Engine cant start, when driving its gutless

Even after driving when the engine is still hot, it cant start. The speed pedal is pressed fully to the floor but the car is not driving as expected. On the hills it give ups. The car is not giving any black smoke. The temperature gauge is normal goes only till the half mark but within short distance. After consulting the mechanic he said that it may be the fuel pump but he was not sure, if needed be then I will change the engine because there is no other problem related to it.