Put guava slices into a deep pot and cover with water; bring to a boil, reduce heat, and simmer until fruit is tender.
Measure fruit and add an equal amount of sugar.
For 4 cups of fruit, use 2 limes.
Discard center and core from lime halves and squeeze.
Add the juice and shells to the fruit and sugar.
Cook at a rolling boil 10 minutes.
Pack hot mixture into sterilized jars, seal, and store.