there are three, one on each manifold (upstream) and one near the converter(downstream) the upstreams are (bosch number)15717's the downstream one is a 15718 (bosch again) remember to get a good o2 sensor socket, and lots of pb blaster
(these numbers are for the automatic)

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2000;3.0 vulcan;flowtech raptor muffler; no cats;k&n oil filter;goodyear wrangler tires;spectre cold air intake;200 watt pioneer headunit with 2 kenwood jl-80 boxes holding 2 10 inch pyle subs, 2 kenwood 4x6 2ways and 2 polkaudio 4x6 plates and two xplod 3 ways in the doors;plenty of scratches dings and dents, chipped (flashpaq)