I have been chasing a P1275 CEL code that I started getting when I put headers and 100-cell cats on the car. I replaced all 4 oxygen sensors at the same time that the headers/cats were installed.
Shortly after the installation I started getting the P1275 CEL code, which pointed us to low efficiency from the cats or oxygen sensors. We first checked the oxygen sensor wiring and it seemed to check out fine.
BTW, the car has had the CPU reprogrammed to take into account the headers and high-flow cats. The last time we looked we got the P1275 and it said the left bank was running at low efficiency. We then swapped both pre-cat and post-cat oxygen sensors on the left and right side and again got the P1275 saying the left bank was still bad.
That made us think it was a bad cat on that side, so we replaced the cat on that side last week, and again got the P1275 CEL, any ideas on what might be going on would be greatly appreciated,
Ed
