PO420 & Catalytic Converter question
I'm getting a PO420 code from my OBD. I have a Flowmaster exhaust, but the catalytic converters are OE on my 2005 Dodge Ram 1500 5.7. I'm probably going to replace both sides with Flowmaster catalytic converters (along with new bolts, etc.), but I'm unsure if I need to get an exhaust pipe flange gasket (donut) to mate the new pipe with the old exhaust manifold. I'm pretty sure I do, just never done that before. Any advice? Any recommendations on Walker versus Felpro, etc.?