B8 Audi S4 running rich both banks after exhaust work
About 4 weeks ago I had a resonator delete done at a shop. O2 codes appeared day 1, car drove fine for 2 weeks, then progressively got worse. Now it idles rough when warm (fine cold), has hot restart issues where it jerks and stalls after driving, and there’s a rich fuel/metallic smell from the exhaust. Drives completely fine under load though, pulls hard, no hesitation.
OBDeleven shows both banks running severely rich — STFT maxed at -37.5% both sides, LTFT Bank 1 at -9.4% but Bank 2 at -59.4%. Downstream O2s are pegged at 0.85-0.96V confirming real rich combustion. Fuel pressure is 34 bar at idle but climbs properly to 110 bar under load so HPFP seems healthy. Coolant temp normal at 90°C. Codes are P2237 (persistent), P2240, P1127, P1129, P0133, P0153, P0136, P0156, P0068, P1158, plus P0491/P0492 that have always been there.
PCV was replaced at 180k km with a ÜRO (AC revision) so it has 52k on it. A week ago I made things worse by replacing 3 of 4 O2 sensors with cheap Amazon aftermarket because I assumed they were the problem. Now I’m stuck between theories: leaking injector on Bank 2 (fits the hot restart stall and bank asymmetry), exhaust leak from the shop weld affecting O2 readings, ÜRO PCV failing early, or some combination. The severity and timing point to the shop work triggering something, but I’m not sure if they directly damaged sensors or caused an exhaust leak.
Going to an Audi specialist this week for an injector leak-down test and physical inspection. Anyone seen this exact pattern on a B8 S4, or have experience with ÜRO PCVs failing early? Appreciate any insight before I walk in.