I’ve only done this with old versions of WP and found it only worked when using Blogger methods. Below is the code I used, maybe it will be of some help to you.
$client = new xmlrpc_client($xmlrpcurl);
$params[] = new xmlrpcval("n/a");
$params[] = new xmlrpcval("n/a");
$params[] = new xmlrpcval($username);
$params[] = new xmlrpcval($password);
$params[] = new xmlrpcval("<title>" . $postTitle . "</title>" . $postContent);
$params[] = new xmlrpcval(false);
$msg = new xmlrpcmsg("blogger.newPost",$params);
$response = $client->send($msg);
if ( $response->errno == 0 ){
print 'Success';
} else {
print 'Fail';
}