What is the purpose of performing a compression test during no-start diagnostics?

• A. To evaluate electrical continuity of the ignition coil.
• B. To measure exhaust backpressure.
• C. To check the engine's mechanical health by measuring cylinder compression.
• D. To verify fuel injector spray pattern.

Answer: (C)

The main idea is to check the engine’s ability to seal and trap air in every cylinder, which reveals the engine’s mechanical health. A compression test measures how much pressure each cylinder can develop when cranking, and this tells you whether worn rings, leaky valves, a blown head gasket, or timing problems are preventing starting. By comparing readings to the manufacturer’s spec and across cylinders, you can pinpoint if the no-start condition is due to a mechanical issue in one area or a broader problem.

This test isn’t about spark or fuel delivery. Electrical continuity of the ignition coil relates to spark generation, not the engine’s ability to compress air. Exhaust backpressure and fuel injector spray pattern concern flow and fuel delivery, not the sealing of the cylinders.