Quote:
Originally Posted by wstar
It would be difficult, if not impossible, for a functioning catback to cause you to throw an O2 CEL. I haven't heard of anyone getting a CEL from the Berk HFCs either, including me, and given that the O2 extension on the FI ones is even more aggressive I wouldn't expect one there either.
With test pipes you have to expect at least a good probability of an O2 CEL, unless you block them off really good.
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Correct, the cat back will not cause a CEL light. Your 2 rear O2 sensors located within your stock cats are for emissions. When you take off the stock cats and relieve that much back pressure you create 2 things instantly. 1) You increase the velocity of the exhaust, 2) You reduce heat. Now in order for your rear O2 sensors to work properly they need to take a reading within a certain parameter and stay hot. Now back to the velocity aspect. By increasing the exhaust flow your rear O2 sensors will sample too large of a reading. In turn it sends it back to your ECU and reports the problem. Your ECU then trips your CEL light to make you aware of the problem. By relieving the back pressure your EGT (Exhaust Gas Temperature) decreases, hence less heat. By having our U Bend style O2 sensor non fouler you keep the heat up and the reading down.
Now it is extremely effective with high flow cats. Reason being, the cats are not free flowing and they will help produce enough heat as well as restriction. With the Resonated and straight test pipes the non foulers are effective most of the time. However, there is that seldom case where they do not keep the CEL light off. In the event of that, the only way to eliminate the CEL light is the reflash the ECU with a tune, EX: Uprev, Technosquare and Cobb.