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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.
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.
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).
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.
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).
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.
03-14-2019, 09:49 PM
