First off, I have an 06 MS6 and the only mods I have on the car is a CPE CAI, Turbo Smart BOV, & a CEP DP with a cat. Wife went in to test the car and failed on the NOx. Everything else passed with no problems.


A friend of mine said that it is burning to hot and is essentially running lean, causing it to fail. The limit for the NOx is 1.5 and tested at 1.67 ppm. I was wondering if this could have been caused by the cold temps or a heat soaked inter-cooler since she sat for 30 min while waiting to get tested.

If anyone knows what this means and can help me out it would be greatly appreciated. I need to get tags on the car and don't want to spend a lot of time or money.

Hope it's not because the high-flow cat isn't doing enough. It normally has two cats. Would be a bitch to swap out the stock DP and TP just for a smog test though. :\

It's probably due to the high flow cat. I passed just fine last year with only the stock first cat, no second cat.

I don't think it is the cat because the Hydrocarbons passed, CO passed, and CO2 passed which are all primarily due to cat. The emission paper work says that a high NOx readings are "the result of high combustion temps and/ or high combustion pressures"

It has to be the result of some other factor than the cat but what?

It sucks to keep paying for tests, but you could try putting the stock intake and bpv back on and reset the ecu and drive around for a bit to let the fuel trims adjust and then test it again.

erod550 wrote:It sucks to keep paying for tests, but you could try putting the stock intake and bpv back on and reset the ecu and drive around for a bit to let the fuel trims adjust and then test it again.

Yes it does but you have 10 days to re-test for free.

Keep it simple, how long since an oil change? And I would use a can of BG 44K in the fuel tank to get rid of combustion deposits and clean fuel system. Check for vacuum leak(s). Make sure the car is up to operating temp (good and warm) before the next test.

Primary reasons for high NOX:
1 Lean fuel mix - BG 44K will help clean fuel pump injectors and combustion chamber, better than most other products. This may do enough cleaning to unplug the fuel system if it is causing the lean condition. Vacuum leaks fit here too. More air more heat.
2 EGR. The gasses added to the intake side are to reduce combustion temp and NOx. If EGR equipped, is it plugged?
3 Cat. Converter is needed for Nox on non EGR engines.

After that is boils down to defective O2 sensor and PCM (program changes), high mileage engines.......

I do not believe in many pour in "magic" products but have been impressed with BG over the years. I do not own or get paid by BG! If I did, I would not be typing this now!

Heatsoak probably killed you...I bet boost temps where in the 170's after that long a wait.

Yea mine were in that range in the MS3 with an aftermarket TMIC after 20 min of idling at the track so I'm sure the even crappier stock TMIC would have gotten heatsoaked for sure in 30 min of idling. Hopefully next test you can get right in without the long wait, or leave the car off as long as you can before the test. It should still pop right back up to operating temp quickly after only 30 min if it falls below while waiting.

In my last car, after 3 fails in a row, I looked all over for advice and finally passed by doing this:

-added gas cleaner to an empty tank
-filled up with premium
-ran the fudge out of the car for a good 45 minutes before the test
-took out the air filter right before getting to the testing station
-revved the engine as long as I could before test

And I finally just barely passed. Then sold the car to someone who lived in an emissions-free-county...

Thanks for all the input. I believe it was the result of a heat soaked inter-cooler. My wife said that she literally sat there for 30 minutes waiting till it was her turn.

I am also a big believer of BG 44K and will run a can through, change the oil and try to get there first thing in the morning to avoid waiting in line.

Slightly off topic but is BG 44 a good thing to run in an MS3 with about 26K on it? Thought I read somewhere "never add additives to the fuel"

I used it all the time in my other cars....

Running BG44k through a direct injection motor isn't as beneficial as a normal port injection motor. Run a can of Seafoam through the brake booster vacuum line, and you will more likely see better results.

I have to get my emissions done before feb. and I'm thinking I will have the same result, hope not but well see. Seafoam is good shit, I plan on using some before I go in.
Good luck!

Got my emission retested yesterday and passed with flying colors. I guarantee that it was user error that cause the car to fail. It has be awhile since I have had to get emission and forget how dumb the people that work there are.

First off, I pull into the line labeled for AWD vehicles. I wait my turn and am next to pull in when some guy signals me over to another lane. I pull over and roll down my window to ask if this is really where I need to be since this car is AWD and he looks at me like I some idiot. He then goes around to the back of the car and then starts crawling under the car to verify my claim with his buddy, then proceeds to tell me that I need to go back where I was.

Then, on dyno the guy couldn't keep the car under control and it litterally almost came off the rollers. They cancel the run and had to have some other guy get in to give it a try. All while I watch through the window. What a scary mess.