[quote="arsalaanali89, post:1205, topic:184235, full:true"]
Dear there is nothing like TUNING THE CAR for modern efi vehicles. Tuning is usually done for carburetor vehicles but since people know much about the technicalities, our mechanics exploit this as leverage for undue gains. So next time dont spoil your money for TUNING your car.
Your question, well it can be many things. Start off with the fuel rail and injectors. Get them checked, if injectors are clogged or leaking fuel, both mileage will reduce and performance will be affected. Secondly get the fuel pump assembly checked. If the fuel pump is not maintaining appropriate pressure, which is around 42-48psi at 2000 rpm, the ECM will widen the injector pulse width which will reduce your mileage considerably. Get both the fuel filter and restrainer filter checked and change if necessary. Lastly do check the fuel tank for rust / debris. Keep your fuel tank and fuel lines clean so that the injectors dont clog up and fail ultimately. Fill your tank with fuel from good service station and enjoy. Use high octane along with regular fuel so that the fuel system remains happy 
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in my humble opinion the word 'TUNE' is good enough to be used for any engine be it diesel, petorl, fuel injected, carburetor or nozzle one