Update Node Problematically is not working fine
You can try to load node with its id :  

   $nodenew = node_load(14); // load the complete node


So when you use node_save() all other field values that was previously stored in database will automatically get loaded. Then only thing remains is the field you want to update.

   $nodenew-&gt;field_site_url[$array_id]['value']=$website_url; 
   $nodenew-&gt;revision=1;
   $nodenew-&gt;created = time();
   $nodenew-&gt;changed = $nodenew-&gt;created; 
   $nodenew-&gt;comment = 0; 
   $nodenew-&gt;type ='product';
   node_save($nodenew);