relacing parts, still not fixed

[Smallblock454]

Hi,

yes, if you have a faulty gasket on the manifold, the o2 sensors detect too much o2 and this will generate a DTC. Also P1126 That is usually a lean condition on Bank 1. Means too much o2. So i would recommend to check all gaskets on bank 1 between engine and the o2 sensors. If there is an exhaust leak on the manifold to cat, this will be the problem.

Regards, Markus