Spark plug diagnosis