The key to diagnosing many cranking, no-start and stalling problems found on the late-model import is to understand how the crankshaft and camshaft position sensors function and what their mechanical relationship is to each other. During the past 30 years, ignition control systems have evolved from distributor-type, to distributorless, to coil-on-plug ignition systems. Similarly, fuel injection systems have evolved from carbureted to throttle body to "banked" multiport to sequential multiport systems. Quite obviously, it's more important than ever to understand how the crankshaft and camshaft sensors function in each of these systems.

Going back to the basics, the Otto cycle engine requires two revolutions to complete one combustion cycle. The first revolution of the combustion cycle is composed of the intake and compression strokes. The second revolution is composed of the power and exhaust strokes. The purpose of the crankshaft (CKP) and camshaft position (CMP) sensors is to determine whether the crankshaft is on the first or second revolution of the combustion cycle, and to also determine which stroke is occurring in each cylinder.

MODERN FUEL INJECTION SYSTEMS
The function of the distributor on throttle-body injected engines is to determine when each cylinder reaches top dead center (TDC) on the compression stroke. When the cylinder reaches TDC, th...