Muffler hole affecting O2 sensor readings, increase fuel consumption?

I have a hole in the muffler (rear silencer) will this affect power and increase fuel consumption by throwing off the 02 sensor readings?

Jjb0800 wrote: ↑Sun Mar 20, 2022 12:29 pm I have a hole in the muffler (rear silencer) will this affect power and increase fuel consumption by throwing off the 02 sensor readings?

No, the O2 sensor for fuel trim is at the other end of the exhaust system, up at the manifold.

Having a second hole in the end of the exhaust will have little effect of fuel consumption because there is already a hole in the end when they come out of the factory.

The rusty back box is a common problem on the C3 and not expensive to replace, see new parts on eBay.

Your biggest problem may be that you have the original exhaust system fitted and you need to measure correctly where to cut the full system to just fit the repair back box section.