Lightly coat ears of corn with vegetable oil. Charbroil corn on grill, turning frequently until majority of kernels are dark brown. Remove kernels, cutting close to cob so as to remove as much starch as possible.
In a large pot, sauté onion and bacon until bacon browns. Add cumin and cook for another 2-3 minutes. Add corn to onion, then add water and chipotle. Boil slowly for 1 hour.
With a hand-held blender or food processor, puree soup on high speed 3-4 minutes. Add salt and lime juice. Strain through a china cap. Reheat to serve.