Diagnosing Engine No-Start

The engine is spinning but not running. You have a battery and starter that work — the problem is in fuel, spark, or compression. Figure out which one is missing.

Pull a coil and plug from one cylinder. Reinstall the plug into the coil. Ground the plug threads against the engine block. Have someone crank the engine while you watch for a spark at the plug gap. Spark present — ignition is working on that cylinder. No spark — check for crank sensor signal with the scan tool. No crank signal means no spark and no fuel on most vehicles. The crank sensor is the most common cause of a crank-no-start with no codes.

Turn the key to ON without cranking. Listen for the fuel pump hum from the rear — a two-second buzz means the pump is priming. No hum — check the fuel pump fuse and relay. If the pump runs, check fuel pressure at the rail with a gauge. Zero pressure with the pump running — the pump has failed internally or the fuel line is blocked. Low pressure — weak pump or restricted filter.

If you have spark and fuel but the engine will not fire — compression test all cylinders. A jumped timing chain or broken timing belt causes zero or near-zero compression on all cylinders because the valves are not opening and closing in sync with the pistons. This is the classic crank-no-start pattern on engines with timing belt or chain issues — the engine cranks faster than normal because there is no compression resistance.