P0420

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Cats and sensors replaced with Bosal and Denso about 2k miles ago. Code returned recently. Exhaust is now new from engine to tailpipe. LTFT at 2K is at 16%. Have smoked it several times, repairing leaks as I find them (leaking EGR to intake gasket, cracked upper resonator tube, cracked intake tube, cracked EGR vacuum control valve vacuum tube). After repairs, the codes are cleared and we attempt to set readiness, but code returns, and LTFT really doesn't drop. Only one code appears. I have the graphs of the o2 sensors (a/f sensor) as well as freeze frame screen shots, but I am not sure how to post them.