new Gas[MAX_VEHICLES];

OnGameMode:
for(new i = 0; i < MAX_VEHICLES; i++)
{
 Gas[i] = 100;
}

SetTimer("CheckGas", 180000, 1);

stock VehicleEngine(vehicleid, bool:toggle)
{
    GetVehicleParamsEx(vehicleid,engine,lights,alarm,doors,bonnet,boot,objective);
    if(toggle == true)
    {
        SetVehicleParamsEx(vehicleid, VEHICLE_PARAMS_ON, VEHICLE_PARAMS_ON, alarm, doors, bonnet, boot, objective);
    }
    else
    {           
        SetVehicleParamsEx(vehicleid, VEHICLE_PARAMS_OFF, VEHICLE_PARAMS_OFF, alarm, doors, bonnet, boot, objective);
    }
    return 1;
}

stock GetDriver(vehicleid)
{
    foreach(Player, i)
    {
        if(IsPlayerInVehicle(i, vehicleid) && GetPlayerState(i) == PLAYER_STATE_DRIVER)
            return i;
    }
    return -1;
}

public CheckGas()
{
    for(new i = 0; i < MAX_VEHICLES; i++)
    {
        Gas[i]--;
        if(Gas[i] == 0) 
        {
            VehicleEngine(i, false);
            GameTextForPlayer(GetDriver(i), "no fuel left", 5000, 3);
        }
    }
    return 1;
}