[Logic_]

Make your timer be called every 1 second (1000 ms).
Update your foreach to the latest version; The latest one uses different syntax of foreach(new i : Player).
No need to make several arrays (or strings), you can use one array and re-use it.
I made vehicleid variable and stored the ID, so I don't need to use the GetPlayerVehicleID function over and over again.

PHP код:

public Speedometer(playerid)
{
    new string[32], vehicleid;
    foreach(new i : Player)
    {
        if(!pInfo[i][Logged]) continue;
        vehicleid = GetPlayerVehicleID(playerid);
        if(vehicleid)
        {
            format(string, sizeof string, "~g~%s", VehicleNames[GetVehicleModel(vehicleid) - 400]);
            TextDrawSetString(VehicleName[i], string);
            format(string, sizeof string, "%d", GetPlayerSpeed(i, 0)); 
            TextDrawSetString(VehicleSpeed[i], string);
            GetVehicleHealth(vehicleid, vhealth);
            format(string, sizeof string, "~%s~%.0f.0", DamageColor(vhealth), vhealth);
            TextDrawSetString(VehicleHealth[i], string);
        }
    }
    return 1; 
}