Some apps and services run in the background when you're on Wi-Fi but not when you're on data. There could be something on your phone using a lot of bandwidth when you're connected to Wi-Fi. You can investigate by tapping your network icon in your phone's drop down to go to the "Data usage" screen, then tap the menu on the top-right and tap "Show Wi-Fi". Then switch to the Wi-Fi tab to see which apps are using the most bandwidth on Wi-Fi. If you don't find the culprit here, you can also reboot into safe mode and see if you can isolate the app or service responsible by opening things one by one as described in the troubleshooting guide: [[Motorola Moto G 3rd Generation Troubleshooting#Section_Weak_or_Lost_Wi_Fi_Connection]]