Why does the car body shake slightly when the engine shuts off?
2 Answers
The reasons for engine shaking during shutdown are as follows: 1. Excessive carbon deposits: This may cause premature ignition and detonation, reducing engine lifespan and significantly decreasing power and fuel efficiency. 2. Valve carbon buildup: Carbon deposits on valves and seat rings can lead to incomplete valve closure and air leakage, resulting in hard starting, weak operation, and valve erosion. 3. Valve guide carbon buildup: Carbon deposits on valve guides and stems accelerate wear and may cause sticking or seizure of valves. 4. Piston ring groove carbon deposits: These reduce clearance, causing piston rings to lose elasticity and potentially leading to cylinder scoring. Injector carbon buildup causes uneven fuel distribution, resulting in engine shaking or misfiring. 5. Excessive spark plug carbon deposits: This can cause spark plug leakage, non-functioning, and engine shaking.
Having driven for over twenty years, I've encountered quite a few instances of shaking upon engine shutdown, which are mostly related to the engine's operating condition. Especially with older cars, it could be due to excessive carbon buildup inside the engine or clogged fuel injectors causing incomplete combustion of the air-fuel mixture, resulting in a couple of shakes when stopping, much like a person coughing. Another common cause is the aging of engine mounts; over time, the rubber components harden and crack, reducing their damping effect, so the engine vibrations directly transfer to the car body upon shutdown. I've also experienced poor contact in ignition coils, where unstable ignition voltage leads to uneven engine operation. It's advisable to first read the trouble codes to check for issues like cylinder misfires or oxygen sensor problems. For daily maintenance, using fuel additives and periodically cleaning the throttle body and fuel injectors can effectively alleviate shaking issues.
