Vehicle is a 2004 Mercury Monterey, V6. Over the winter the injectors were replaced, and all 4 O2 sensors. It failed a state inspection, because the catalytic converter had been damaged, presumably from running lean prior to the injector problem being diagnosed. The new catalytic converter is in, but now is showing P0171 and P0430 error codes. What are the likely culprits? It seemed immediately after the install that some exhaust may have been leaking around one of the flanges between the exhaust pipe and the manifold, but all 4 bolts (2 for each connection to the manifold) seem very tight now.

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    Welcome to Motor Vehicle Maintenance & Repair! Two things: first, did you clear the codes again after they came up? Second, did you break in the catalytic converter upon first startup? Also, a lean condition should not hurt a cat ... it's a rich condition which will ruin them. Commented Aug 3, 2020 at 0:53
  • Thank you for the welcome, and for taking the time to comment! There were no codes showing at the point the new catalytic converter was installed. The materials that came with the new catalytic converter said that no break in was required- is there still a procedure that is best to follow even if the materials say it isn't required? It has Commented Aug 3, 2020 at 1:02
  • Try this link. Commented Aug 3, 2020 at 1:05
  • Do you think that could be the cause for the codes? It was only idled for a short period of time. The engine warmed up, but it wasn't an extensive idle. Commented Aug 3, 2020 at 1:11
  • You could try, but I really don't know. You may also need to let it be running longer (after you try to break in the converter) and see if it wakes up the converters. Commented Aug 3, 2020 at 1:14


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