Failed my Calif. smog test today,,any ideas ??

[Chris'91'525i]

So I failed my Calif. smog test today by a small amount.

They run the test on a treadmill devise to simulate road speeds.
Emission are tested at 15 & 25 MPH. I failed HC and NOx on the 15 MPH test. HC max allowable is 108 ppm I came in at 113 ppm. NOX max is 767 ppm, I came in at 1066 ppm.
Max CO % is 0.71, i came in at 0.22%, so that's OK....

The 25 mph test passed with flying colors. I ask who the hell drives around at 15 mph ? OH, it's probably the bumper to bumper traffic on CA freeways during the rush hours :)

Any ideas what is causing the high NOx emissions ?

The car has had a complete tuneup and a new Cat installed in the last 8 months. All the cylinders have high and equal compression, was tested at the tuneup.
Car runs great and idles rock steady at 6-700 rpm......
Drove car 15 miles before test, at upper RPM's to get it good and hot.

How are NOx emissions controlled in a M50 engine , since there is no EGR ?
Is the NOx controlled by valve timing ?

Only thing I can think of, is they put a 2 way instead of a 3 way cat converter on the car. And fudged on the last emission test. Or it's just some crappy cat that got installed....

Any ideas guys ??

Boy, I sure envoy you guys that don't have to go though this emission testing BS !!

[Gayle]

Wow. I would be really PO'd if I failed with a new cat. Bummer.

We had high NOX readings on the 525 we used to own.



Here is what Bill R explained about that.


Nox is caused by high combustion chamber temperatures, typically high performance cars with large lift cams and high compression also had very high levels of nox. Anything you do to reduce the amount of energy being produced will lower your nox levels. If your running regular instead of premium your nox will be higher since theres more energy being released in regular since it burns more rapidly, so running premium will make a little difference. Running the 10% ethanol blends will also help since this reduces the amount of power in the fuel also. which will lower combustion chamber temps. The cat is going to make the biggest difference, so make sure its completely warmed up and don't shut it down any longer than needed while waiting to be tested.


Our NOX problem was really bad. Allowable Max is 767/706 Our car 884/1124. I got it down over 50% and passed so there is always hope. Here is the whole thread.

http://www.bimmer.info/forum/showthread.php?t=12713

This other current thread has some good suggestions:

http://www.bimmer.info/forum/showthread.php?t=26432

I am not sure anyone ever knows why a car fails. You just throw every trick in the book at it and try again.

[Chris'91'525i]

Thanks for that info Gayle..
Yeah, I'm kind of PO, with the numbers being so close to passing ..... I'm thinking now I got some bad petrol, or was pumped the wrong grade.
I filled up with "premium" at ARCO the other night. Even though it seems to run as good as always, the close to passing numbers make me suspect weak octane gas.
Damn, the one time i didn't fill with Chevron !!
Maybe get a bottle of octane booster, and try it again.

[Gayle]

My husband had it worked out with the smog place that they would take the car in as soon as he drove up so the cat was still really hot. You might talk to your place to see if they would do that for you.

[DABLACK]

I just went through the same thing in Sept. I flipped out of course but after i settled down changed the the oil and the spark plugs took it back to the test facility and BAM! It passes like the was nothing wrong to begin with.
I hope you situation is the same but maybe start small and see what happens and like Gayle says keep it HOT!

Good Luck!

[DABLACK]

SORRY!!!!!
i also forgot I cleaned the throttle body chemi reccomended by one of the master tech's at the dealer I work at

[BillionPa]

couple of things... as part of the tuneup, was a new O2 sensor part of it? you may also have a vacuum leak somewhere that gets sucked shut at higher rpms.

in terms of getting the car better for emission standards, find a terraclean dealer somewhere, that works really well.

also acetone reduces SOME emissions (massive hydrocarbon reduction after a few weeks of use), but i have no idea how it would effect nox levels... i should get my car tested for kicks.

if you are running 40 or 50wt oil, throw 30wt with low additive levels in there for the test, then dump it when you are done. (probably not necessary)

your plugs should be ok of 8 months old (i hope), but ignition coil(s) arent generally on the standard tuneup list, and if yours are over 7 years old, they dont burn as much fuel, so you will get higher emission levels