You can run it without, had an s-10 without it, and the light only came on after about 15-20 minutes of highway driving. Never came on in town. I would check the codes, but 8mpg sounds clogged to me. Once you get it off give it a tune up. They used to make a "test" pipe that would fit where the converter was, with flanges and all, not sure if those are still around? I drilled one out once, but even with a mask would not do that again, you should be able to get some money for it at a yard for the platinum.