Emissions Question

[Texas Jimmy]

Hi y'all...I used to hang out here a lot, but now I just lurk now and then.

I've got a TBI crate motor, 3 yrs old, with about 23K on it. Mobil1 and M1 filter since new. All new sensors (Delco) and vacuum lines when I did the swap. Just went for the sniffer test and for the first time it failed. I haven't touched a thing since new.

Everything passes well within limits except NOx at low speed. The standard is 1465, I hit 2027.

High speed (25mph) 1767rpm Low speed (15mph) 1335rpm
standard current standard current
HC 142 79 PASS 145 106 PASS
CO 1.74 0.34 PASS 1.30 0.27 PASS
CO2 13.2 PASS 14.6 PASS
O2 2.5 PASS 0.6 PASS
NOx 1362 1192 PASS 1465 2027 FAIL
Dilution >6 13.5 >6 14.9

I have the timing advanced +4, new Delco O2, 195 Tstat, and EGR (did it too)seems ok.

If I am reading correctly from the site I bookmarked (from here), would you agree that I should be able to clear this by just returning the timing to 0?

If I fail this, I have to jump thru some stupid hoops to show how much I spent fixing it and then pay another $32.50 or whatever to redo it.

The truck runs very strong, smooth and reliably.

Thanks.

this thing edits out the spaces in the stats makes them a bit harder to read

 

[chevyuser74]

egr and the catylitic convertor are the big players in nox, my bet is on the cat, with it failing at an idle, because the egr isnt in play at that point.

 

[Jason4x4]

was the truck warmed up? if not, the cat might not have been working very effiecient.

 

[kevin400ex]

what they said above, and retarding the timing will reduce the nox as well.

a trick to help reduce the nox is to clean the carbon out of the combustion chambers. it involves getting the engine hot and holding it an an elevated rpm and slowly drizzling some water into the throttle body. the water knocks the hot carbon off sending it out the exhaust (hopefully) some shops will try and sell a decarbonizing procedure to cutomers that failed nox test, and this is basically what it it.

 

[Texas Jimmy]

The EGR was done when I did the swap. I also cleaned everything I could while it was apart. I pulled a couple plugs and they are clean as a Safeway chicken. With this few miles on the engine, I would guess carbon wouldn't be a major player. The Hi Flo cats are about 12 years old, so as much as I hate to face it, if retarding the timing doesn't get me by, I guess I was wanting new cats anyway.

The engine was plenty warm as I had just made a freeway run and didn't have to wait at the inspection station. I rarely drive this truck on short trips just piddling around town.

Thanks for the quick replies. Hopefully I can get this taken care of within the next 15 days.

 

[chevyuser74]

a different way to get rid of the carbon is with a can of sea foam, get the engine warm, pull off a vacuum line and stick it in the can and drain it out, word of caution do this outside, its going to smoke real bad, also one of the benefits, drive around the block and see if u can cover the block in smoke.