Just thought I'd send up a flare here, my neighbor's '97 BMW 328i is failing smog with high Hx numbers. He has replaced the cats, car runs great, new tune-up parts, (plugs, etc.).
He thinks that the aftermarket cats might be defective, I say unlikely since they are pretty simple devices. Can you guys think of any place else to look before he tears his exhaust off again and brings them back? Oh yeah, car is not throwing any fault codes.
TIA, he's a friend and I want to help him but don't know what to tell him.
