In a bowl, mix flour, chili powder, garlic powder and cumin together.
In a pitcher combine the cold water and white vinegar.
Put corn oil into a large stock pot. Heat oil until hot (a little
flour dropped into the oil will sizzle). Add flour mixture to hot
oil, whisking until it resembles coarse meal. Cook for 4 minutes
Quickly add 1/3 of the cold water, stirring
constantly to break up lumps. Add remaining water, stirring frequently
with the whisk. Add salt and sugar. Turn heat to medium high, continuing
to stir frequently until sauce thickens.