Plain English Meaning

It is when gunk builds up on a spark plug so it cannot spark properly. This usually happens when the engine runs too cool for too long, often during low-power descents.

Full Definition

A condition in which deposits of lead, carbon, oil, or other combustion residue accumulate on the firing end of a spark plug, reducing or preventing its ability to produce a strong spark. Fouling commonly occurs during prolonged low-power operations, extended idling, or descents at low engine RPM with a rich mixture, where combustion temperatures stay too low to burn off these deposits.

Context Anchor

Seen in engine operation discussions, especially during long low-power descents such as a steep spiral, extended , or other periods when the engine may cooler than .