Looking for some confirmation here...catalytic converter?

[TahoeInFC]

Thanks for the info! Looks like a good pressure test to step through. I wonder if AutoZone has a backpressure gauge in their loaner program. Will check up on this.

I was crawling around under the truck last night looking at swapping the sensors from bank 2 to bank 1. I didn't have the correct wrench (22mm, I think), so rather than booger them up with a 7/8" (which fit, but loosely) I decided to get the right tool and try again this weekend.

I DID learn during this exercise that the previous owner used Bosch O2 sensors in this thing about 20k miles ago. I'm not very pleased with this, as I've seen in post after post out here that Bosch sensors aren't the best choice for these rigs. Most of the people out here seem to agree that a guy should really stick with AC Delco or Denso, and avoid Bosch where possible.

So, my question for those interested...
After I do this test with swapping the rear sensors, depending on the results, I'm toying with buying four new AC Delco sensors and swapping them all.
If I do this, what's the difference between the AC Delco and the AC Delco "Professional" sensors? I see that Amazon and RockAuto both sell these flavors of AC sensors. The professional sensors are a little more expensive...are they worth it?

It may turn out that the O2 sensors have been getting slow on me, and my cats aren't at fault here. Would be nicer to spend about $150 rather than $450 with the converters.

 

[east302]

AC Delco sells, typically, three lines of parts. Advantage, Professional and OEM. The first two are most likely similar to what you would get at a parts store and may be sourced from the manufacturer that gave Delco the lowest bid. The guy at the factory in China takes a box of parts and slaps Duralast labels on some, Delco labels on the others.

Or, at least, that's how I gather the "Advantage" parts being labeled.

I would look for the ones that are marked AFS-105 and 106 (GM original equipment) at about $40/each.


Sent from my iPhone using Tapatalk

 

[TigerEyz3]

While I agree that it would be easier to replace the O2 sensors than to remove the old converters and weld in new converters, you're not looking at $450 to replace two converters. I think mine were ~$100/each (MagnaFlow).

 

[TahoeInFC]

While I agree that it would be easier to replace the O2 sensors than to remove the old converters and weld in new converters, you're not looking at $450 to replace two converters. I think mine were ~$100/each (MagnaFlow).

Well, I was adding it all up...
$200 for two converters
$100 labor for a local shop to weld them in for me (I can turn wrenches, but I don't weld)
$150 4 new O2 sensors
-------
$450

Some of the direct-fit cats are also around that $300 - $350 mark, so similar if I go that route with new sensors.

If I only have to replace the Bosch sensors (if they are at fault here), then I'm down to $150 if the current cats turn out to be OK.

 

[TahoeInFC]

Thanks east302

Yeah, those are the AC Delco sensors I was considering, but was just curious about the differences between their various quality grades. I appreciate the explanation.

A lot of great help out here!

 

[TahoeInFC]

Hey All,
I've been working on this thing from time to time, and have learned a few new things.

1) I swapped the downstream sensors from side to side, and the 'lazy' sensor from bank 2 (failing side) that hung around 0.2V seems to work better on bank 1, although only at idle. Holding at around 2000RPM it still slumps downward toward the lean end between 0.1V and 0.2V. Let off the throttle and at idle the sensor pops back up to around 0.7V bounces around a lot, and sort of settles mid-range. The sensor that was formerly in bank 1 is alive on bank 2, but moves around all over the place, sort of tracking the upstream sensor. This would seem to indicate a bad cat, as I was suspecting.

2) I rigged up a pressure gage to do the back-pressure test on the upstream sensor bungs. On bank 1, it never really exceeds around 1psi, even when I goose it a little. Low downstream pressure. Bank 2 makes the pressure gauge a lot more active and it moves around quite a bit. Still stays around 1psi or so at idle, but when I goose it, it jumps up to around 3psi or higher. Hard to tell because the needle bounces around a lot. Definitely higher than bank 1. Another indicator of a failing bank 2 cat. Also noticed a little soot on the O2 sensor. Nothing horrible, but indicates some rich fuel I think. Guessing it could have been rich because the downstream sensor was starting to get starved by the converter that may be partially plugged, making it read lean and trimming the engine to the rich side.

3) After swapping the downstream sensors and resetting the SES code this weekend, it threw another code today, same bank 2. Didn't follow the O2 sensor to bank 1. Bad cat on bank 2.

I think I have my answer. Sorry for leading everyone through this saga, but your help has been awesome in troubleshooting this issue. My thanks to you. I'm pretty conservative when troubleshooting, because I hate spending money if I don't have to. Hopefully all of this helps someone else in the same boat.

As earlier suggested, I think I'll go ahead and change the converters and put in some new AC Delco sensors to replace the not-so-old-but-possibly-lazy Bosch sensors.

Cheers

 

[TahoeInFC]

Hey All, just closing this one out...
Put on new cats (both banks) and O2 sensors (all four). Runs much better and doesn't throw codes. Smells cleaner also...O2 sensor signals look pretty solid.
I think it might still be running a tad rich, however, but that's an investigation for another post.

Thanks again for all your help!