Failed Emissions - NOx

[mgm1979]

Twice now - limits in Denver area are 1.5000 and I'm currently coming in at 2.13XX...down from 2.58x on the first test.

In between test 1 and 2, I started tweaking my MAF table via standard SD tuning procedures - on average, I was about 1 full point lean, so I've dialed that back in close to 14.7;

With the 2nd failure, I'm debating throwing more fuel at it, at least for the test, to try and help cool things off a little and reduce the NOx some; my concern is that I could richen it up too much and start failing in other categories.

So, my other option is to try and retard some timing??? What's the best way to go about this? Usually, I'm pulling/adding timing based on KR readings and whatnot - pulling timing, almost, randomly has me scared, I guess.

Some local gear heads have suggested pulling boost, but I've run tests and I'm not boosting much, if at all, during any of the emission test program.


Some notes about my setup - I'm currently running a 3" header-back, with high flow cat. GM Stage 2 tune, for the most part, with 60# injectors and a 3" pulley + K&N CAI.
My cooling system appears to be functioning as advertised.

[S2H]

reduce your timing some....that will help...
if you are basing timing on knock then your are doing it the wrong way to begin with...
get some better cats on the car...
high flow cats doesnt mean emissions friendly...
get your pipes welded with a quick switch out set..so all you have to do is bolt up the set you want...
and for that matter have it bolted up as straight pipe...with bolt in cats for emissions

and yes...open the wastegate for emissions....keep it from doing any boost if possible...

[mgm1979]

for emissions purposes, how should I go about reducing timing? I mean, is it as simple (and safe) to reduce the whole table by a point or 2 - or should I just be focusing on the 1500-4000 RPM range that the test will hit?

The cat I have now is flanged, so getting an "emissions" cat wouldn't be that difficult...whether I can have that done in time for the "free" re-test, I dunno.

Bleed any/all boost for the test - check.


So, this will be my "emissions test" tune...

[omega_5]

I agree... pull your timing and try not to push any boost.

When your doing the test, try to keep your temps as low as possible... NOx is generally a product of high combustion temps.

[waynehartwig]

Subscribed... Report back what you do to make it pass - I know I'm interested, even if I'm not failing tests....

[Frost]

Back off timing and get the AFR down. If you are a point leaner than stoich, that's where most of it is coming from. If you get down too far hydrocarbons will rise. A better cat will cut down on those oxides of nitrogen better than a high flowing unit as well.

[mgm1979]

Back off timing and get the AFR down. If you are a point leaner than stoich, that's where most of it is coming from. If you get down too far hydrocarbons will rise. A better cat will cut down on those oxides of nitrogen better than a high flowing unit as well.

I've already got my AFRs down to within normal levels, in the RPM range that the emissions test runs through, which I'm guessing is a credit to the slight improvement from the 1st test.

I'm going to pull out the stock tune and compare the timing tables to the Stage tune I'm currently on - see what the differences are, and see if there's any significant difference in those, before arbitrarily pulling timing in certain ranges.

Is there any way to monitor/measure the NOx levels on my own, without going to the emissions centers?

*edit - timing difference xls attached...I don't think any of that timing block is in the range of the test - the test never gets above 50 mph or so, at a gradual throttle increase.

[mgm1979]

logging confirmed - the Emissions Test is really pretty easy on the engine..Obviously, I'm simulating based on my memory of watching the computer monitor during the test, so I'll bleed ALL boost, just to be safe.

As far as pulling timing though - any ideas on the best course of action in regards to how much and where?