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High NOx, '97 2.4L Buick Skylark

ramack

ramack

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Centennial, CO
I need help with a non-Blazer issue happening with my daughter's '97 Buick Skylark. It has a 4cyl LD9 which I rebuilt the top end 12/2021. It had blown the head gasket, gotten hot and warped the head. I had the head milled flat, valve job, timing chain, water pump. Basically anything I had to take off was replaced. This engine had to be the biggest PITA to work on, but it's been running great since, no issues...until yesterday. She needed to get it smog'd for Colorado registration that expires next month.

The engine light was on, which hadn't been on after the rebuild. Unsure when it came on, my daughter claims it's always been on (false). My OBD reader won't connect to the ECM, but Advance Auto was able to pull P0404 for a code. I tightened the gas cap and was able to clear the code, the engine light went off and has stayed off.

We took got it smog'd and it failed the test. High NOx failure., CO and HC were higher than the 2020 smog test, but well below the limits.

2022 test results
1658928852702.png

2020 test results
1658928959039.png

Really I'm looking for what to start looking for. This morning, I'm going to look for vacuum leaks. From Googling, possibly causes for high NOx are engine running hot, bad O2 sensor or bad cat. converter or some reason for lean mixture. I'd rather not shotgun it and just start replacing the least costly parts first and retest, but that's about all I can do, short of taking it to a shop.

Any ideas as to where to start looking?

Thanks
 
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The above is from Rock Auto. Looks like Colorado has now been Californicated. Crap the "legal" cat is ~$350, the EPA cat is $175.
 
I Googled and found how to do a thermo test on cats. The outlet temp is lower than the inlet temp, so it's definitely bad. To do a test on a good cat, I did the same type of thermal test on my '79 K5, the outlet is 300F higher.
 
I was going to suggest the cat test. But you seem to have gotten to that.

The pass numbers were greatly reduced on the report. It would have passed if the old numbers applied. So glad I am not around that area.
 
ktmoutfront said:
I was going to suggest the cat test. But you seem to have gotten to that.

The pass numbers were greatly reduced on the report. It would have passed if the old numbers applied. So glad I am not around that area.
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Yeah, I noticed the decreased limit levels when I got home that evening and compared the previous (2020) test. I went back to the emissions test yesterday to ask if it was a typo and he said no. Beginning 2022, Colorado now has the same standards as CA. The price for a replacement cat almost doubles. I've got parts coming from Rock Auto, tried to order the EPA cat, but they wouldn't let me. So I've got the CARB cat coming instead.

From the info below (Rock Auto), looks like NY and ME are next to be Californicated.
1659026245694.png
 
Your governor said, the night he was elected, "I want to make Colorado just like California". Wife and I looked at each other and decided to get out.
 
ktmoutfront said:
Your governor said, the night he was elected, "I want to make Colorado just like California". Wife and I looked at each other and decided to get out.
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He isn't my governor, but is Colorado's, ha. I do know what you mean though. I'm voting for Danielle N. Most of the R's that remain in CO are RINO, not all, but many are.
 
If you have a dist, reduce base timing, @ 2*, open the spark plug gaps 10 to 15 thousandths.
Knock any carbon of the pistons.
Get the cat hot and keep it hot before the test, don't let it cool off
 
Wes Harden said:
If you have a dist, reduce base timing, @ 2*, open the spark plug gaps 10 to 15 thousandths.
Knock any carbon of the pistons.
Get the cat hot and keep it hot before the test, don't let it cool off
Click to expand...
Thanks for the input. This doesn't have a dist. Everything goes through an ECM. I cleaned off the pistons when I had the head off. The cat was hot pre-emission test. The cat is just toast. Probably the original cat. Was my in-laws car before the MiL died, daughter bought the car when my FiL moved from Garden City, KS to Wichita. Wasn't really driven much prior to my daughter purchasing it and had been neglected from care. The engine/trans is really in good shape. After the work I did 12/2021, compression on all 4 is now ~190psi. Should last a while, until my daughter runs into something. That's what's gonna kill that car now...operator error.
 
190psi is kinda on the high side. Nox is direct result of heat and compression. High Nox killed the Hemi and the air cooled vw.
 
Wes Harden said:
190psi is kinda on the high side. Nox is direct result of heat and compression. High Nox killed the Hemi and the air cooled vw.
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Yeah, agree. 190 seemed high to me too. A guy that rebuilds the LD9s told me that it's within nominal range though. Suppose to be a pretty good engine, it's just a freakin' PITA to work on. I told my daughter, the next time it needs work...find someone else. That didn't last long, ha.

I also asked one shop if that could be the reason for the high NOx (higher compression = higher combustion temps), he said not really. It's never knocked. I actually thought about just filling up with higher octane fuel to see if it would test, but didn't.
 
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Maybe Co just limited you right into an electric car. Seems unreasonable to me to tighten the standards on older cars with older tech. Should remain the same as when the car was mfg
 
Wes Harden said:
Maybe Co just limited you right into an electric car. Seems unreasonable to me to tighten the standards on older cars with older tech. Should remain the same as when the car was mfg
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that's what it used to be. If I have to go electric...I'll set something up like a locomotive. Burn diesel to power an electric motor, ha.
 
I just had my husband in laws, wife's ex, tundra in due to some kook slicing off the cats at the park and ride in Boulder. Ended up getting 48 state cats through rock auto. Had to send em to my mom in Michigan and have her send em to me. Pita but cut the cost by $650. Looks like Cheyenne Wyoming has exhaust shops popping up by the dozen now. Co has no way to tell if it's a Cali rado cat or not. Zero inspection other than peek under. Crazy crap to deal with for another layer of fun.
 
California cats have it stamped in the the body. I also believe they are serial numbered
 
If your car has an EGR system I'd start there. Plugged ports or a bad EGR valve can make the NOX to go high. Some of the cars had a ported EGR inside the manifold usually directly underneath the throttle body. I worked at Cadillac in the late 70's and the way they had the NOX set up the ports under the throttle body were always getting carboned up, some to a point where the intake manifold had to be removed to clean the passages! Also, check your catalytic. Some car engines took a 3 way catalytic (BIG$$$) and substituting a 2 way cat will NOT work! I hope this helps your diagnostic venture.
 
4X4ForDad said:
If your car has an EGR system I'd start there. Plugged ports or a bad EGR valve can make the NOX to go high. Some of the cars had a ported EGR inside the manifold usually directly underneath the throttle body. I worked at Cadillac in the late 70's and the way they had the NOX set up the ports under the throttle body were always getting carboned up, some to a point where the intake manifold had to be removed to clean the passages! Also, check your catalytic. Some car engines took a 3 way catalytic (BIG$$$) and substituting a 2 way cat will NOT work! I hope this helps your diagnostic venture.
Click to expand...
In December when I was working on it(heads, timing chain etc), The EGR appeared good and fairly clean. It's electronically controlled and was told that if it's bad, it would throw a EGR code, which it hasn't. After running a temperature test that show the output temp cooler than the input, no doubt that the cat is bad.

I thought about having the EPA Wagner cat sent to my BiL in Wichita or nephew in Lawrence, then have them send it here...but didn't go that route.
 
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Short story...Buick Skylark exhaust replacement is complete. Probably one of the easier exhausts I've done, with the exception of my '67 Chevelle SS, glass packs direct to headers. No major obstacles, although for a bit, it looked like getting the resonator pipe section over the rear axle was going to be an issue due to axle-chassis clearance and lack of space under the car, I was able to get it over.

BAFX sent me another Bluetooth adapter, so must have been an issue with the adapter it self.

I replaced up/down stream O2 sensors as well. The upstream varies, and the downstream is fairly constant but does vary depending on accelerator position. I'm thinking the MAP sensor might be going out because I'm noticing that the engine RPMs are in sync with the variation of the upstream O2 sensor. Next weekend I'll get it smog'd again and compare the pre/post test numbers.
 
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