2nd Gen S-series (1995-2005) Tech Discuss 2nd generation s-series (1995-2005) general tech topics here.

P0420

  #21  
Old 03-14-2019, 09:49 PM
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Originally Posted by LesMyer View Post
Here's a video of what you will be doing. This guy's scan rate for his equipment kind of sucks, but you get the idea. The front sensor cycles and the other doesn't so much.

Hey it would be useful and very interesting to post before/after plots of the O2 sensor voltages on the same vehicle (if you end up installing the new cat)! Then people can see exactly how to do the diagnosis.

https://www.youtube.com/watch?v=KGpMzdEO5KY
Here is before changing the cat, red is upstream, green downstream.
Don't know if this is what you were looking for.

I'll do it again either tomorrow or saturday when I change them out

 
  #22  
Old 03-15-2019, 05:31 AM
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You want to plot B1S1 (an upstream) and B1S2 (post-cat) - not B1S1 and B2S1 (both upstream sensors). But otherwise a nice job on the plot!

Scan rate on your Torque Pro seems a bit slow (around 5/sec) and parts of the sensor cycles get missed - but it will work well as-is for this purpose. However there is a setting/option in Torque somewhere that speeds things up, as well as a scan rate monitor. I usually get around 25 data points per second on my 2001 with Torque Pro. Blazers before 2000 seem to be slightly slower, but yours should be similar to mine if you are using the BAFX OBD2 adapter.
 

Last edited by LesMyer; 03-15-2019 at 05:51 AM.
  #23  
Old 03-15-2019, 08:40 AM
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Originally Posted by LesMyer View Post
You want to plot B1S1 (an upstream) and B1S2 (post-cat) - not B1S1 and B2S1 (both upstream sensors). But otherwise a nice job on the plot!

Scan rate on your Torque Pro seems a bit slow (around 5/sec) and parts of the sensor cycles get missed - but it will work well as-is for this purpose. However there is a setting/option in Torque somewhere that speeds things up, as well as a scan rate monitor. I usually get around 25 data points per second on my 2001 with Torque Pro. Blazers before 2000 seem to be slightly slower, but yours should be similar to mine if you are using the BAFX OBD2 adapter.
I'll re-run it with those two sensors, I'm using the same adapter (BAFX OBDII).
 
  #24  
Old 03-15-2019, 09:06 AM
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Originally Posted by FUN-V View Post
I'll re-run it with those two sensors, I'm using the same adapter (BAFX OBDII).
Great, glad we caught it before you removed the cat.

For the speed, make sure faster communication is checked in OBD2 adapter settings.
 

Last edited by LesMyer; 03-15-2019 at 09:12 AM.
  #25  
Old 03-15-2019, 10:04 AM
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  #26  
Old 03-15-2019, 10:13 AM
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Yep, cat is junk! Cycle is significant and cycle timing is the same frequency as pre-cat. Replace away with confidence!! I think it's a pretty cool way to check a catalytic converter. It's really how the PCM checks it.

Also looks like your scan rate has dramatically improved here - now 25 or so scans/sec (counting the data points in the plots). I believe the scan rate is displayed as a choice under OBD2 adapter screen, once connection has been made.

CONDITIONS FOR SETTING THE DTC
The VCM determined that the oxygen storage capacity of the catalyst has degraded below a calibrated threshold.

Oxygen should be retained in the converter and then slowly released - so post cat O2 shouldn't fluctuate like seen with front sensor - should average out. Yours is retaining a little O2 so cycling is less severe, but PCM recognizes degraded performance and turns on the light with the PO420.

So now will be interesting to have the same plot with a new cat. I'll plot mine too and post it as a good original cat that has seen 100K miles.
 

Last edited by LesMyer; 03-15-2019 at 10:42 AM.
  #27  
Old 03-16-2019, 12:25 PM
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Originally Posted by LesMyer View Post
Yep, cat is junk! Cycle is significant and cycle timing is the same frequency as pre-cat. Replace away with confidence!! I think it's a pretty cool way to check a catalytic converter. It's really how the PCM checks it.

Also looks like your scan rate has dramatically improved here - now 25 or so scans/sec (counting the data points in the plots). I believe the scan rate is displayed as a choice under OBD2 adapter screen, once connection has been made.

CONDITIONS FOR SETTING THE DTC
The VCM determined that the oxygen storage capacity of the catalyst has degraded below a calibrated threshold.

Oxygen should be retained in the converter and then slowly released - so post cat O2 shouldn't fluctuate like seen with front sensor - should average out. Yours is retaining a little O2 so cycling is less severe, but PCM recognizes degraded performance and turns on the light with the PO420.

So now will be interesting to have the same plot with a new cat. I'll plot mine too and post it as a good original cat that has seen 100K miles.
So here is the same graph, same sensors after the new cats were installed (both front and rear cats).

 
  #28  
Old 03-16-2019, 06:17 PM
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Originally Posted by FUN-V View Post
So here is the same graph, same sensors after the new cats were installed (both front and rear cats).
Excellent work!!! It's times like this that makes this forum worthwhile. Now everyone can stop guessing if their cat is good or bad!!
 

Last edited by LesMyer; 03-16-2019 at 07:39 PM.
  #29  
Old 03-16-2019, 07:12 PM
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Here's mine @ 2000 RPM in park. Good original cat at 100k miles
Edit: 3/25/19 Seems that test in post #43 may be a better way to determining if cat is good or bad. Here post-cat O2 sensor is maxed out rich for some reason - that may invalidate what I was trying to show.
 

Last edited by LesMyer; 03-25-2019 at 07:21 AM.
  #30  
Old 03-16-2019, 09:24 PM
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wrong pic
 

Last edited by FUN-V; 03-16-2019 at 10:23 PM. Reason: wrong pic

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