Toyota Repair: Toyota 22RE Check Engine Light, air fuel ratio, toyota 22re

Question
Hello,
The problem is on my 1987 Toyota 4-Runner 4x4 5-speed 22RE fuel injected, 150,000 original miles, 5,000 on new overhaul.
The problem started after I installed a header made by Pace Setter.  The original location for the O2 sensor is on the exhaust manifold close to the head.  The new location for the O2 sensor is behind the header collector under the cab.  I extended the sensor wire with similar sized wire.   Now the check engine light comes on intermittently.  It only comes on when I am traveling at a constant speed when the revs are above 2500 rpm.  If I let off the throttle, the light turns off after a second or so.  When I get back on the throttle the light will come back on after 10 to 20 minuets.   The light has never come on while idling.  Also, sometimes it will idle at about 1500 RPM, sometimes the idle will be so low it stalls, other times it will fluctuate, sometimes it will idle fine.  I installed a new O2 sensor and it didn't change anything.   I read the stored code and it gave me 5 flashes.  I looked it up in Chilton and the explanation is "Oxygen sensor signal-sufficient feedback but oxygen sensor signal unchanged".  I have noticed an large increase in fuel consumption.  If you need any more info, please let me know.   Thank You.


Answer
Welp, one of three things.
1) The new oxygen sensor is faulty too.
2) Your wiring is defaulty
3) You aint do it right! Ya moved the sensor too far down the pipes.
One wire oxygen sensors rely on the high combustion temps to keep the sensor heated. They are not externally heated by the computer to stay around 500-700*F.

What happens, is that the sensor won't stay hot enough to output the signal swing the ECU expects to see. (About .44v to .46v)





The fuel consumption is excessive because you're in open-loop. No oxygen sensor keeping the engine bouncing "around" a 14.5:1 air/fuel ratio. Instead it's running in a small fail-safe, and *probably* running more around 11.5-13.5:1 A/F ratio (Which is richer, i.e. more fuel).







Hook a multi-meter up to the sensor, and chekc the voltage output. It should stay right around .45v all the time by the time the engine is warm.

See, the signal has to swing. This isn't the 22r-e specification (It's for another i4 obd-I toyota engine). But you will normally trip the code when:
The signal stays at .45v at >1,500rpm after two minutes. (Dead o2 sensor responce)


Since you replaced the sensor, and have the same code. I'm guessing that your extension doesn't work, or the o2 sensor is simply way too far away from the exhaust ports on the head.