Emissions Trouble - High NO only at higher speed
06-11-2018, 08:16 PM
#1
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Emissions Trouble - High NO only at higher speed New to this forum.
I have a unique conversion: I installed a 2004 LM4 5.3l in my 2001 Jeep Wrangler. Fully aware that I live in an emissions testing county in VA I spent the money to put all 4 O2 sensors back in, added cat to new Magnaflo exhaust and have new purge and evap solenoids. The ECM has the stock programming in it for the engine I have.
Because of the conversion they used a: ASM2 Tailpipe Emissions Inspection.
It passed every test except the 25 mph NO ppm test. I did see another thread in here about failing this test but his was failing both high and low speed tests where mine is only the high speed test.
Any help here would be huge. I am highly mechanical, fairly good with electrical/electronics but very novice at the ECM/codes/monitors/programming/etc.
The actual values of the tests:
15 MPH TEST:
RPM: 1,591, VALID
HC: 27 ppm, limit 74, PASS
CO: 0.01%, limit 0.41%, PASS
NO: 1 ppm, limit 586, PASS
Dilution: 14.21%, VALID
25 MPH TEST:
RPM: 1,684, VALID
HC: 36 ppm, limit 72, PASS
CO: 0.01%, limit 0.40%, PASS
NO: 1,411 ppm, limit 531, FAIL
Dilution: 14.31%, PASS
Visible Smoke Inspection: PASS
I can send an image of the actual test report if that would be of any use.
At this point I do not have any idea on how to remedy this situation. Any help would be greatly appreciated
06-12-2018, 06:30 AM
#2
Here's a bump -- absolute mystery to me. Hell, there's barely 100 rpm difference in the two tests -- makes no sense at all that NOx would jump from nearly zero up to 3 times the limit. I gotta think that either the 1ppm reading or the 1411ppm reading is faulty. Can you simply have it retested perhaps at a different location (different equipment/operators)?
06-21-2018, 05:43 PM
#4
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what cat did you add? did you make sure the engine was fully up to temp and exhaust was nice and toasty before having them run it? how are your fuel trims looking when on that 25mph test?
06-22-2018, 08:53 AM
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It is a Magnaflo 3” cat; I will get the actual part number tonight and add it on here.
The engine was fully warmed up when I drove it to the shop but it did sit awhile waiting for the test.
They did not let me in the shop for the test.
I am unfamiliar with what you mean by “fuel trims”. What does this refer to and how would I get you the data?
I am taking it back in tomorrow for a retest and will try to get in there for the actual test.
The engine was fully warmed up when I drove it to the shop but it did sit awhile waiting for the test.
They did not let me in the shop for the test.
I am unfamiliar with what you mean by “fuel trims”. What does this refer to and how would I get you the data?
I am taking it back in tomorrow for a retest and will try to get in there for the actual test.
06-22-2018, 08:55 PM
#6
FWIW - My experience with sniffer type emissions may relate to the IM240 roller emissions test.
My 91 RS had to face the sniffer test for many years including HC ppm & NO ppm. With 300,000+ miles on the engine, the HC ppm & NO would test the same as a new car 12 ppm or less. With that said sometimes my car would fail and a retest was required.
Fresh oil always reduced the HC ppm. Replacing PCV valve and getting the PCV sorted with a good hoses and no vacuum leaks helped to.
Working EGR and / or a decarbon treatment helped reduce the NO. The NO emissions got up as the combustion temperature rises. I think as 2500 degrees combustion temp is reached NO skyrockets. I would get the engine a good decarbon treatment. ACDelco GM Top End/Upper Fuel Injection Cleaner X66p is outstanding. I've read it's often used when basically other top end cleaners fail at decarbon. I would try this for the decarbon treatment. When carbon build up in the cylinder head chamber it raises compression. This causes higher temperatures and more NO.
Keeping the cooling system in good condition can help.
Making sure no vacuum leaks are occurring.
Lean conditions will cause higher temperature and increase No levels. Confirm fuel pressure is good at ~58 psi. Make sure the MAF is in good condition with no broke wires etc. It might need cleaning.
I think some catalytic converters are designed specifically to work with the EGR system to scrub NO. Other catalytic converters are designed to scrub they NO without EGR assist. I suggest confirming the cat that was provided is the correct one for the application. Cam overlap can also play a role in the amount of NO.
The Top Tier approved gasoline brands have more detergents to keep the fuel system in good condition and fuel Injectors cleaner. While many will scoff at name brand gas it is better if Top Tier approved. My pet favorites Shell, Sunoco, Mobile, Exxon and so for more details.
https://www.toptiergas.com
My 91 RS had to face the sniffer test for many years including HC ppm & NO ppm. With 300,000+ miles on the engine, the HC ppm & NO would test the same as a new car 12 ppm or less. With that said sometimes my car would fail and a retest was required.
Fresh oil always reduced the HC ppm. Replacing PCV valve and getting the PCV sorted with a good hoses and no vacuum leaks helped to.
Working EGR and / or a decarbon treatment helped reduce the NO. The NO emissions got up as the combustion temperature rises. I think as 2500 degrees combustion temp is reached NO skyrockets. I would get the engine a good decarbon treatment. ACDelco GM Top End/Upper Fuel Injection Cleaner X66p is outstanding. I've read it's often used when basically other top end cleaners fail at decarbon. I would try this for the decarbon treatment. When carbon build up in the cylinder head chamber it raises compression. This causes higher temperatures and more NO.
Keeping the cooling system in good condition can help.
Making sure no vacuum leaks are occurring.
Lean conditions will cause higher temperature and increase No levels. Confirm fuel pressure is good at ~58 psi. Make sure the MAF is in good condition with no broke wires etc. It might need cleaning.
I think some catalytic converters are designed specifically to work with the EGR system to scrub NO. Other catalytic converters are designed to scrub they NO without EGR assist. I suggest confirming the cat that was provided is the correct one for the application. Cam overlap can also play a role in the amount of NO.
The Top Tier approved gasoline brands have more detergents to keep the fuel system in good condition and fuel Injectors cleaner. While many will scoff at name brand gas it is better if Top Tier approved. My pet favorites Shell, Sunoco, Mobile, Exxon and so for more details.
https://www.toptiergas.com
Last edited by 99 Black Bird T/A; 06-22-2018 at 09:15 PM.
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06-23-2018, 07:49 AM
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It is a Magnaflo 3” cat; I will get the actual part number tonight and add it on here.
The engine was fully warmed up when I drove it to the shop but it did sit awhile waiting for the test.
They did not let me in the shop for the test.
I am unfamiliar with what you mean by “fuel trims”. What does this refer to and how would I get you the data?
I am taking it back in tomorrow for a retest and will try to get in there for the actual test.
The engine was fully warmed up when I drove it to the shop but it did sit awhile waiting for the test.
They did not let me in the shop for the test.
I am unfamiliar with what you mean by “fuel trims”. What does this refer to and how would I get you the data?
I am taking it back in tomorrow for a retest and will try to get in there for the actual test.
Fuel trims are how much the ECU's is correcting the fuel injected amount based on the oxygen sensor. So if you fuel trims are high (>15%) then the ECU when referencing the maf/map is not supplying enough fuel, so without oxygen sensor feedback you would be 15% lean creating high NOx. The oxygen sensors will correct for this though, telling the ECU to add fuel but only after the oxygen sensor sees the lean air/fuel mixture. What generally ends up happening is although the o2 sensors correct the lean condition, every small tip-in or speed/load transition will cause a short lean event, when you compile all of these events it results in the catalyst not able to convert properly.
TLDR: hook up a scan tool or HP tuners and try to replicate the drive cycle you're failing, you'll likely see lean fuel trims (positive numbers). Start diagnosing the cause of those lean trims, and that should fix your issue.
06-23-2018, 08:01 AM
#9
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Well today was retest day and it failed again. Similar results: HC and CO passed but NO failed although this time NO failed both the 15 mph and 25 mph tests. Full results are:
The actual values of the tests:
15 MPH TEST:
RPM: 1,660 VALID
HC: 14 ppm, limit 74, PASS
CO: 0.01%, limit 0.41%, PASS
NO: 1,372 ppm, limit 586, PASS
Dilution: 14.91%, VALID
25 MPH TEST:
RPM: 1,667, VALID
HC: 18 ppm, limit 72, PASS
CO: 0.01%, limit 0.40%, PASS
NO: 1,679 ppm, limit 531, FAIL
Dilution: 14.91%, PASS
Visible Smoke Inspection: PASS
So this time I got a chance to talk to the tech. I had run the motor a good 30 min before the test and made sure I was the first one in line so everything was good and heated up. He said this is not necessary as the analyzer will not even take the test until the cat is heated up to a certain temp. Regardless that variable should be eliminated.
He said he believes that the cat I bought must be a “2 way “ cat designed to take HC and CO out but not NO. He said that I probably need to get a “3 way” cat that is designed to take the NO out too. Any thoughts here? There was another post on here that the end solution was the guy put the OEM cat back on in place of aftermarket and passed his test..?
Lastly, some mentioned EGR but this engine does not have EGR on it so that cannot be the issue.
Greatly appreciated any help
The actual values of the tests:
15 MPH TEST:
RPM: 1,660 VALID
HC: 14 ppm, limit 74, PASS
CO: 0.01%, limit 0.41%, PASS
NO: 1,372 ppm, limit 586, PASS
Dilution: 14.91%, VALID
25 MPH TEST:
RPM: 1,667, VALID
HC: 18 ppm, limit 72, PASS
CO: 0.01%, limit 0.40%, PASS
NO: 1,679 ppm, limit 531, FAIL
Dilution: 14.91%, PASS
Visible Smoke Inspection: PASS
So this time I got a chance to talk to the tech. I had run the motor a good 30 min before the test and made sure I was the first one in line so everything was good and heated up. He said this is not necessary as the analyzer will not even take the test until the cat is heated up to a certain temp. Regardless that variable should be eliminated.
He said he believes that the cat I bought must be a “2 way “ cat designed to take HC and CO out but not NO. He said that I probably need to get a “3 way” cat that is designed to take the NO out too. Any thoughts here? There was another post on here that the end solution was the guy put the OEM cat back on in place of aftermarket and passed his test..?
Lastly, some mentioned EGR but this engine does not have EGR on it so that cannot be the issue.
Greatly appreciated any help
06-23-2018, 08:06 AM
#10
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Also, in response to 99 Black Bird: the motor I bought was bare and only has 7,000 miles on it. Because it was bare and not a pullout I ended up having to buy new sensors and I went with OEM GM for all of it: MAP sensor, evap, purge, all 4 O2 sensors. The MAF and throttle body were there but had to buy a used throttle control computer and throttle pedal. I am thinking that through my inexperience I probably bought a cat that, while it sounds great, does not do the job of a factory cat.
06-23-2018, 09:57 AM
#11
G-Money, that sounds like a sweet engine and set up 
Sounds likely it's the cat and definitely not carbon build up with those low miles.
Kook's has a series of high performance "green" cats that are EPA certified according to their website. At the PRI show in 2017 Kook's told these cars can support 900+ hp and the front and rear O2's will function normally. If you want a high flowing Kook's might be able to help. They should also know if their EPA certified cat will scrub the NO from the exhaust.
https://www.kooksheaders.com/green
Sounds likely it's the cat and definitely not carbon build up with those low miles.Kook's has a series of high performance "green" cats that are EPA certified according to their website. At the PRI show in 2017 Kook's told these cars can support 900+ hp and the front and rear O2's will function normally. If you want a high flowing Kook's might be able to help. They should also know if their EPA certified cat will scrub the NO from the exhaust.
https://www.kooksheaders.com/green
06-23-2018, 10:47 AM
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Thanks for the quick reply. I will check them out and either get one of those or a OEM cat. Probably a good excuse to get a welder and learn to weld thin stuff too. This whole thing is a bit annoying but that’s part of the deal. Jeep sure goes like hell with that motor even bone stock. Magnaflo turns a lot of heads too: what they hear and see just don’t match...
thanks
thanks
06-24-2018, 08:01 PM
#13
As I suspected --- your first test had a bad 15 mph NOx number -- clearly it wasn't "1". Also, interesting that even though your second test shows a 15mph NOx number WAY above 586 - it says "PASS". Nothing like clarity from the testing station to clarify things.
In the old days of 2 cats inline instead of just one, the front cat usually had connections for the air pump to add air (read = oxygen) to the cat. That extra O2 was necessary in order to "burn", or oxidize the excess HC's and to convert CO to CO2. 3-way cats (and contemporary ECU's) accomplish this by 1) controlling mixture (run lean = excess oxygen is present in the exhaust, unburned HC's minimized) and 2) stripping the excess oxygen molecules off the NOx (NO2, NO3, etc) early in the cat thereby converting it to N2 and freeing up the O2 for use on the back end of the cat to turn unburned fuel into H2O and CO2, and to turn CO into CO2. All of that to say, if the ECU you're using wasn't designed to work with a 3-way cat, you may not get the result you need.
In the old days of 2 cats inline instead of just one, the front cat usually had connections for the air pump to add air (read = oxygen) to the cat. That extra O2 was necessary in order to "burn", or oxidize the excess HC's and to convert CO to CO2. 3-way cats (and contemporary ECU's) accomplish this by 1) controlling mixture (run lean = excess oxygen is present in the exhaust, unburned HC's minimized) and 2) stripping the excess oxygen molecules off the NOx (NO2, NO3, etc) early in the cat thereby converting it to N2 and freeing up the O2 for use on the back end of the cat to turn unburned fuel into H2O and CO2, and to turn CO into CO2. All of that to say, if the ECU you're using wasn't designed to work with a 3-way cat, you may not get the result you need.
06-25-2018, 07:30 PM
#14
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Michael - that was my bad: I cut and pasted from the first thread and changed the values but forgot to change the PASS to FAIL on the second test. Should have been:
15 MPH TEST:
RPM: 1,660 VALID
HC: 14 ppm, limit 74, PASS
CO: 0.01%, limit 0.41%, PASS
NO: 1,372 ppm, limit 586, FAIL
Dilution: 14.91%, VALID
25 MPH TEST:
RPM: 1,667, VALID
HC: 18 ppm, limit 72, PASS
CO: 0.01%, limit 0.40%, PASS
NO: 1,679 ppm, limit 531, FAIL
Dilution: 14.91%, PASS
Visible Smoke Inspection: PASS
Also, it appears that all of the stock GM cats are 1 per bank, 2 total. There is really not enough room for that in my application. I only have 6 inches between the cat and muffler and there are 2 O2 sensors in that same spot! On the front end the Y pipe is welded directly to the cat. Is there a one cat GM solution or do I need to go to something like the Kooks green cat aftermarket? As you can tell from the previous posts I prefer to spend a little more on OEM and try to avoid future issues.
thanks for the help.
G
15 MPH TEST:
RPM: 1,660 VALID
HC: 14 ppm, limit 74, PASS
CO: 0.01%, limit 0.41%, PASS
NO: 1,372 ppm, limit 586, FAIL
Dilution: 14.91%, VALID
25 MPH TEST:
RPM: 1,667, VALID
HC: 18 ppm, limit 72, PASS
CO: 0.01%, limit 0.40%, PASS
NO: 1,679 ppm, limit 531, FAIL
Dilution: 14.91%, PASS
Visible Smoke Inspection: PASS
Also, it appears that all of the stock GM cats are 1 per bank, 2 total. There is really not enough room for that in my application. I only have 6 inches between the cat and muffler and there are 2 O2 sensors in that same spot! On the front end the Y pipe is welded directly to the cat. Is there a one cat GM solution or do I need to go to something like the Kooks green cat aftermarket? As you can tell from the previous posts I prefer to spend a little more on OEM and try to avoid future issues.
thanks for the help.
G
06-26-2018, 07:55 PM
#15
high oxides of nitrogen readings = either a lean condition or very high combustion pressures.
even a 3 way catalyst isnt gonna knock down NO levels from 1700 to 500ppm .
instead of shooting the parts cannon at it, try to get in touch with a tuner that can add some fuel
even a 3 way catalyst isnt gonna knock down NO levels from 1700 to 500ppm .
instead of shooting the parts cannon at it, try to get in touch with a tuner that can add some fuel
06-26-2018, 09:05 PM
#16
With a matching stock system (except for cats) can’t understand why fuel would need to be added. If it were that much out of spec lean, CEL/MIL/error codes would be present I’d think. If there are no error codes - that would seem to point to the wrong type of cat.
07-13-2018, 03:36 PM
#20
Launching!
1) You need to work with a competent tuner who can see what your trims are and help you understand why you're making NOx. As mentioned, it's either lean or high temps, but the factory ECU should be swtiching around stoich.
2) If you have a different airbox and MAF placement than stock, the ECU needs to be recalibrated to match. This will greatly help with #1.
3) As mentioned, most aftermarket cats have far less washcoat than OEM. Legally speaking, nothing other than the OEM part number for that engine is allowed. "Green" cats do not meet the letter of the law for this. Less washcoat = less conversion efficiency for both NOx and HC even when cycling around stoichiometric operation as a stock ECU would do.
2) If you have a different airbox and MAF placement than stock, the ECU needs to be recalibrated to match. This will greatly help with #1.
3) As mentioned, most aftermarket cats have far less washcoat than OEM. Legally speaking, nothing other than the OEM part number for that engine is allowed. "Green" cats do not meet the letter of the law for this. Less washcoat = less conversion efficiency for both NOx and HC even when cycling around stoichiometric operation as a stock ECU would do.