Ford AGSF-42F-MX
Spark Plug

A bridged gap inspection should be performed on the spark plug alongside the examination of deposit build-up between electrodes which can result from oil or carbon faults. Clean the spark plug in case of necessity. Examine the insulator shell bore electrodes for black wet oil deposits as a sign of fouling which indicates ring or piston wear and improper bearing looseness along with excessive valve-to-guide clearance all require repair before installing a new plate. A spark plug needs cleaning if black dry fluffy carbon deposits appear on insulator tips, exposed shell surfaces, and electrodes because they typically develop from incorrect heat ranges, uncleaned air filters, fuel mixtures becoming too rich or from excessive engine idling. Normal burning appears as lightly colored gray or tan residues on the spark plug firing tip. The presence of melted electrodes along with damaged insulator and metallic deposits points to engine damage possibly caused by incorrect ignition timing lapses or delivering wrong fuel types or non-professional heli-coil insert installation into spark plug threads so a new spark plug becomes necessary. Whiteness or light gray coloration with bluish-burnt electrodes exists due to engine overheating or incorrect fuel usage and loose spark plugs or improper heat-ranging spark plugs or insufficient fuel pressure or wrong ignition timing that demands replacing the spark plug. The spark plug should be cleaned if there are fused deposits which look like bubbles or blisters found during the inspection.

An inspection of the spark plug must focus on visible gap bridging because oil and carbon fouling can create ceramic insulation blockage. Clean the spark plug unless it shows no need for cleaning. A new spark plug installation should only proceed after fixing any oil leak issues and dealing with worn rings and pistons as well as excessive valve-to-guide clearance and worn or loose bearings because excessive oil entering the combustion chamber causes wet black deposits on the insulator shell bore electrodes. Particle fouling is detectable by inspecting black fluffy carbon buildup on insulator tips and shell surfaces and electrodes along with testing the heat range of the plug with air filter state and fuel mixtures and duration of engine operation. Normal operation of the firing tip means it will accumulate light tan or gray materials. Witnesses to pre-ignition can be identified through electrode melting and damaged insulator appearance together with metal residue indicating potential engine damage from improper ignition timing or improper fuel type use or unapproved heli-coil insertion instead of spark plug threads so a new spark plug needs replacement. The combination of engine overheating and wrong fuel type along with loose spark plugs or heat range mismatched plugs or low fuel pressure or improper ignition timing leads to petechial spots and bluish-burnt electrodes. If overheating is observed it requires immediate replacement of the spark plug. The inspection for fused deposits which form as bubbles or blisters following sudden acceleration should prompt cleaning of the spark plug in case of detection.