I have an 86 Thunderbird with the 3.8L. It's throwing a 67 and a 31 when I run the engine off self test. When I run the engine on self test, it was throwing 12, 30, 31, 41, 44, 91 and 94. I suspected it was the spark plugs so I changed them. I saw that all plugs were fouled out and burnt around the edges as if the spark was missing the post. They had an enormous amount of carbon build-up. After changing the plugs, 3 codes went away (30,44,94). So I'm left with 31, 67 (engine off) and 12,31,41 and 91 (engine on). Could the O2 (HEGO) sensors be causing all of the other codes as a result of low voltage (bad sensors reading "lean" causing the engine to conversely run rich)? I'm hoping that changing the O2 sensors will fix the other codes. Also, where is the best place to get the sensors? All of my parts houses only carry "universal single-wire" replacements which must be spliced and i hate the idea of Doing that. I'd rather use OEM if I can find them at a reasonable price. Any help is appreciated. Thanks in advance.
