There is no quick fix to a stopped up convertor. They are welded on from the factory into the exhaust manifold down pipe. A low vacuum reading will usually indicate a bad convertor. You can pay lots of $$ for a factory replacement or a reman unit or, if you can find someone to do the work, buy a couple of those generic catalytic convertors which sell for about $39.95 ea and have them welded on. Much cheaper and will work just fine.