Help with CA Smog Check; P0420 and High Emissions

[mkodama]

So I'm failing smog with an otherwise great driving van. It's a 1997 Chevrolet Astro. The van failed with two codes, high emissions values across the range with the 15mph nitrous oxides value being beyond the limit, and a check engine bulb light was out.

I'll start off with my smog results from a few weeks ago:



-Check engine light was an easy fix, replace the bulb in the cluster, and no problem.
-The P0446 is likely the purge valve. That's been replaced, and I'm just waiting on the readiness monitor for EVAP to clear. No code has come back yet.
-The P0420 Cat Efficiency Below Threshold, and the associated high emissions test is what I need help with.

The first thing I did was get something so that I can see what the fuel trim values were, to see if there were any crazy vacuum leaks or what not. Conveniently the wifi OBD2 reader I bought also shows me codes and readiness monitors and allows me to to reset, which was also needed in my quests to pass smog.

At idle:


At 2500 rpm:


Everything looked pretty normal, and the oxygen sensor voltages were bouncing back and forth like they should, but the thing that stood out was that Long Term fuel trim was double digit negative values at idle, and these would lessen at high loads. According to what I read online:

Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.

The leaky injector part stood out since the issue was worse at idle, where the small amount of leaking fuel would make the biggest difference. To deal with this, I did the central sequential fuel injection to multiport sequential fuel injection conversion, and this also included a new fuel pressure regulator, and I got to replace a few gaskets that might be leaking as well.

After dealing with a throttle position sensor and idle control valve that started acting up after the conversion, the van runs great; better than before. It's smoother and quieter than it was before, and fuel trims are significantly better looking now. Long term fuel trim is -3.7% at idle, +3.1 under low to moderate throttle, and +7% under heavy throttle. Not perfect, but nothing terrible and much closer to what everything should be. Mostly within the realm of what minor vacuum leaks would cause.

Everything was looking good, mot of the readiness monitors were about to complete, and the P0420 came back...

I'm really thinking it's a catalytic converter at this point, so I started taking out the catalytic converter section today, and I got nothing but frustration. It looked like it's been replaced before, since there were two difference sizes of nuts holding the section to the manifolds and exhaust, and an odd weld int he middle of one pipe. One of the the nuts attaching it to the rear section was so badly seized that I twisted the stud into two pieces during removal, great. So after struggling to get the catalytic converter section out, I then proceed to remove the oxygen sensors; two out of four tear out the threads on their way out, excellent!

Now here is the part that really did it for me, the catalyst material inside looks brand new, and I can't tell if the oxygen sensors are normal, or if they are fouled. They all have a whitish coating, which seems like the pictures I've seen of either coolant or silicone contamination. They all have white on them, aside from the pre-cat sensor, which just has minimal amounts.









So... Any ideas?

[paulo57509]

Here's my take on what you have (not an expert opinion by any stretch).

High NOx can be caused by (not necessarily in order):

1. Lean mixture
2. High combustion chamber temperatures
3. Vacuum leaks (causing lean mixture)
4. Inoperative or marginally operating EGR

If you're going to fail NOx, it'll fail at 15MPH all the time.

I think we can rule out lean mixture and it's causes. If you look at the O2 readings, there's very little left over oxygen showing up. If your mixture was lean the O2 numbers would read much higher.

As a side note, your HC numbers are way low so rich mixture shouldn't be a concern. This also means that the portion of the cat that handles HC (reduction or oxidation??...can't recall) is working. Going out on a limb here, but I'd say your cat is fine.

If you have an EGR, I'd look into it's operation and if the exhaust passages might be plugged. Start the engine and lift the valve diaphram with your fingers (on a cold engine and if you can get to the EGR valve). If the engine dies, the passages should be clear.

In order to get rid of the P0420 and since you already have the O2 sensors out (and some have trashed threads anyway), I'd just replace them all.

[mkodama]

Thanks paulo57509,

Good information and ideas. The engines does have exhaust gas recirculation so I'll definitely look into that.

[mkodama]

-I removed the exhaust gas circulation tube and it was fine. Simply a metal tube with insulation around the outside, and air could easily pass through it.

-The exhaust gas recirculation valve on the other hand was a bit gunked up. I'm not sure how you are supposed to test an electronic EGR valve, so I simply replaced it with a new unit from O'reilly's. Pricey at $130, but lifetime warranty. Even though it came with a gasket, I opted to get the Dorman Help! brand gasket with the filter screen, as a precaution. The old gasket came apart during removal.

-Upon second inspection of the catalytic converter section, one of the converter elements was loose. In combination with the loose element and 3 out of 4 damaged oxygen sensor bungs anyway, I opted to get an entirely new direct fit, CARB compliant unit from Magnaflow. So far I highly recommend Crazy Boy Auto if you need to buy one. I got the converter for $500 shipped and they really did ship out the unit within 24 hours as advertised. Fedex tracking info says I should have the unit by tomorrow.

-I decided to take apart the old catalytic converter for some pictures and learning. The first section(left) is for turning nitrous oxides into nitrogen and oxygen, the second section(right and cone shaped) is for turning hydrocarbons into water and carbon monoxide into carbon dioxide. The second section was missing the packing that holds it in place, so it was allowing it to move around and allowing gas to go around the outside edges. Also notice how hot and how clean the working section made the walls of the converter.











And kinda unrelated, but here's a fun video I recorded of running the van without an exhaust. It certainly has a sound similar to an American V8 and quite a bit different than a Japanese V6.

http://youtu.be/MpF6aZ34pCU

[mkodama]

How do you get the evaporative readiness monitor to complete? I've been following the GM driving cycle and as well as daily driving the van, and still not ready, while everything else is good. It's the only thing holding me back from a smog retest.

Also, the van has been running great lately. This maintenance has felt like it's definitely brought back a little power, and a lot of smoothness.

[mkodama]

Success!

Well, close enough. Just had a pre-test done and all the values are better than average. No measurable CO, no measurable unused O2, hydrocarbons are half of the average, and nitrous oxides, which were what failed me before, only a quarter of the average.

CO2 stayed nearly identical.

The EVAP readiness monitor still hasn't cleared, but up to 2 incomplete monitors are allowed for 1996-2000 vehicles.

Now just to get the real test completed.

[97cargocrawler]

How do you get the evaporative readiness monitor to complete? I've been following the GM driving cycle and as well as daily driving the van, and still not ready, while everything else is good. It's the only thing holding me back from a smog retest.

Also, the van has been running great lately. This maintenance has felt like it's definitely brought back a little power, and a lot of smoothness.

It's never a good idea to reset those monitors unless you're doing it like a week before the test. They don't all need to have completed either. My Smog tech told me that you can have several pending monitors depending on the year of the vehicle. I think he said I could have two pending tests with my 97. I waited a week to get mine to clear and I was a week into expired reg. Then I found out it would have passed with that monitor pending.

If the evap has an issue they find it when they pressurize the tank with nitrogen.

[markmitch]

OK so I am moving to California the 25th and I have a question: I was told a garage has to do the cat converter swap but mkodama you said you did yours? is that legal in Cali? I am just asking because my van has no converter and I know I have to get one and it would be great if I can do it myself, Thanks

[mkodama]

It's never a good idea to reset those monitors unless you're doing it like a week before the test. They don't all need to have completed either. My Smog tech told me that you can have several pending monitors depending on the year of the vehicle. I think he said I could have two pending tests with my 97. I waited a week to get mine to clear and I was a week into expired reg. Then I found out it would have passed with that monitor pending.

If the evap has an issue they find it when they pressurize the tank with nitrogen.

All of that was covered in the post above you. No pressurizing of the tank was observed during the smog check today.

[mkodama]

OK so I am moving to California the 25th and I have a question: I was told a garage has to do the cat converter swap but mkodama you said you did yours? is that legal in Cali? I am just asking because my van has no converter and I know I have to get one and it would be great if I can do it myself, Thanks

I have no clue on the legality, but I never even saw the technician look under the car. If he did, he would have seen a catalytic converter with a California Exemption Order number on it. I even told him that I replaced the cat, and he knew it had previously failed smog when he entered my Astro's info, and there was no issue. This was at a Star approved smog check station as well.

[paulo57509]

OK so I am moving to California the 25th and I have a question: I was told a garage has to do the cat converter swap but mkodama you said you did yours? is that legal in Cali? I am just asking because my van has no converter and I know I have to get one and it would be great if I can do it myself, Thanks

I have no clue on the legality, but I never even saw the technician look under the car. If he did, he would have seen a catalytic converter with a California Exemption Order number on it. I even told him that I replaced the cat, and he knew it had previously failed smog when I entered my info, and there was no issue. This was at a Star approved smog check station as well.

Just thinking out loud here.....

I would install the converter(s) before bringing the vehicle to CA. Once here, I doubt the test station is going to grill you on its history. How would they know you've been illegal before you showed up here? All they know is it came from out of state. So it wouldn't need to have CARB certified cats even if they were "replaced" (wink-wink)

I brought my Acura Legend into CA from Washington state. Had it tested in CA with no issue. Drove it down to the DMV. The girl looked under the hood for a minute or two. I paid my fees and she handed me the registration papers, sticker, temporary title and new plates.

I have seen a test station tech look for the CARB cert on my replacement converter on another vehicle I own. This was at a test station that I have been going to for the past 10 years. But this was for a re-test because it had failed two weeks prior. I also overheard him on the phone reciting my vehicle VIN and the CARB number that was stamped on the converter. I don't think they would bother if CA records show no previous test failure. I think it's a hit or miss thing.