Well thats the odd part of the equation, it doesnt happen to all cars. Some guys with as little as an off-road non cat'd downpipe have problem or most guys that have modded cars with no cats see this. What I really think that is happening though is that HOW many people actually scan their cars continuously while driving every day to even know this is going on? Some cars wont show the bad side effects as much as others tune and mod dependant. Unless you have a scan gauge or something in the car and are watchin LTFT driving for a long time you may not even know the problem exists. An 02 sim will not cover this problem up because all it does is constantly switch the voltage to make the pcm think it is working properly. If the pcm throws more fuel at the engine for the cat diag to make it run rich it also wants to see the rear 02 follow this, a sim will keep bouncing the voltage around and not provide the data that the pcm wants to see.
