Nearly every driver who installs an LPG system asks the same question: "Why does the car run a bit differently on gas?" The short answer is that petrol and LPG are two different fuels with different properties. But there is a clear line between a normal difference and a problem that needs fixing.
Different Fuels, Different Combustion
Petrol is a liquid fuel that gets injected into the cylinder and evaporates. LPG (liquefied petroleum gas) enters the engine already as a gas. Because of that, the combustion process is different.
Combustion speed. LPG burns slightly slower than petrol. This means the engine may respond a little differently to sudden throttle changes, especially during hard acceleration. On a well-calibrated system, this difference is barely noticeable.
Energy content. A litre of LPG contains less energy than a litre of petrol, roughly 15-20% less. That is why LPG uses more litres, but since the price per litre is significantly lower, the bottom line always favours LPG.
Combustion temperature. LPG burns at a slightly higher temperature than petrol. This is why proper mixture calibration matters so much. A well-tuned system compensates for this difference, while a poorly tuned one can put extra stress on the valves.
What Counts as a Normal Difference
There are things that are perfectly normal and should not be treated as a problem:
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Slight power loss (5-10%). Due to the lower energy content of LPG, a small drop in power is physically unavoidable. In everyday driving, most people do not even notice it.
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Slightly different engine sound. LPG burns differently, and the engine may sound a bit quieter or just slightly different. This is not a sign of trouble.
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Difference in response at full throttle. Under maximum load, the power difference is a bit more noticeable. Some systems have a feature that automatically switches to petrol at full throttle for exactly this reason.
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Brief pause during switchover. The moment while the system transitions from petrol to LPG (usually 1-2 minutes after starting) is a normal phase. A slight change in how the engine runs during that moment is nothing to worry about.
When the Difference Is Not Normal
These are signs that there is a real problem that needs attention:
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Noticeable power loss (over 15%). If you feel a significant difference in pulling power, something is wrong with the LPG system. Most often it is the reducer or a bad calibration.
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Jerking that does not happen on petrol. A normal difference is mild and continuous. Jerking, hesitation, or stumbling is always a sign of a problem.
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Check engine light only on LPG. If the warning light comes on only when you drive on gas, the system is not calibrated properly and the petrol ECU is detecting irregularities.
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Significantly higher consumption (over 25% difference). If LPG consumption is 30% or more compared to petrol, the problem is in the calibration, injectors, or reducer.
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The car switches back to petrol on its own. This means the LPG computer has detected a problem and activated its safety mode.
Why Some Problems Only Show Up on LPG
This is an important thing to understand. The LPG system is more sensitive than the petrol system when it comes to engine problems. A spark plug that is nearing the end of its life, a coil that occasionally misfires, a vacuum hose with a small leak: all of this might go unnoticed on petrol, but it shows up immediately on LPG.
That is why we say LPG sometimes acts as a diagnostic tool. If the car starts jerking on gas but seems fine on petrol, we check the engine condition first. In more than half the cases, the issue turns out to be spark plugs or coils, not the gas system itself.
How to Keep the Difference to a Minimum
Good installation and regular maintenance. That is the whole story. A quality LPG system, properly calibrated for your engine, with regular servicing every 10,000-15,000 km, will run so well that you will forget which fuel you are on.
If you feel that your car runs too differently on LPG, come by and let us take a look. Often a simple recalibration is all it takes to get things back to normal.