Postby VStar650CL » Mon Aug 22, 2022 7:46 am
If it isn't throwing codes then most likely it's one of the rear converters going bad, you can replace those with a straight pipe with no issues at all. Front cats are more complicated because you need to either install emulators to fool the ECM into thinking the rear O2's are still present, or get an ECM tune so the ECM quits looking for them. First thing I'd do is find out which cat is making the stink. Warm the engine completely with a highway run, then aim an IR thermometer at each cat. They should all be substantially hotter at the outlet than the inlet. One that's less than +30F or so is dying, one that's the same temp or cooler at the outlet is completely dead.