Another Colorado Emissions Failure

[dubyehnel]

Hi Folks - any help in guiding me in the right direction for a diagnosis would be much appreciated. I've got a combo of NOx and CO that are over the limit. The print outs are attached. Based on what I've read I'm thinking it may be the cats, but just wanted to check before dropping some serious $$$.

Side piece of info - A few months back right after I drove the LC out to Colorado from Georgia I threw a po420 code, but I cleared it and it never came back.

 

[ChiTown]

Clean all your egr passages, check the vacuum modulator and vsv for the egr valve.
After the egr is functional grab a bottle of cataclean from the parts store dump it in on a 1/4 full fuel tank. Get the truck nice and hot and had to the emissions test station.

 

[landtank]

One of my first things to do is have the injectors cleaned. Always seems to help.

 

[DHwreckage]

I just went throught he same problem with CO emissions and passes this past saturday. heres a link to my thread with good advice and there are a few links in there to a good testing procedure for the EGR system. i was throwing a P0401(every 100 miles or so) and PO420 (happened once). heres a link: https://forum.ih8mud.com/threads/failed-emissions-high-nox.798086/

 

[Pin_Head]

Besides the high NOx and CO, you are close to failing HC, so you may have more than 1 problem. If it is a high mileage truck, I would start with a compression test to make sure it is worth fooling with.

 

[landtoy80]

http://www.obd-codes.com/p0420 cat.
From my experience trying to pass CO emissions you most likely have to buy new cats to pass the newer lower limits. Being that you threw a cat code in the past, thats a good sign you need new cat(s).

If you spend more than $715 you can apply for a waiver as there is a $715 spending limit. I started the process after spending over $715 but gave up as I moved to western CO. You have to make an appointment and bring in you car to be checked by their mechanics to see if they can get you to pass.

You can go to a shop and have them diagnose the problem (that $$$ goes toward your $715 spending cap). Do a search, there was a place in Aurora a few years back that did a goo job for one 80 owner having problems passing test.

When I replaced the O2's, EGR modulator and VSV I got very close to passing and I only had to get to 4.0 NOx. You need to get to 3.5 . I cleaned the injectors and decarboned the motor with several cleaners and it did help but not much.

You have a OBD2 setup so if you had a scanner like a UltraGauge or ScanGauge you can see what is happening in real time as you drive. Not sure if buying one of them would go towards fixing your spending cap, you might want to check with Air Colorado and see.

 

[ToothDr]

http://www.obd-codes.com/p0420 cat.
From my experience trying to pass CO emissions you most likely have to buy new cats to pass the newer lower limits. Being that you threw a cat code in the past, thats a good sign you need new cat(s) QUOTE]


I agree. I replaced both my cats and both O2 sensors. Passed denver emissions with no problem . I had high NOx issues. Sounds like may have multiple issues. X2on the compression test.