2 To effectively listen to the engine during a continuous crank, begin by engaging the engine without starting it. This process varies depending on the make, but on American cars and Mazdas, it’s simplified by a feature called Clear Flood Mode. First, turn the key to the on position, allowing a brief pause. Then, fully depress the gas pedal before attempting to start the engine. It will crank persistently without starting as long as you maintain the key turned or, in the case of push-button start vehicles, until you press the button again.
To effectively assess engine compression, pay close attention to the engine’s behavior during the cranking process. If the engine starts, promptly release the gas pedal to prevent excessive revving before attempting to start it again. Take your time to listen attentively for approximately 10 seconds. This simple procedure serves as a convenient method for checking engine compression. During cranking, the primary sound you’ll notice is the electric starter’s efforts to spin the engine. As a piston rises and compresses the air within the cylinder, the starter encounters increased resistance, necessitating greater effort to rotate the engine. This heightened workload manifests in changes to the starter’s speed and pitch, offering valuable insights into the engine’s compression levels.
Understanding the nuances of engine sounds is key to diagnosing potential issues. As the piston completes its compression stroke and descends, the engine becomes easier to spin, resulting in a return to the original speed and pitch of the starter. This cyclical pattern repeats with each subsequent piston’s movement during the compression stroke. While engine sounds vary, they should all exhibit a consistent and rhythmic starting noise, often described as a repetitive “WAAA WAAA WAAA” pattern. However, if one or more cylinders suffer from low compression, the starter’s sound becomes irregular. For example, in a four-cylinder engine with a single cylinder experiencing low compression, the rhythmic pattern would be disrupted, manifesting as “WAAA WAAA WA WAAA WAAA WAAA WA WAAA WAAA WAAA WA,” where every fourth pitch change differs from the others. This distinctive alteration in rhythm serves as a telltale sign of potential compression issues in that specific cylinder. By recognizing these deviations, you can efficiently identify and address engine performance concerns.
To help you differentiate between a normal cranking sound and the sound of a low compression cylinder, here are two audio references.
First, a normal cranking sound can be heard in this video: Normal Cranking Sound.
Secondly, listen to the sound of a low compression cylinder at approximately 0:55 seconds into this video: Low Compression Cylinder Cranking Sound.
