Which of the following is NOT a cause of engine pinging or detonation?

Pinging or detonation occurs in an engine when the air-fuel mixture ignites prematurely, leading to a knocking sound. This can be caused by several factors, but improper fueling is not a primary cause.

When we consider improper fueling, we're typically referring to using fuel with the wrong octane rating for the engine. However, an octane rating that is too low can lead to engine knocking. Nonetheless, this scenario views improper fueling more as a factor that can influence engine performance rather than a direct cause of engine pinging.

In contrast, the other options directly relate to engine design and characteristics that can create conditions for detonation. An incorrect camshaft can change the timing and dynamics of the engine's operation, leading to issues with combustion timing. A partially clogged EGR (Exhaust Gas Recirculation) passage can hinder the proper recirculation of exhaust gases, which helps reduce combustion temperatures and can contribute to detonation. Excessive machining of the cylinder head can affect the compression ratio, which directly influences the engine's tendency to ping.

Therefore, while fueling has an impact on performance, it is more accurately considered in the context of spark knock and does not serve as a direct cause of detonation like the other options listed.