Question

the new spark plug shown in the photograph has been fouled. which of the following is the most likely cause?
a) retarded ignition timing
b) short - term fuel trim
c) stuck open injector
d) defective spark plug

Explanation:

A stuck - open injector will continuously supply fuel to the cylinder. This excess fuel will not be fully burned, and the unburned fuel and its by - products will foul the spark plug. Retarded ignition timing (Option A) mainly affects combustion efficiency in terms of timing but is less likely to cause such a rapid fouling of a new spark plug. Short - term fuel trim (Option B) is a temporary adjustment and not likely to cause fouling. A defective spark plug (Option D) would have issues from the start, but the problem states it's a new spark plug, so fouling from excess fuel due to a stuck - open injector is more likely.

Answer:

C) Stuck open injector