O2 sensor, Knock sensor & 3100 Boost-pressure control

[steve30]

I have a single turbo with single bank o2 conversion. The car ran fine for a while but now its throwing a couple codes and "limp mode" 3100. The car runs fine when I cold start it but after a few minutes it shows the AFR fluctuating from 11-25 and the car has a slight jerk to it under light throttle. I know the first thing to do is replace the primary O2 and see if that solves the problem but I'm curious as to why the knock code shows up. The engine is fully built and closed deck so I use MHD's reduced knock sensitivity. I also have solid engine mounts and my tuner didn't see any issues with that. I'll definitely start with a new o2 and see if that solves it but I'm just starting this thread in case the issue is not resolved. Prior to the single bank conversion I ran the same o2 sensor so I'm thinking it did have some damage/overheating when it was being used on the turbo manifold (original doc race top mount which I've had no issues with). Thanks for your help in advance.

 

[steve30]

Update: I replaced the o2 and no more codes/limp mode. The previous O2 sensor was used on the old setup (before I converted to single bank) so I'm guessing it was on its way out anyways. Just curious if anyone knows, could a bad O2 cause a knock sensor code? I was being told that a bad knock sensor would throw off the O2/AFR's only, not the other way around.

 

[wheela]

Glad you got it sorted

If your O2 sensor is not working properly, you can run lean which can cause knock. So since your O2 sensor was bad, I imagine any knock or timing corrections you were having were real.

I don't see how a bad knock sensor could impact accuracy of your O2 sensor readings. Depending how bad the knock is, the DME may respond by richening the AFR to help stop the knock, is that maybe what they were talking about?

 

[steve30]

Glad you got it sorted

If your O2 sensor is not working properly, you can run lean which can cause knock. So since your O2 sensor was bad, I imagine any knock or timing corrections you were having were real.

I don't see how a bad knock sensor could impact accuracy of your O2 sensor readings. Depending how bad the knock is, the DME may respond by richening the AFR to help stop the knock, is that maybe what they were talking about?

I was searching the knock sensor code which is what MHD was showing (2E68 Knock-sensor signal 1) and most of the results lead to a faulty knock sensor or wire damage. I also had the specific P code for the knock sensor which was showing P0326.

What made me think to change the O2 sensor first was the fluctuating AFR. I was a little confused and maybe focusing too much on the bank 1 knock code because based on your explanation I would expect a single O2 conversion to trigger both knock sensors. Thankfully its resolved. I also did a few logs and no timing corrections across all cylinders.

 

[steve30]

Unfortunately the O2 code has come back again. No limp mode or knock code though.. I felt the stutter/jerk while under normal driving/light throttle and checked the AFR. As you can see in the log below during idle/light throttle it fluctuates.

datazap.me | Steve30 | O2 Code

datazap.me