If there's carbon built up on the oxygen sensor it probably won't send a signal but it will read incorrectly. What did you fail in? CO and HC?
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'84 Mustang 5.0 T5, FMS aluminum radiator & 180* thermostat, 1 5/8 shortys/2.5" duals, '88 GT tail lights and wheels, Holley 4160 4 BBL, smog pump idler, now with hi-po collapsed lifters in #3 or #4
