What causes a popping sound when starting a car that has been parked for a long time?
1 Answers
Due to ignition delay, unburned gasoline is just being discharged into the exhaust pipe when the spark plug ignites, causing the atomized gasoline to ignite in the exhaust pipe and produce the sound. Below is relevant information: 1. The abnormal sound only occurs at idle or low-speed operation: Possible causes include: excessive clearance between the piston and cylinder wall; overly tight piston pin or connecting rod bearing assembly; excessive clearance between the tappet and its guide hole; wear on the camshaft profile; sometimes, a loose starter causing the pulley to make noise (especially noticeable during speed changes). 2. Brief successive sounds during rapid deceleration: Sounds become chaotic at certain RPMs, with brief successive noises during rapid deceleration. Possible causes include: cracked camshaft timing gear or loose fixing nut; broken crankshaft; loose piston pin bushing; excessive camshaft axial clearance or loose bushing.