What is the reason for the car engine shaking when burning gas but not when burning oil?
4 Answers
Car engine shaking when burning gas but not when burning oil may be caused by fuel system failure, clogged gas injectors, throttle wear, etc. Below is a detailed introduction about the car throttle: Overview: The throttle is a controllable valve that regulates air intake into the engine. After entering the intake pipe, the air mixes with gasoline to form a combustible mixture, which then burns to generate power. Connected to the air filter at the top and the engine block at the bottom, it is known as the throat of the car engine. Classification: Throttles are divided into traditional cable-type and electronic throttle types. The traditional engine throttle control mechanism operates via a cable (soft steel wire) or rod, with one end connected to the accelerator pedal and the other to the throttle linkage plate. The electronic throttle mainly uses a throttle position sensor to control the throttle opening angle based on the engine's required energy, thereby regulating the amount of air intake.
My modified LPG car runs smoothly on gasoline but starts shaking when switched to gas. This is mainly because gaseous fuels like liquefied petroleum gas burn slower than gasoline and have lower energy density. If the ECU's ignition timing isn't properly adjusted after conversion, it can easily lead to uneven combustion. For example, gasoline ignites at a lower temperature, while gas is harder to ignite under high load or low temperatures—especially if the spark plugs aren't replaced with compatible ones or are fouled with carbon deposits, resulting in weak ignition. Additionally, the air-fuel mixture ratio needs to be more precise in gas systems. If the injectors are miscalibrated or the filters are clogged, the system becomes erratic. I had a mechanic check it and found that loose electrical connections can worsen the shaking. Regular maintenance of the LPG components is essential; otherwise, you'll feel the steering wheel tremble while driving, wasting fuel and damaging the engine. After conversion, it's recommended to test the system every six months.
I've encountered this situation several times while driving my own car. It runs fine on gasoline, but when switching to gas, the shaking becomes noticeable, especially during startup or climbing. It feels like the engine is hiccuping. At first, I thought it was a tire issue, but later a mechanic explained that the heat value of gas combustion is different. The factory spark plugs were designed for gasoline, and after converting to gas, the ignition efficiency decreases, leading to easier carbon buildup and aging. Also, the air-fuel mixture wasn't adjusted properly—too lean, causing slow flame propagation and unstable cylinder pressure. After replacing the spark plugs and cleaning the fuel injectors, it improved somewhat. The gas system is more sensitive than the gasoline system. If maintenance is neglected, such as gas leaks in the pipes or sensor failures, the shaking becomes frequent. In owner groups, it's often shared that warming up the car longer in winter can help, but don't overlook inspections.
The most common issue with modified gas systems is improper calibration causing engine vibration. Gasoline engines are originally designed for liquid fuel, requiring precise adjustments to ignition timing and fuel injection when running on gas. Otherwise, the air-fuel mixture becomes imbalanced, leading to incomplete combustion and significant cylinder pressure fluctuations. Installation details such as loose connections and airflow meter errors are also critical. In cases I've handled, I found that improperly reset ECU parameters or user-modified settings can both cause instability. Professional modifications should inspect all connection points to ensure system sealing reliability.
