If you car does not have a knock sensor, DO NOT go below the rated octane requirement as noted on the fuel lid/owners manual. You could damage your engine if you run long term with the lower than recommended rating.
Saga/Wiras do not have knock sensor , or any cars with a carburetor, or older cars. So run with the proper fuel.
If you own a Saga/Wira, you could ask your mechanic if it is possible to retard the ignition timing to allow you to run RON95. Usually its just turning the distributor to retard a few degrees. Takes 10mins. You will feel the power loss.
For newer cars that have knock sensors, there is no issue. You can run as low as you want with the expense of a power loss.
You don't have to worry about damage since the engine ECU will automatically adjust the ignition timing to compensate.
What is knock sensor?
A knock sensor is fitted to some management systems, the sensor being a small piezo-electrical device that, when coupled with the Electronic Control Modules (ECM), can identify when knock occurs and retard the ignition timing accordingly.
The knock sensor picks up when the ignition is too far advanced for the load on the engine. The ecu receives a signal from this sensor and retards the ignition to suit.
It is an "active" signal since the ECU nearly always trying to run the timing as advanced as possible.
Knock sensor detects engine knock and sends a voltage signal to the ECM. The ECM uses the knock sensor signal to control timing. Engine knock occurs within a specific frequency range. The knock sensor, located in the engine block, cylinder head, or intake manifold is tuned to detect that frequency.
The knock sensor senses when fuel is burning unevenly and causing “knocking” or irregular vibrations in the engine. It consists of an electric coil that is wound around two ceramic rods with a magnet in the center. The vibration of the engine causes the rods to vibrate. This disturbs the coil’s magnetic field and alters the current passing through the coil. This disturbance returns to the computer as a signal pattern that the computer analyzes. The computer then determines whether the vibrations are characteristic of engine knocking.
Although the knock sensor is tuned to pick up the vibrations caused by knock, typically around 4KHz, it is possible for a knock sensor to 'hear' other signals which the ECU interprets as knock.
Things that are loose, rattling or impacting together can confuse a knock sensor. If the bolt is too loose, or too tight, the centre frequency of the sensor can be incorrect, so the sensor might pickup the valve train noise rather than knocking, for example.
Also, as the knock sensor signals are very small, they are easily swamped by electrical interference and noise. The noise may be interpreted by the ECU as knock. Some of the mechanics recommend fitting metal braiding over the knock sensor wires, effectively extending the ECU metal casing all the way to the sensor, in order to shield out electrical noise.
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