Replaced cat in March 2011 to pass emissions here in Colorado. Tranny went in April...rebuilt it and put her back together. Had to cut the exhaust to get the trans back in, and used clamps to put the pipe back together.

Fast forward to March 2013. Failed emissions again with the following numbers:

HC GPM: 2.4647 (limit 1.2) FAIL
CO GPM: 44.5889 (limit 15.0000) FAIL
CO2 GPM: 702.9656 (not regulated) N/A
NOx GPM: 4.4538 (limit 2.5000) FAIL

Replaced plugs and wires. Upstream O2 was replaced about a month before the emissions test fail after it tripped CEL. Took it into a shop and they replaced the cat (said it was dirty but not melted) and welded up the exhaust so no more leaks pre-cat.

Emissions re-tested today- made sure cat was good and hot. Failed again with the following numbers:

HC GPM: 2.1700 (limit 1.2) FAIL
CO GPM: 29.9798 (limit 15.0000) FAIL
CO2 GPM: 802.9723 (not regulated) N/A
NOx GPM: 1.5972 (limit 2.5000) PASS

Already dumped $500+ into getting her to pass. Can't spend a lot more on diagnosis. Any thoughts?

Could the downstream O2 sensor impact these numbers?

Thanks in advance for your advice!

 

I've read that you should replace both O2 sensors at the same time.

SJ02

 

the downstream o2 sensor does NOTHING EXCEPT MONITOR THE CAT will not affect the way that the truck runs

 

This is what I've heard, which is why I only replaced the one triggering the CEL.

Any other ideas on what I should replace?