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New Engine won't pass emissions, High NOX

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New Engine won't pass emissions, High NOX

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Old 11-05-2018, 03:57 PM
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New Engine won't pass emissions, High NOX

This is a continuation from my previous rebuild thread here: https://www.camaroz28.com/forums/lt1...t-look-886753/

With the new engine in, I failed smog due to high NOX.
NOX around 1000 for both speeds




Injuneer replied:
The first and second logs were just at idle. The first log showed very good results on the A/F ratio - LTFT's 130 left/128 right. But as I mentioned, it wasn't the same in the second log. As it turned out, the right bank was fairly stable at idle, with the LTFT ranging from 125 to 130.(-2.3% to +1.6%) But the left bank was starting to show instability, with it trending toward the lean side. The LTFT ranged from 128-138.(0% to +7.8%). The results were a little muddled by several instance of revving the engine, which is really pointless, since it doesn't show much of anything with the engine not under load.

Then we got sidetracked on the starter, and I didn't do much more with the second idle data log. The third log was for analysis of the starter problem.

What you need now is a log of the engine operating under load, out on the road. There are 15 more critical LTFT cells, and none of them are used until the engine it under variable load/variable RPM. Running lean helps create NOx in two ways - excess O2 is available to combine with the nitrogen, and lean mixtures burn hotter, providing the heat for the oxygen+nitrogen reaction. But, running lean will usually result in very low HC and CO, and your HC isn't that low.

As I noted before, I really think you need to start a new thread. Leave this one as a record of the rebuild. The new one will cover the operating issues with the engine. As mentioned immediately above, there's just a lot of posts for anyone to go back and review.
Ok thanks, I will take a new datalog of me driving normally out on the street to get a better idea of what's going on.

I'm also going to have to stop by a muffler shop to see what the rattling is if I can't figure it out myself. There is rattling from the catalytic converter area, and there is a rattling inside of the muffler itself. So there is a chance that the material inside of the cat is breaking up and making its way down the exhaust.

I will have to start with EGR diagnosis and troubleshooting first to check the vacuum and stuff first.

I'll post back once I have a new datalog

Last edited by ridiqls; 11-10-2018 at 11:19 PM.
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Old 11-05-2018, 04:08 PM
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Re: New Engine won't pass emissions, High NOX

Question, can someone confirm if the 1994 Camaro Lt1, 6 speed CA model has a vent line from the catalytic converter to somewhere else? I looked up catalytic converters in Autozone that fit my car and it is showing a universal cat with no vent/air line.

But I am reading conflicting things.. My cat does not have this vent line btw, and it is a replacement cat by the previous owner. Trying to eliminate this as an issue.
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Old 11-05-2018, 04:17 PM
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Re: New Engine won't pass emissions, High NOX

IDK about what type of CAT you need. shbox.com likely has the info you need on that

exhaust leak or plugged CAT can certainly cause smog test fail

NOX can be due to high combustion chamber temps from a lean condition and also a faulty EGR system

A scan would show what your STFT are and if lean can be a contributing factor
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Old 11-05-2018, 05:59 PM
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Re: New Engine won't pass emissions, High NOX

I've never seen a cat vent line on any LT1 f-body.
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Old 11-05-2018, 06:07 PM
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Re: New Engine won't pass emissions, High NOX

Originally Posted by ridiqls View Post
This is a continuation from my previous rebuild thread here: https://www.camaroz28.com/forums/lt1...t-look-886753/

With the new engine in, I failed smog due to high NOX.





Injuneer replied:



I'm also going to have to stop by a muffler shop to see what the rattling is if I can't figure it out myself. There is rattling from the catalytic converter area, and there is a rattling inside of the muffler itself. So there is a chance that the material inside of the cat is breaking up and making its way down the exhaust.

I will have to start with EGR diagnosis and troubleshooting first to check the vacuum and stuff first.

I'll post back once I have a new datalog
OP

read last few posts of your other thread and it says you have replaced the EGR...so that should be good. The EGR electrical solenoid (not sure if its called that) that is on the DS intake manifold with vac lines going to it "may" be faulty. Not sure if there is a way to test that. If you push in on the EGR diaphragm with engine idling, it should stall if you hold it in. It is working if it does that.

Your "noise" from CAT area needs to be checked as a clogged CAT will cause emission fails and also pre 02 exhaust leaks. A muffler shop can use a back pressure gauge to see what it is pre & post CAT. If pressure is significantly lower on the output side of CAT that means it is clogged. You can also use a IR temp gun to see what temps are front & back. IIRC if temps are quite a bit hotter on front of CAT than back than that is a indication of a clogged CAT. Of course the "glowing red" CAT is a very clear indication of a clogged CAT

Are the 02 readings good and fairly = on both banks?

Running a data log as Fred suggests will provide real engine operation data which you are fortunate to have Frd review and comment on.
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Old 11-05-2018, 06:41 PM
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Re: New Engine won't pass emissions, High NOX

Originally Posted by shoebox View Post
I've never seen a cat vent line on any LT1 f-body.
Strange, I thought I read that there were vent lines. Ok good to know I dont have the wrong cat.


Originally Posted by Chimera96 View Post
OP

read last few posts of your other thread and it says you have replaced the EGR...so that should be good. The EGR electrical solenoid (not sure if its called that) that is on the DS intake manifold with vac lines going to it "may" be faulty. Not sure if there is a way to test that. If you push in on the EGR diaphragm with engine idling, it should stall if you hold it in. It is working if it does that.

Your "noise" from CAT area needs to be checked as a clogged CAT will cause emission fails and also pre 02 exhaust leaks. A muffler shop can use a back pressure gauge to see what it is pre & post CAT. If pressure is significantly lower on the output side of CAT that means it is clogged. You can also use a IR temp gun to see what temps are front & back. IIRC if temps are quite a bit hotter on front of CAT than back than that is a indication of a clogged CAT. Of course the "glowing red" CAT is a very clear indication of a clogged CAT

Are the 02 readings good and fairly = on both banks?

Running a data log as Fred suggests will provide real engine operation data which you are fortunate to have Frd review and comment on.
Ok so I tested the EGR valve itself one more time, it's holding vacuum. If I vacuum the valve while the car is running, it won't HOLD vacuum but it will stutter the engine. I imagine if I just press the diaphragm in it will kill the engine. I haven't tested the solenoid yet. I think Scan9495 has an option under the Actuators page to turn EGR on to 50% and 100%. So maybe that will activate the vacuum on the solenoid, but kind of confused about that part.


Regarding the rattling noise under the passenger side.. so the damn flange connecting the y-pipe (with cat) to the catback exhaust was loose and rattling around. I don't know if it was enough to cause a major exhaust leak at this connection but I didn't hear an exhaust leak and I'm not sure if a post-cat exhaust leak would affect emissions? Not clear on that. Anyway, it's tightened back down.

I'm going to pick up an IR temp gun as it seems like the best bang for buck for figuring out if the cat can be ruled out or not. So once I test that and if the post cat side of the exhaust is hotter by 100-150 deg, then we can rule out the cat as the problem.

I used this tool to tune out VATS Free Online Tuning Service ? fbodytech
and it has an option for cooling fans to come on sooner. That should keep the temps down a bit in the engine. I don't know at what temp it's set at but if it's anywhere around 200 deg for the first fan, then that'd be ideal.

Once I flash the new bin, I'll datalog to see if there are any issues with the engine's AFR. Appreciate Fred's help on this
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Old 11-05-2018, 06:53 PM
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Re: New Engine won't pass emissions, High NOX

exhaust leak post CAT should not affect emission testing

IR temp guns are fairly cheap now. IIRC Harbor Freight has them for $20. They come in handy for all kinds of checks on the motor. I use mine to check exhaust header temps to see if one cyl is running hot or colder than others

Its "combustion" temp...not "engine coolant" temp that effects NOX. You would want the motor running at more stock operating temps for smog tests. The CATS light off better

Your motor is new so there should not be a bunch of carbon build up on pistons which can increase "combustion" temps

A lean condition can cause higher combustion temps...but monitoring your STFT and LTFT should show if fueling is the cause of a lean condition

You get a good data og under load as Fred recommends and post it for his comments. Ideally that data log will reveal a "why" to the NOX issue
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Old 11-05-2018, 09:12 PM
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Re: New Engine won't pass emissions, High NOX

The connection on the dual-bed (or 3-way) cats is not a “vent”.... it’s the connection required for air injection from the AIR (secondary air pump). They stopped using that system on the 3rd Gens. The AIR system had a diverter valve. On startup the pump forced air into the exhaust manifolds to burn excess fuel and heat up the cat. Then a diverter valve directed the AIR pump flow into the connection on the cat, where the air was used in the downstream catalyst bed to oxidize unburned HC and convert CO to CO2.

4th Gen use a 3-way converter without any secondary air injection.
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Old 11-05-2018, 09:15 PM
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Re: New Engine won't pass emissions, High NOX

Originally Posted by Injuneer View Post
The connection on the dual-bed (or 3-way) cats is not a “vent”.... it’s the connection required for air injection from the AIR (secondary air pump). They stopped using that system on the 3rd Gens. The AIR system had a diverter valve. On startup the pump forced air into the exhaust manifolds to burn excess fuel and heat up the cat. Then a diverter valve directed the AIR pump flow into the connection on the cat, where the air was used in the downstream catalyst bed to oxidize unburned HC and convert CO to CO2.

4th Gen use a 3-way converter without any secondary air injection.
Thank you for clarifying. You posted at the same time I was about to so there is a second reply coming.
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Old 11-05-2018, 09:16 PM
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Re: New Engine won't pass emissions, High NOX

BAD CAT (something else is wrong)

Pre-cat Temp reading:


Post-Cat Temp reading:



The temp should be way higher post cat, but instead it is higher pre-cat. I'm guessing the cat is messed up and potentially clogged.

The previous owner replaced the Catalytic Converter on Mar 2013 at 117,000 miles. So about 5.5 years ago and 18k miles ago. I think the cat is dying prematurely or the cat is a garbage quality aftermarket.



1) I have to replace the cat. Great.



2) Now that that's out of the way, I took a datalog of a full 15 min drive to Harbor Freight.

I don't know how to read this stuff well but I noticed something that might be off:
"B1 LT Fuel Trim/BLM" is reading higher about 10 than the rest (B1 LT, B1 ST, B2 ST. These are reading around 128) B1 LT is reading around 138.

This is exactly what Fred had mentioned to me before.

Fred, what does this mean and what did you mean by there are 15 other fuel cells? I'm guessing LT is the left side, B1.. is bank 1? not sure... I do not yet understand this deeply when it comes to this stuff and the implications for mechanical repair. Running lean means, possibly a fuel injector that is clogged or weak?


3) I was mistaken about the EGR duty cycle not changing. It does change during the drive.



Injuneer, if you have the time and still want to help, I attached the datalog file. Thank you.

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Old 11-05-2018, 09:29 PM
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Re: New Engine won't pass emissions, High NOX

To test for actual exhaust gas flow into the engine, with the engine idling, open the EGR valve. The engine should stumble to the point (or close to) of stalling. You could use a vacuum pump connected to the hose that goes directly to the EGR valve, bypassing the EGR vacuum solenoid.

To insure the EGR vacuum solenoid is effectively shutting of vacuum to the EGR valve, use the vacuum pump to pull a vacuum on the hose going to the solenoid. To insure the EGR solenoid is working, with the vacuum pump still on the hose to the solenoid, unplug the harness. Apply 12 volts to the A pin of the solenoid, and a ground to the B-pin, Solenoid should open and open the EGR valve.

There is a code in OBD-1 for no/low EGR flow (DTC 32). On the road, engine under load, PCM cycles the EGR valve and looks for the expected change in MAP. Unfortunately (or perhaps fortunately if you are deleting EGR) the diagnostic is not very reliable, and in many cases you can delete the EGR system and not see DTC 32.
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Old 11-05-2018, 09:44 PM
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Re: New Engine won't pass emissions, High NOX

I just remembered you had a scan guide so I just went thru it.

So B1 LT Fuel Trim/BLM would be the driver's side and because it's high, it is the PCM compensating for a lean condition if it were not in a closed loop correct?

Is there a way to drill down into potentially what is causing a lean condition on the driver's side? It's gotta be the fuel injectors right?

Does the datalog show which cylinders it might be?


I was wrong in my post above, the EGR duty cycle does change throughout the drive. But I will double check the solenoid function.

Can I just click this "EGR 100% button" on the Scan9495 software under Actuators while the car is running and check with my fingers to see if it creates a vacuum on the hose going from the solenoid to the EGR valve?
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Old 11-05-2018, 09:56 PM
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Re: New Engine won't pass emissions, High NOX

B1 LT = Bank 1 (Driver sIde), Long Term Fuel Trim
B2 LT = Bank 2 (Passenger sIde), Long Term Fuel Trim

The ones above are the most important when looking at the data. These are the “memory” or “learned” part of A/F ratio control.

ST = Short Term Fuel Trim, left and right

The short terms are instantaneous responses to the O2 sensor feedback. The PCM toggles them back and forth, slightly above 128 (slightly rich), and slightly below 128 (slightly lean). That helps the cat work. As long as the O2 sensors are showing these slightly rich/lean readings, the LTFT's don't change. The O2 sensors would be averaging about 0.450 volts over a period of time. But (for example) if the injector isn't supplying enough fuel (running lean), the average O2 reading will drop below 0.450 volts, so the PCM will raise the “learned” LTFT above 128, until the average O2 sensor reading returns to 0.450 volts, and store the new number in the corresponding LTFT “Cell”

In the data log, in the column just to the left of the two O2 sensor voltage readings, is the “Cell” #. Cells are defined by a grid of MAP (representing engine load) on one axis and RPM on the other axis. Cell 0 (seldom seen) is very low engine load and very low RPM. Cell 15 is high engine load/high RPM. Cells 1 through 14 fit in between 0 and 15, and are various combinations of RPM and MAP.

There’s also:

Cell 16. - idle
Cell 17 - decel
Cell 18 - accel, generally in open loop (but sometimes in closed loop, but it gets complicated)

Cells 17 and 18 are mathematically calculated from the other cells.

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Old 11-05-2018, 10:16 PM
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Re: New Engine won't pass emissions, High NOX

Originally Posted by ridiqls View Post
I just remembered you had a scan guide so I just went thru it.

So B1 LT Fuel Trim/BLM would be the driver's side and because it's high, it is the PCM compensating for a lean condition if it were not in a closed loop correct?
It’s compensating for a lean condition in closed loop. Learning is not enabled in open loop. In open loop, it uses the LTFT's it learned in closed loop (Cells 16, 17, 18).

Is there a way to drill down into potentially what is causing a lean condition on the driver's side? It's gotta be the fuel injectors right?
Not that simple. The lean condition can be any number of things that only affect one bank of the engine, and can be a “true” lean, or a “false” lean.

True lean:
- injector(s)
- vacuum leak
- leaky valve guide(s)

False lean:
- faulty O2 sensor
- exhaust leak before O2 sensor
- misfire(s)

Does the datalog show which cylinders it might be?
No
I was wrong in my post above, the EGR duty cycle does change throughout the drive. But I will double check the solenoid function.
The EGR duty cycle is just what the PCM is commanding. There is no feedback on whether this is actually happening, except DTC 32 mentioned above.

Can I just click this "EGR 100% button" on the Scan9495 software under Actuators while the car is running and check with my fingers to see if it creates a vacuum on the hose going from the solenoid to the EGR valve?
Yes. You could also see if it opens the EGR valve and causes the engine to run rough/stall. I never actually use Scan9495 since I don’t use the factory PCM to run my engine. You are one step ahead of me on this.
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Old 11-05-2018, 10:26 PM
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Re: New Engine won't pass emissions, High NOX

When you measured the temperature across the cat, was the engine fully warmed up, and had the car been driven enough for the internals of the cat to reach ~600°F? Cat doesn't work until it gets that hot.

Previous owner could have damaged the cat if:
- he drove the car for a long period with misfires
- had a head gasket leak that caused silicates from the anti-freeze to deposit on the O2 sensors and then the cat (ding, ding)
- used leaded fuel at the race track
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