Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Interferon-gamma may interfere with the growth of tumor cells and slow the growth of the tumor. Combining more than one drug with interferon-gamma may kill more tumor cells. This phase I/II trial is studying the side effects and best dose of giving fluorouracil together with phenylbutyrate, indomethacin, and interferon-gamma and to see how well it works in treating patients with stage IV colorectal cancer