CA Emission Techs Enter Here

[paulo57509]

The '92 Lumina failed emissions tests today. Typically, it failed with high NOx readings. The test numbers are below.

Since the HC numbers are low, I'm going to assume for now that the cat is working (it doesn't necessarily mean the NOx section is working).

Since the measured O2 levels are also low, I'm also going to assume the mixture is not lean.

The vehicle does have an exhaust leak down stream of the O2 sensor and up stream of the cat at the exhaust manifold flange.

I don't think the exhaust leak is contributing to erroneous NOx readings (it might be contributing to the low HC readings comparing 2007 to 2011). Comparing 2011 test numbers to 2007 (I couldn't locate the test results for 2009) it doesn't seem that the NOx numbers differ that much from 4 years ago (25MPH test speed not withstanding). I know when and where the exhaust leak manifested itself. It wasn't there in 2007.

After I get the exhaust leak repaired (new head pipe), I'm going to focus checks on the EGR system.

Question: Should I repair the exhaust leak and re-test immediately or repair the exhaust leak and chase any EGR gremlins and then re-test?

Thanks for your comments and advice.

Curious Observation: Look at the maximum allowable numbers for HC, CO and NOx between 2007 and 2011. Notice anything strange? Yes conspiracy theorists; this is how the state of CA gets older vehicles off the road.

 

[beast3300]

If there is an exhaust leak before the cat, the cat will suck air in and increase NOx. I would fix all exhaust leaks and run a bottle of Isoheet red. Just before going to echeck or whatever CA calls it, run the [censored] out of it on the expressway. 80mph for 30 mins to get the cat super hot then go test it.

 

[HTSS_TR]

High NOx article: http://www.smogtips.com/failed-high-NO-nitrous-oxide.cfm

 

[Trav]

Exhaust leak pre cat will give the engines ECM false lean readings and the leak after the cat will also give a false reading to the testing gas analyzer as can be seen in the results.
Non of the readings are accurate or valid. You need to repair all the exhaust leaks to get any sort of accurate numbers.

This engine could and probably does have much higher readings than are being shown but cant be determined accurately because of false air in the system.
With false exhaust ECM input the readings will be all over the place, its more than possible there are no EGR gremlin.

 

[oldmaninsc]

In California at least, the machine will detect if there is too much oxygen, and abort the test. Ask me how I know! It doesn't take much of an exhaust leak either.

 

[Trav]

This is true of almost all TSI and dyno testing units but this case is a little different in that it has a pre and post exhaust leak.

A post cat leak only will void testing almost immediately.
A pre cat leak will cause high readings and a fail but together one nullifies the other to some degree and can sometimes "fool" the analyzer from automatically rejecting the vehicle.

 

[paulo57509]

Originally Posted By: Trav
Exhaust leak pre cat will give the engines ECM false lean readings and the leak after the cat will also give a false reading to the testing gas analyzer as can be seen in the results.
Non of the readings are accurate or valid. You need to repair all the exhaust leaks to get any sort of accurate numbers.

This engine could and probably does have much higher readings than are being shown but cant be determined accurately because of false air in the system.
With false exhaust ECM input the readings will be all over the place, its more than possible there are no EGR gremlin.


My original post wasn't clear. There is only one exhaust leak and it's before the cat. The leak is also down stream of the O2 sensor. I would think that if this is making the ECM think lean, the NOx would be lower (at the expense of higher HC readings) because the ECM would demand a richer mixture.

Of course, I understand with an exhaust leak that this is like trying to diagnose electrical issues with a dead battery; one cannot believe any test results.

I'll repair the exhaust leak, te-test and report back.

Thanks all.

 

[Trav]

Sorry i misunderstood your post, it was clear my English comprehension skills sometimes fail me, but no problem.
If the leak is after the O2 sensor but before the cat the induction of additional fresh air into the cat should not affect the ECM so no it wouldn't go rich trying to correct a lean condition.
The fresh air would certainly raise the cat temperature and increase NOx readings.

This is exactly the same function of a secondary air pump, to raise cat temps on a cold cat, but the pump (electric) stops or get diverted after about 10-30 seconds after cold start.
I think once you fix the leak NOx will drop significantly and the other values will increase slightly.

 

[paulo57509]

Originally Posted By: Trav
Sorry i misunderstood your post, it was clear my English comprehension skills sometimes fail me, but no problem.
If the leak is after the O2 sensor but before the cat the induction of additional fresh air into the cat should not affect the ECM so no it wouldn't go rich trying to correct a lean condition.
The fresh air would certainly raise the cat temperature and increase NOx readings.

This is exactly the same function of a secondary air pump, to raise cat temps on a cold cat, but the pump (electric) stops or get diverted after about 10-30 seconds after cold start.
I think once you fix the leak NOx will drop significantly and the other values will increase slightly.


Trav, no problem with your comprehension. What you're reading has to be written clearly in the first place.

The leak acting as secondary air crossed my mind a few minutes after I posted last night.

Thanks again for you help.

 

[Bladecutter]

I'm amazed that no one has recommended that you inspect your EGR circuit, as those are famous for having clogged up on those cars.

Remove the EGR valve, and look at the pipe it connects to to see if its clogged. If yes, clean out all the way through, and also check the pipe that then connects to the throttle body.

Lack of EGR functionality also is a source of High NOx readings.

BC.

 

[paulo57509]

Originally Posted By: Bladecutter
I'm amazed that no one has recommended that you inspect your EGR circuit, as those are famous for having clogged up on those cars.

Remove the EGR valve, and look at the pipe it connects to to see if its clogged. If yes, clean out all the way through, and also check the pipe that then connects to the throttle body.

Lack of EGR functionality also is a source of High NOx readings.

BC.


Originally Posted By: paulo57509
After I get the exhaust leak repaired (new head pipe), I'm going to focus checks on the EGR system.

 

[Merkava_4]

Originally Posted By: Trav

This is exactly the same function of a secondary air pump, to raise cat temps on a cold cat, but the pump (electric) stops or get diverted after about 10-30 seconds after cold start.


I got a secondary air injection pump on my Buick - I had always
wondered what it's for - now I know. Thank you sir.

 

[paulo57509]

Here's the cause of the exhaust leak.

The sheet metal inner ring fits into the exhaust manifold bore; the head pipe "bell" mates to the larger donut OD. The design allows the engine to be tilted forward for access to the rear cylinder head.

When I bottomed out the undercarriage earlier this year, it must have dragged the exhaust system towards the back of the car. The head pipe flange being spring loaded, pulled back, donut became unseated and the head pipe pulled back into the manifold re-capturing it.

Replacement of the donut was pretty straight forward. I replaced the head pipe too. It was tweaked as well. No PB Blaster or penetrating oil was necessary for the bolts. They did get anti-seize upon re-installation.

I'll bring it back for a re-test tomorrow (if the shop is open) and will post the results.

 

[Rand]

my grandma's 93 lumina that I e-check every year here in ohio always BARELY passes.. one year she had a rust hole and IT was total wack results. Got that fixed..
Ran it 20min on highway.. it passed again (by a very small amount)

Apparantly 2011 was that last time.. she just quit driving at 85

 

[paulo57509]

The test station was closed for the New Year weekend so I had some time on my hands.

I dug out the emissions test results going back to 2005 and plotted the NOx numbers. The measured results from the 2011 test (failed) would have passed (barely - even with the exhaust leak) IF the car were still being tested against 2009 limits. Sometime after 2009, CA decided to lower the passing limits thus the issue I'm currently having now.

Something other than an exhaust leak is going on here. I suspect it isn't just one thing that's the issue.

Curious notes with no conclusions drawn....yet:

1. The 15mph and 25mph numbers diverge dramatically. I know that 15mph can typically be a tough test to pass.

2. The Cat appears to have been deteriorating (at least for NOx at 15mph) over the years. Interesting to note that there was a bad coil back in Jul-2009 that could have done it in.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1546529&fpart=1

3. Dramatic drop in 25mph measured values between 2005 and 2007. I did run injector/combustion chamber cleaner through the fuel rail in May-2007. Can removal of combustion chamber deposits (hot spots) make that dramatic a difference?

4. This is just a snap shot of one category that is tested. I think HC, O2, etc. needs to be considered for a complete picture.

 

[paulo57509]

Just posting to close the loop.

I'm just got around to closing to book on this one. Bottom line, it was a bad cat.

I purchased a direct fit Magnaflow last month off an ebay which really wasn't. There was a pipe size mismatch on both ends. The local muffler shop installed it for $70 (Man, I wish I had the room and $$$$ for one of those pipe bender/expander/reducer machines).

I immediately drove it across the parking lot to the inspection place and their machine spit this out:

Compare it with the "fail" numbers:

For those of you that live in CA, I have heard/read about some controversy regarding the inspection tech confirming that the replacement cat has CARB certification numbers; this is true in my case. I overheard the tech on the phone with the State forwarding make, model, year and CARB numbers (stamped on the cat) over the phone.