Posted a related question in the Evo General post. Basically I am getting a P0134 code (o2 sensor not working) and then it's throwing a P0171 (system too lean) code because of it. We checked the logs, and the front o2 basically stays on 0.000, sometimes jumping to 0.020, and then back down to 0.000. In contrast, the rear o2 reads upwards of 0.9xx.

It is a telltale sign of a bad o2 sensor, but the weird thing is that we have tried 2 o2 sensors now, exact same findings. I am surprised that I would have tried 2 bad sensors, back to back.

The car is stock, with 280 HKS cams, and a manual boost controller set to 25 psi. Emery at STM tuned the stock PCM.

Are there any settings in the ECU that I should check that would cause symptoms like I mentioned above, or is it pretty much guaranteed to be a bad sensor? I read an old post about some periphery bits you can can change, but I don't think that would cause the log readings that I am getting.

Please advise.

-mark

 

Check FAA bit 14, FAA bit4, FAA bit 1, these should all be "1"

 

All 3 are set to 1.

I am starting to wonder if the ECU is not having the circuit warm up. I am going to test that next.

Thanks for the bit info.

 

no idea good luck with that problem

 

I have a datalog that shows the behavior of the front o2, if anyone wants to try to decipher it for me!

I had to make it a .txt file to upload, so just change it to .csv, and open it with EvoScan

 

Mark, your STFT(o2 feedback) is maxed out at +24 indicating that it is adding 24% fuel... but you are correct... the front O2 isn't doing crap... what is the wideband reading when it is idling? How long has the problem been going on?

 

I just got the car about a month ago, and I had STM put it back to stock. I got it running down there and it warmed up without a problem, and then Emery dyno and tuned it with a basic tune, but it still didn't throw the code. Then on the way home about 3 weeks ago, the light came on.

Yesterday, we swapped a different front o2 in, and it is doing the exact same thing. We are not sure if either o2 sensor is good though, they were both ones just laying around the shop.

-mark

 

I would check the O2 wiring harness. You might have a break or short.

 

I am not sure what the voltages should be, but I checked resistance between the white signal wire to the PCM, and the black ground wire to the battery negative, and both were 0.000 ohms, so that is good. The other two wires are voltages when you key-on, but I am not sure what they are supposed to be. I think they were at 12V and 6V on key on, but I am not 100% certain.

I also checked the continuity of the front o2 sensor, and only 2 of the wires shared continuity (the 2 black wires together had a resistance of 0.000 ohms). The other 2 wires shared no continuity with anything. I checked the second o2 sensor in question, and it had the exact same measurements.

 

make absolutely sure there is a good front O2 sensor installed or you will be chasing your tail... though you could just run full time open loop and not have to worry about the front O2... for the front O2 got to oxygensensors.com... get the walker plug and play...

 

I was looking at that, I may just order one up today. Is the Walker one alright? I know Denso and Bosch are the kings, but Walker is priced right.

 

I have had a walker in my car for about 2 years no issues...

 

Good to know! I'll order one up now then, and try it out. Thanks for the help so far

 

Rock Auto had an OE style Denso front o2 for $48 shipped

 

Did you fix the problem? I am having a similar issue