Why does the engine shake when using 92 octane but not with 95 octane?
2 Answers
Using 92 octane fuel causing engine shake while 95 octane doesn't is due to fuel system malfunction. Adding incompatible fuel grades (e.g., using 92 octane instead of 95 octane) leads to decreased vehicle power output and reduced performance. Here are other reasons for engine shaking: 1. Aging or loosening of engine mounts. Engine mounts are rubber blocks placed between the engine and the frame. Their purpose is to reduce vibration and cushion the engine's operation while securing it in place. Once these mounts age or loosen, engine shaking becomes noticeably abnormal. 2. Engine misfire. An engine misfire refers to one or more cylinders not functioning properly, resulting in noticeable engine shaking, sometimes accompanied by sputtering sounds. This is often related to ignition coil failure. 3. Carbon buildup issues. Carbon deposits can accumulate in various parts, including cylinders, throttle valves, spark plugs, and intake systems. Excessive carbon buildup inside the engine reduces ignition energy and intake efficiency, ultimately causing symptoms like engine shaking and poor acceleration.
I’ve experienced this issue with my older Japanese car before, mainly due to differences in gasoline octane ratings affecting combustion. 92-octane fuel has weaker anti-knock properties, and when paired with a high-compression engine or severe carbon buildup, the elevated compression temperatures can cause premature ignition, resulting in knocking. The irregular shockwaves from knocking transmit to the steering wheel as that jerky vibration. Switching to 95-octane fuel improves anti-knock performance, stabilizing combustion and eliminating the shake. Long-term use of low-octane fuel is harmful—knocking not only degrades driving comfort but also worsens piston ring sealing. Always refuel with the octane grade specified in the maintenance manual. For older cars, consider a combustion chamber carbon cleaning first; otherwise, the premium fuel’s benefits will be wasted.
