Looking for a bit of advice on helping pass my CO state emissions test.

I replaced my O2 sensors due to an intermittent P1158 code that progressed to 4 codes - P0138, P1138, P1193, and P1158. No fault codes since they were replaced a couple of weeks ago.
Cleaned MAF with CRC Mass Air Flow Sensor Cleaner
Replaced plugs - RN11YC4
Cleaned throttle body with Berryman B12 Chemtool
Ensured all vacuum hoses and ports were sound and clear of obstruction.
Cleaned engine oil separator and poured Sea Foam into the port to ensure it was clear.

After all of this I failed emissions due to high NOx.

HC GPM 0.1601 Limit of 1.0000
CO GPM 3.6791 Limit of 15.0000
NOx GPM 3.9373 Limit of 2.5000

One of my cats was rattling for a couple of weeks a while back after someone attempted to steal it, but the sound stopped at some point. They cut completely through the exhaust pipe exiting the cat and I had a muffler shop weld it back together.
I'm pretty sure I'm going to need new cats to pass the test, but I'm trying the test one more time after using Cataclean. Probably won't work, but it's worth a try to avoid replacing the cats.
CO adopted CA emissions standards and the muffler shops are telling me I have to purchase CARB complaint cats. Average estimate for new welded in CARB compliant cats is $2200. Sheesh.

Let me know if there's anything I overlooked. I need to get this corrected soon since my plates expire at the end of the month.

 

State Omissions ?

We don't need no stink'n state omissions

Come to NM we don't put up with that liberal crap - and I am at 7.500 feet

Thats higher than mile high if you are math challenged

 

It's hard to tell who's screwing you more, the criminals or the politicians. It'll only get worse, for Colorado.

 

Looks like the engine is running lean. NOx is caused by high combustion temps, that might be caused by lean. EGR works to lower combustion temps, but not part of Rover V-8 design. Double check the PCV for a clear flow path (in and out). If you have OBD II, check fuel trims (long and short, both banks). Check carefully for vacuum leaks. Cats burn up left over hydrocarbons, but yours are very low already, so new cats might not help.

I just scanned an article that is worth a read: search High NOx Readings and Causes! by discountconverter.com. It mentions cooling system problems, among others.

 

Hi John, thanks for the reply!

The PCV (engine oil separator and port) is clean and I removed the hose and cleaned it with carb cleaner. It actually wasn't very dirty, but it's squeaky clean now. I've cleaned all the vacuum hoses and ports. I also removed and inspected the air intake hose between the MAF and throttle body, but it seems to be sound.

I've noticed recently that there is extreme vacuum when I remove the gas cap during fill up on occasion, and on other fill ups there is no vacuum at all. Some days the vacuum is so strong after a longer drive, I can actually hear a high pitched noise from the fuel cap. I ordered the replacement purge valve recommended in past forum posts (Vapor Canister Purge Solenoid Control Valve Hyundai/Kia) from Amazon since the OE part is no longer available.

Could that be failing and allowing too much air into the intake post MAF?

 

I'll check the fuel trims today. Engine temps aren't an issue as I usually run around 178-180 at speed and around 186-190 during long periods of rest or in slow moving traffic.

 

Some air hissing when removing the fuel cap, especially after a longer drive, is normal and indicates a tight system.

 

All of my vehicles have a little hiss, but this seems abnormal. I'll see if I can snag a video the next time I hear the cap singing. I can literally hear it from the driver's seat when I turn of the truck.

 

I think the gas cap hiss is supposed to be from releasing pressure, not vacuum. I never really thought about how air gets into the gas tank. I know I smell fumes when I open the cap with a woosh.

I would cap off the port from the charcoal canister at the intake plenum to see if that eliminates the vacuum on the gas tank. Maybe that will be enough to lower your NOx and pass the test. Do you know a shop with an exhaust gas analyzer?

The canister also has a port to atmosphere, that could look like a vacuum leak if the solenoid valve failed. I guess air might leak in to the purge canister system through the gas tank, if there is a path (e.g. fuel pump seat, vent tube, gas cap). The vent tubes on both my trucks were all cracked and leaking when I bought them, very common failure. But if the vent tube fails, the tank will not hold pressure or vacuum.

 

Fuel trims at speed are:
LTFT 1
-18.8%
LTFT 2
-18.8%
STFT 2
-3.1%

Cold idle fuel trims are:
LTFT 1
-16.4%
LTFT 2
-16.4%
STFT 2
10.2%

Online research states the MAF or coil could be going bad. Any input on how to correct this is appreciated. I've noticed lately on startup that the exhaust smells like unburned fuel.

Was going to plug the charcoal port on the plenum from the canister to see if that affects anything, but in the parking lot at King Soopers earlier today the expansion tank decided to burst. Just my luck! I replaced the expansion tank cap a few weeks ago because the old one was no longer sealing correctly. The extra pressure from a working cap must have stressed it too much. The original black tank was last replaced with a translucent version around 5 years ago, so it was about time for it to fail. I ordered a new translucent replacement, but it won't deliver for a week or so.
Had old Indy towed home to make sure no one steals the catalytic convertors.