AJAX :: Google Maps V3 Marker Updating

I'm trying to update the location of a marker in a Google Maps API. The only problem is that the marker won't update (only if i update the whole initialize() function with a setTimeout function).

It goes about the following code:

Code:

What i want is that the marker updates automatically (with AJAX) and not the whole map. First of al i thought i push the code that set's te marker in a function, and reload that every 4 seconds. But that doesn't work.