Thanks for writing. If your morning glory wilts a little during the heat of the day, but recovers at night, it's usually not a problem. The plants sometimes lose more moisture from the leaves on hot, sunny days than the roots can absorb. If the plants recover at night they should be fine.
That said, do be sure the plants get enough moisture. Morning glories are not super drought tolerant. Also: Do you if the area has been urinated on much by dogs? If so, there could be a high concentration of salts in the soil, and that could be what's giving your vine a hard time. Flushing the soil with lots of water can help dilute the salts.
---Justin, Senior Garden Editor, BHG.com