[Konstantinos]

What if it is unset (-1)? You don't check that:

pawn Код:

if(engine == VEHICLE_PARAMS_OFF || engine == VEHICLE_PARAMS_UNSET)

and health is float so you should declare a variable with Float: tag and use "f" specifier at sscanf.

pawn Код:

CMD:sethp(playerid, params[])
{
    if(PlayerData[playerid][AdminLevel] < 1) return SendUnathorizedMessage(playerid);
    new target, Float: vita;
    if(sscanf(params, "uf", target, vita)) return SendClientMessage(playerid, COLOR_SEABLUE, "{999999}Uso:{FFFFFF} /sethp [ID/Parte del nome] [quantitа]");
    if(IsPlayerConnected(target)) 
    {
        if(!gIsPlayerLoggedIn[target]) return SendPlayerNotLoggedInMessage(playerid);
        SetPlayerHealth(target, vita);
        new string[128];
        format(string, sizeof(string), "{999999}SERVER:{FFFFFF} Un admin ti ha settato gli HP a %.0f", vita);
        SendClientMessage(target, COLOR_WHITE, string);
        format(string, sizeof(string), "Admin:{FFFFFF} %s ha settato a %s gli HP a %.0f", GetPlayersName(playerid), GetPlayersName(target), vita);
        SendAdministratorMessage(string); 
    }
    return 1;
}