86 Thunderbird 3.8 throwing all kinds of codes

April 06, 2017, 04:11:55 PM

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.

86 Thunderbird 3.8 throwing all kinds of codes

Reply #1 – April 07, 2017, 07:48:07 PM

Engine off test (KOEO) codes are two parts. O codes (On demand) and M codes (Memory) O codes come out first, a separator pulse, then the M codes.
If the KOEO code 31 is a Memory code you will have to shoot the engine running (KOER) code 31.

Code 31--O--The EVP (EGR Valve Position) sensor voltage out of specs. With the KOEO the EVR voltage (BR/LG wire) should be between 0.5 and 1.25 Volts.
If above 1.25v the valve is not completely closed, maybe gunked up.
If below 0.5v check the O/W wire for 5v and the BK/W wire for ground.

Engine running tests (KOER)
Code 12--R--Self test could not reach fast idle RPM spec. shoot KOER code 31 first.

Code 31--R--(if no O code 31) Disconnect and plug the EGR vacuum line. Rerun KOER. Do you still have 31 or does it change to 32 & 34?

Code 41--R--Right O2 sensor sensing lean.

Code 91---R-- Left O2 sensor sensing lean.

Your car does not have HEGO (heated) O2 sensors. So single wire sensors are correct for your car.

Code 30--R-- not a valid error code. KOER test presents a 3 at the beginning of the test. This indicates the ECU is for a 6 cylinder engine. A code reader may present this as a 30. Just a guess. I have never used a code reader on these cars.

Codes 44 & 94 are Thermactor codes. This is the control for the smog pump air. Don't see how plugs could affect this.