Charting O2 Sensor Voltage - Let's Beat the P0420!

In an effort to avoid the P0240 CEL without software .... Lots of us are running an O2 sensor spacer (various brands), spark plug non-foulers, and some are even running a custom combination. Some are successful, some aren't.

In essence, we're all trying to figure out what voltage, or voltage differential, the ECU wants to see at sensors 2 and 3. Beyond trial and error, I'd love to solve this mystery using actual data. It may be our only hope.

Below is a chart of voltage at Bank1 Sensor2 and Bank1 Sensor3 during my morning commute. I grabbed 5 minutes of data towards the end of the drive. Ambient temp around 48F. First 20% or so is freeway, the rest surface streets b/w 0-50mph.

As you can see, the differential can be quite dramatic. My suspicion is that the Stratmosphere spacer is actually causing the sensor to read TOO lean, triggering the P0420. I also get an intermittent P2275 (O2 Sensor Signal Stuck Rich bank1 Sensor3), so go figure.

This all leads me to believe we have to hit a sweet spot between too dirty and too clean.

PLEASE post your own logs in this thread along with your spacer setup. I'll be swapping in a different sensor soon, and I plan to post back with a new log for comparison. Maybe we can solve this together :w00t:

Without further ado, the data:

My setup:

• 2012 CC 2.0T CBFA
• GIAC tuned
• 3" catted downpipe (200 cell metal)
• No spacer on sensor 2
• Stratmosphere 90deg spacer on sensor 3

Click here for full size, new window.

What specific fault codes are you wanting info about?

DBESTGTI said:

What specific fault codes are you wanting info about?

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P0420. That's the one that haunts me.

Like I explained above, it sounds like we have to hit some sort of a voltage sweet spot to avoid that CEL with a HFC or no cat. If we figure this out, 1/4 of the threads on this board will be obsolete.

I have an intermittent P2275 with the current spacer, but I'm not sure how it's related.

Are you only wanting CBFA logs? My CCTA only has the 1 O2 sensor after the cat and the 42DD spacer took care of that code fortunately.

smrtypants44 said:

Are you only wanting CBFA logs? My CCTA only has the 1 O2 sensor after the cat and the 42DD spacer took care of that code fortunately.

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Thanks, yes the CBFA is a whole different animal. Way more picky.

Wow. Crickets.

C'mon ... if you've got a spacer or two installed, do some logging on your way home from work tonight and post it up!

I'm still stock (2,900 miles) but also noticed none of the dp cheats work for the cbfa engines. I'm very interested to see any results from logging. You may also want to see what a stock dp log looks like compared to an aftermarket. Also specs of what a good stock set would read should help figure out what your aiming for.

Dirty Harry said:

specs of what a good stock set would read should help figure out what your aiming for.

Click to expand...

Of course, why didn't I think of that? Someone with stock downpipe please log this and post up!

Good thing you asked for that before this weekend....stock DP is hopefully coming off this weekend. LOL

I will run some logs tomorrow on the stock DP and post them up.

Thumper said:

Good thing you asked for that before this weekend....stock DP is hopefully coming off this weekend. LOL

I will run some logs tomorrow on the stock DP and post them up.

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:thumbup:

EDIT: LOGS ARE BEING CORRECTED FOR MISALIGNED DATA


OK, here we go.

I logged the cat temperature too, just to have it, but it screws up the graph. Still, I have the data for reference if we need it.

I logged data at idle, over the normal driving to the test area, and then did 3 test runs following the APR format with 3rd gear pulls from 2000 to 6500 RPM. Next time I am going to have to do 2nd gear, because 6500 in 3rd gear is 80mph........




STARTUP AND IDLE





NORMAL DRIVING




TEST RUN #1




TEST RUN #2




TEST RUN #3






Those are some interesting results, with very different results between all 3 runs. This may not be as easy as we hoped. LOL

Stock DP is staying on for now due to time issues, at least until next weekend. If we need more log runs I can get them done. I plan to go to Napa next weekend, I'll log the entire trip (4+ hours) if we think that would help.

Thumper you totally rock.

I notice from looking at your normal driving graph that your voltage at sensor 3 doesn't really go below .2. If you look at mine I dip to almost 0.

Would lower voltage signal leaner conditions? This would back up my theory that my current spacer has pulled the sensor too far out of the stream.

More later ..... this is good stuff!

poprocks01 said:

Would lower voltage signal leaner conditions? This would back up my theory that my current spacer has pulled the sensor too far out of the stream.

Click to expand...

That was my assumption at first, but this does not make much sense as in all my graphs sensor 3 is often consistently reading higher voltage than sensor 2. I think we need someone that understands the electrical working of the O2 systems better to chime in. But if sensor 3 is AFTER the cat, then it stands to reason it will be reading much cleaner than sensor 2. With that basis, on my stock setup, it appears that higher voltage signals a cleaner burn in sensor 3. It has been a long time since high school where I studied electronics, but voltage should increase as resistance decreases......if the sensors are designed to open the circuit as they sense LESS gases than that would explain the higher voltage. However, the spikes and vast variations in the charts still don't make sense totally to me.

Again, on my normal drive sensor 2 hits 0 near the end, and as you mention, sensor 3 never gets close.

However, noting that your sensor 3 DOES go to 0 where mine does not, it's a good first step in charting the differences.

Decided to do a longer run to capture as much data as possible since my DP install has been delayed once again.

I was thinking, since the CEL does not appear immediately it is likely triggered by too many out of tolerance readings over that period of time rather than a constant out of tolerance reading.

So, here is about 30 minutes of data. I have the full log even though it's a lot to display at once, and then I broke it into smaller chunks of 500 lines of readings. Finally there is a smaller 300 line sample at a point where RPMs were varying more.






































This is going to take a lot of experimentation and we are going to need to test with individual spacers and pull out the effect they have on the readings. Lots of trial and error.

Wow. So, with a stock setup sensor 3 has a HIGHER voltage than sensor 2. For contrast, if you look at my original log, sensor 3 is averaging .1V LOWER than sensor 2.

So potentially the hi-flow cat creates a situation where the voltage is so different that they're actually swapped?

According to Wikipedia, more oxygen = lower voltage, as oxygen is a poor conductor. Running rich will deplete oxygen creating higher voltage reading. Lean, lower voltage as there is excess oxygen. Not sure if/how this helps us, but them are the facts.