This manuscript presents a fault detection method for a SI engine at variable speeds using acoustic signal technique. Two faults were addressed: misfire and the malfunction of manifold absolute pressure (MAP) sensor. The main objective is to detect these two faults by measuring the sound pressure level (SPL) in decibels (dBA) at different engine speeds and one octave frequency bands in the audible human range, and then compare the results to the normal operating SPL engine. The experiments were conducted using a four cylinder, four stroke spark ignition Mitsubishi Lancer sedan engine (1.6 L) model 2006. The experimental results showed that: 1) the SPL due to misfire malfunction increases as the engine speed decreases; 2) at low frequencies the difference between the two values of SPL is very small compared at high frequencies; 3) the curve shape for SPL follows the shape of the power produced from the engine.
Keywords: acoustics, misfire, manifold absolute pressure, MAP sensor, malfunction, SI engine