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Old 04-24-2017, 01:27 PM   #8 (permalink)
Deep Lurker
Join Date: Sep 2016
Location: Central Florida
Posts: 53

Creepy Van - '95 Ford E150 Cargo
90 day: 14.45 mpg (US)
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P0420 is probably caused by the lean misfire. That could be anything from a bad wiring connection to the injector or plug, clogged injector, bad spark plug, bad O2 sensor, etc. My wife's Miata would routinely throw a P0420 when the coil packs were dying. Nothing wrong with the cat, it was just getting a random misfire that made the computer think something was wrong with it. The computer never came up with a "too rich" or "too lean," go figure. At one point I had an injector die, and the stupid computer complained about P0420 instead of "cylinder 3 has no fuel."
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