To test cylinder compression on a diesel engine, which component should be removed?

To test cylinder compression on a diesel engine, removing the glow plug or injector is essential because this allows for an unobstructed path for the compression gauge to be inserted directly into the combustion chamber. By doing so, you can measure the pressure directly within the cylinder while the engine is turned over.

In diesel engines, the glow plugs aid in starting the engine but are not necessary to have in place during a compression test, making their removal practical for this testing procedure. Removing the injector also achieves the goal of accessing the cylinder for accurate compression readings. This practice helps ensure that any fuel or other obstructions do not interfere with the measurement process.

The other components listed do not serve the same purpose for accessing the combustion chamber. For example, the throttle body and air intake are more relevant in controlling airflow into the engine rather than providing access for compression testing, while the fuel pump is part of the fuel delivery system and does not interact with cylinder pressures directly. Thus, the removal of the glow plug or injector is the most appropriate choice for conducting a thorough and accurate compression test on a diesel engine.