When troubleshooting issues with proxy auto-config (PAC) files and WinHTTP on Windows 8.1 you may wish to view the cached PAC files which the WinHTTP Web Proxy Auto-Discovery Service have written to disk. These cached PAC files can be found in c:\Windows\ServiceProfiles\LocalService\winhttp and are named with a nine digit number and a cache extension (eg: 1667635681.cache). There is also a cachev3.dat file which appears to contain the download location of the PAC file, the MIME type of the file, and the download date/time.
This can be discovered by using Process Monitor with a filter of Path contains winhttp when the WinHTTP Web Proxy Auto-Discovery Service is started (net start WinHttpAutoProxySvc).
thanks a lot! this article helped me to address an issue where the winhttp traffic always been sent to an unexpected proxy.