Failed Emissions

[Ezzzzy1]

I had a friend that was going to trade in his 01 Denali and so I bought it for the company and towing etc...

So I took it to get the emissions and it didnt pass

They are saying "high NOx readings

Wondering if anyone has been down this path before? I have read a lot about it and things are pointing towards the cats but there is also information saying the cats will throw codes but its because something upstream is really the culprit.

Also, I put an aftermarket intake on it and am wondering if that could have leaned it out too much and if maybe thats the problem.

Interested to hear what anyone has to say

Thanks all!

[Grim2.0]

What year is it? Does is have NO2 sensors?

[madvlad]

Any check engine light at all?

[Ezzzzy1]

2001 Yukon Denali 6.0

No check engine light but there were some stored codes. "Catalyst system efficiency below threshold"

Normally I would jump all over the cats but like I said I have read a lot about the cats throwing codes because of something on the intake side. Like the MAF sensor leaning the system and that causing the NOx and then the cat throwing the codes.

Grim there are O2 sensors but no codes (faults)

I heard rumor that if you take the car in while the cats are hot sometimes it will pass because they are essentially burning the results? Anyone?

[madvlad]

Could be an intake manifold gasket faulty causing a vacuum leak as well

[bulldog]

Any mods?

My car won't pass emmisions with my headers installed! We live in one of the toughest cities for emmisions....f*ck all their lame rules!

I have passed with a intake though, so that shouldn't be a problem

I've always had to replace 02 sensors to pass, but you usually get a code come up if it is one of those

[rybo]

Having the engine warm helps a lot

Running GOOD fuel helps a lot

running a fuel system cleaner like Seafoam can help

Cleaning the MAF can help

Making sure that you have a good gas cap can help

Giving it an "italian tune up" (flog it down the interstate a bit) can help

[bulldog]

Having the engine warm helps a lot

Running GOOD fuel helps a lot

running a fuel system cleaner like Seafoam can help

Cleaning the MAF can help

Making sure that you have a good gas cap can help

Giving it an "italian tune up" (flog it down the interstate a bit) can help

+1

Most auto parts stores sell special formula to help pass emmisons too.

Usually when they fail you they give you a sheet explaining what failed and what needs to be fixed. Did he not get this?

[Grim2.0]

+1

Most auto parts stores sell special formula to help pass emmisons too.

Usually when they fail you they give you a sheet explaining what failed and what needs to be fixed. Did he not get this?

"high NOx readings

They wont give you a solution for this though.

[madvlad]

2001 Yukon Denali 6.0

No check engine light but there were some stored codes. "Catalyst system efficiency below threshold"

Normally I would jump all over the cats but like I said I have read a lot about the cats throwing codes because of something on the intake side. Like the MAF sensor leaning the system and that causing the NOx and then the cat throwing the codes.

Grim there are O2 sensors but no codes (faults)

I heard rumor that if you take the car in while the cats are hot sometimes it will pass because they are essentially burning the results? Anyone?

Shoot me through PM what the stored codes are and I'll see how I can help you out man

[bulldog]

"high NOx readings

They wont give you a solution for this though.

Doesn't that mean cats are not doing their job then? Maybe a blown out cat as I have heard of that happening; cat is there, but stuff inside is toast

[Ezzzzy1]

Having the engine warm helps a lot

Running GOOD fuel helps a lot

running a fuel system cleaner like Seafoam can help

Cleaning the MAF can help

Making sure that you have a good gas cap can help

Giving it an "italian tune up" (flog it down the interstate a bit) can help

Im going to clean the MAF and get a new cap (even though it passed the test).

Thanks for the info!

[Ezzzzy1]

Shoot me through PM what the stored codes are and I'll see how I can help you out man

Done! Thanks buddy!

[Ezzzzy1]

Doesn't that mean cats are not doing their job then? Maybe a blown out cat as I have heard of that happening; cat is there, but stuff inside is toast

It could mean that but thats where it gets confusing.

So no one really thinks the intake could make a difference? Stock vs aftermarket

[Grim2.0]

It could mean that but thats where it gets confusing.

So no one really thinks the intake could make a difference? Stock vs aftermarket

It could if its sucking in more air and it wasnt "tuned" it could be dumping too much gas in.

I'm surprised the O2 sensors haven't thrown a code, it is possible though that they are both shot and just not doing anything. I cant tell you how many times i had to replace the O2 sensors in my jeep, and i had a after market intake.

[bulldog]

It could mean that but thats where it gets confusing.

So no one really thinks the intake could make a difference? Stock vs aftermarket

I have passed with a AEM Cold Air and I short Ram before.

I've always heard on my car clubs if too much NOx you need a new (or better) cat

[rybo]

It could mean that but thats where it gets confusing.

So no one really thinks the intake could make a difference? Stock vs aftermarket

Intake is more of a "demand" than a supply system. The engine draws the amount of air it needs. If you were adding forced induction of some type I could get behind it being a problem, but the ECU in the car should be able to adjust mixture to cope with any range of intake options, even up to removing it entirely. I'm not thinking it's the culprit.

The other system to consider is the EGR system - if there is a problem there it could cause high NOX, but I would suspect there would be a code in the ECU if that was a problem.

NOX is a result of high cylinder / combustion temperatures. There are a couple of ways that this can happen, and it is the primary reason we've seen the demise of high compression / high performance engines. So, a high compression ratio makes more NOX than a low compression ratio. You can get additional compression by there being a bunch of gunk in the engine taking up valuable cylinder space. Engine overheating can cause it because cylinder temperatures get too high. Too much exhaust gas from EGR can cause it because that air is "pre-heated" -

I would start with good fuel, and some cleaning and a nice drive with some "IT tune up" and take it back. If your number was just a LITTLE outside of the acceptable range then this might clear it up. If it was a lot, then you have to diagnose further, but the most likely cause is a dead catalytic converter.

[Ezzzzy1]

Intake is more of a "demand" than a supply system. The engine draws the amount of air it needs. If you were adding forced induction of some type I could get behind it being a problem, but the ECU in the car should be able to adjust mixture to cope with any range of intake options, even up to removing it entirely. I'm not thinking it's the culprit.

The other system to consider is the EGR system - if there is a problem there it could cause high NOX, but I would suspect there would be a code in the ECU if that was a problem.

NOX is a result of high cylinder / combustion temperatures. There are a couple of ways that this can happen, and it is the primary reason we've seen the demise of high compression / high performance engines. So, a high compression ratio makes more NOX than a low compression ratio. You can get additional compression by there being a bunch of gunk in the engine taking up valuable cylinder space. Engine overheating can cause it because cylinder temperatures get too high. Too much exhaust gas from EGR can cause it because that air is "pre-heated" -

I would start with good fuel, and some cleaning and a nice drive with some "IT tune up" and take it back. If your number was just a LITTLE outside of the acceptable range then this might clear it up. If it was a lot, then you have to diagnose further, but the most likely cause is a dead catalytic converter.

Im with ya and agree. My worry was that the intake could have "leaned" the system but I think you are right, the ECU would have corrected the A/F ratio. Maybe I will re-set the ECU and make sure that its able to get a good base reading.

It was about 7% off (or failed by that much) so I am guessing the handful of things you suggested will work :fingerscrossed:

[jcj81]

if it had a code set in history for Catalyst System Efficiency (P0420,p0430 bank1 and 2) its about 99% chance its faulty converters, if its running lean it will set lean codes P0171,p0174 intake gaskets are common, egr sticking open can cause high nox but egr would set a code for performance if sticking yearly model years had egrs. Mass air flow sensor possible not likely, with out seeing data for fuel trim to make sure its all good I'd go with converters.

[jcj81]

[It was about 7% off (or failed by that much) so I am guessing the handful of things you suggested will work :fingerscrossed:[/QUOTE]

since its just barely out you could have carbon build up just enough to raise temps, do a decarbon let it soak. Older years with higher miles have had slight carbon issues usually will notice slight ping on accel engine at operating temp

[Ezzzzy1]

if it had a code set in history for Catalyst System Efficiency (P0420,p0430 bank1 and 2) its about 99% chance its faulty converters, if its running lean it will set lean codes P0171,p0174 intake gaskets are common, egr sticking open can cause high nox but egr would set a code for performance if sticking yearly model years had egrs. Mass air flow sensor possible not likely, with out seeing data for fuel trim to make sure its all good I'd go with converters.

If you have a minute I will post up the data

[Ezzzzy1]

[jcj81]

So it said check engine light on with both p0420,p0430, you have converters failing. About 100% of the time that ive had those codes its been converter on those trucks

Your short term fuel is normal to slight rich
Your long term is way lean

I think you have bad converters but something is causing them to go bad.

Id say leaking intake gaskets and or skewed MAF sensor. Skewed MAF is hard to see a failure
lekaing intake gaskets if you spray carb or brake clean aerosol around intake you could feel a change in idle if they area leaking or some other vacuum leak

[birchyboy]

How good is the friend? Depending on the county, the seller is required to provide an emissions test.