I have recently acquired a 1999 Toyota Sprinter (Japanese domestic import). I realised that the engine "ping" so someone recommend to use 90 Octane petrol. I went through the manual but it only says "Unleaded Gasoline Only" but does not tell what octane rating to use. Does anyone knows this??? The problem is, sometimes it still ping. What else could be the reason for this?? I intend to visit a mechanic soon but I want to gather as much information before. Additional information: it pings more with the "mixed" fuel (E-10) compared to the pure petrol without the ethanol. Is this possible for this type or any type vehicle?
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Your vehicle requires 95 or 97 octane fuel. Any lower rated octane fuel will give you the engine pinking and knocking you describe.
When your mechanic gives the vehicle his/her attention, ask that the engines 'knock sensor' is checked for correct operation. Also that the 'engine temperatures' are within specification.
In a simple description, lower octane fuel explodes, high octane fuel burns rapidly Higher octane fuel allows greater control over the ignition event, which is what is required.
Modern vehicles coming to market, Cherokee Jeep relaunch and some VW's, will have 9 speed transmissions. This means at 70 mph the engine will have an rpm of around 1750 rpm. This lower rpm lends itself to a full control of engine power, emissions and engine life.
It sounds like you have carbon buildup in your combustion chambers. A thorough intake tract cleaning should take care of it. You can get it done at the shop, or there are treatments you can do at home (ie: Seafoam). What happens is the carbon buildup creates hot spots in the combustion chamber which pre-ignights the air/fuel mixture and causes the ping or knock sound.
Your friend was right to suggest a higher octane fuel. The rule of thumb for a car is to run the lowest octane fuel you can without the pinging unless your car states a specific fuel. Cars that run a higher octane fuel are usually high performance vehicles, like a Corvette, or if it runs a turbo charger, like in the VW and Audis. If your car can handle the lower octane, you will get better fuel mileage from it. Running higher octane than the engine requires is just through in money away unneedlessly.
There is a huge misconception about Octane in that the higher the Octane rating, the better it will burn, when in actuality it is the opposite. The higher octane will actually make it harder to burn.