BMW failed emissions - NOx

[JHZR2]

Hi,

Last time I took my car (91 318i with M42 engine, 5sp manual trans) for inspection (6/2003), it just barely passed.

For reference, in 2003, my emissions (dyno test) were as follows:
NOx 1114 (standard is 1134)
HC 97 (standard is 146)
CO% 0.33 (standard is 0.82)
CO2% 14.1
O2% 0.2

So I just slipped by. That test was done with an ProFormance chip installed, M1 15w-50 oil, Amoco low-sulfur premium fuel, and shortly after a tuneup and replacement of the breather hose sets.

Since then, in interest of lowering NOx, I replaced my O2 sensor with an OE bosch. Additionally, thinking that the proformance chip had something to do with it, I bought a Dinan chip for the car, and installed it - thinking this was a name brand that may be designed a little better than my EBAY chip.

The car has been running well. Very smooth, good MPG (29 average), decent power. No signs of an issue, and no CELs or codes. Ive been running on top-tier conoco gasoline currently, with regular use of FP (did a shock dose not too long ago) and LC.

Today I took the car in. My readings were as follows:
NOx 1167
HC 96
CO% 0.35
CO2% 15.3
O2% 0.3

Both tests were performed after a good (15+ mile highway drive) warmup, fast idling while sitting (~2000 RPM), etc.

So my NOx went up just enough to fail me. HC was essentially the same, CO was more or less the same but increased slightly, CO2 increased quite a bit, and O2 increased a tiny bit too.

What do you think? All breather hoses are fine, there is no indication of any leaks of any sort anywhere. Maybe there is a leak on the exhaust after the engine, but I havent seen any evidence of it - usually things like that can be heard fairly easily.

Would use of a chip like the dinan one that Im using cause things like this? If spark/injection timing (thats what chips adjust, right?) is altered, would this cause the potential for hotter combustion and thus higher NOx? The engine doesnt have a knock sensor, so 91+ is mandatory; I always use 93.

As a reference, my 98 Chevy truck (owned since new) had these results on its last dyno test (currently exempted because its an OBDII vehicle, so these are a little old, but done on the same system):
NOx 16
HC 7
CO% 0.01
CO2% 15.2
O2% 0

Based upon the results of the newer, lower mileage vehicle, it tells me that my BMW is:
a) not oxidizing all the CO as it should, as O% ought to be 0
b) CO2 is as high in the BMW case as in the case of my truck, with the BMW having less CO oxidized, and higher HC content. This would tell me that the BMW is running richer than the truck is, and that the cat isnt doing its conversion as it ought to.

Any ideas / suggestions? I NEED to get passed by tomorrow, as I need the car and will be down in DC for the next 4 months.

Thanks in advance for any advice.

 

[benjamming]

On an Accord, cleaning the EGR will usually lower the NOx.

 

[Ray H]

Per benjamming, clean or replace the EGR valve as needed, re-install the factory chip temporarily, and have the car retested. (You DID keep the factory chip, didn't you?

)

 

[jason07-1zzfe]

Don't think it has EGR.

It could just be the cat.

Sounds like the car is maintained. 3way cats convert NOx too.

 

[JHZR2]

Doesnt have an EGR. I was thinking of the cat or the chip, though the chip is 49 state legal and shouldnt be an issue, Id think?

 

[jason07-1zzfe]

Supposedly Dinan chips are same as stock at anything except WOT. So it should not affect emmsion testing.

 

[1sttruck]

NOx seems to increase with combustion temperature, so having a chip and not having EGR will be a problem. No expert on such stuff, but I'd look into backing off the timing advance, if possible, richer mixture at load, etc.

 

[Sam3]

Can you get an extention if the car is out of state?

In general, would removeing the vacuume line to the fuel pressure regulator enrich the air/fuel?

 

[ediamiam]

quote:

---

Originally posted by Jason Troxell:
Don't think it has EGR.

It could just be the cat.

Sounds like the car is maintained. 3way cats convert NOx too.

---

My money is on the cat also. Last time out on my smog check, the technician told me that he suspected the cat on my '93 was losing its efficiency at 130k miles. The initial run was marginal, and he really had to run up the rpms to get it hot enough such that it would pass. I won't know for sure until October, but I now have a new cat, oxygen sensor, and the engine has been auto-rx'd.

 

[eljefino]

Cool 'er down.

Maybe you could increase the % of water in your coolant to around 80% for the summer? Could run 100% and some water wetter.

Even if your temp gauge is "normal" you might have localized hot spots near the cylinder walls. A flush to get crud out might help too.

Too much heat = nox.

Since it seems you only have to go in every other year, you could schedule your coolant changeouts for right before smog time if this works.

I like the idea of cooler spark plugs too.

 

[Terry]

What kind of coil pack do you have, I am more suspect of the ignition coil/coils than anything else.

They can fail slowly and not throw a code while raising NoX to out of control levels.

Analysis should show that trend.

Does this engine have the old above the intake "IAC" valve ? Forget what Bosch calls it.
If that is sticking or failed can cause problems too.

 

[JHZR2]

Well, here is the update.

My earlier test was as follows:
NOx 1167
HC 96
CO% 0.35
CO2% 15.3
O2% 0.3

My test this afternoon was as follows:
NOx 1074
HC 133
CO% 0.34
CO% 14.8
O% 0.2

What has changed? Well, since I could find no leaks, I know the age of the O2 sensor, since I replaced it last spring, and know the operation of the car, I guessed it down to the catalytic converter.

So, while the bunch of you were guessing that it was the cat, I was having it replaced

NJ required $450 worth of spending before a waiver will be granted. I spent $250 to have a generic high-flow converter installed by Meineke. Surely not the best, but I figured it was worth a shot, especially since Id have to spend some $$$ before they'd waive my test requirement anyway.

So same day, after a highway drive and then an attempt to find the inspection station (couldnt go to the same as before), I got it checked, and it passed. All is well for 2 years.

Terry, my UOAs have looked good to me. Ill have one for you, for this car, within the next month. Thanks for the tips.

JMH

 

[Winston]

That does not seem like much of a change with a new Cat. I would have thought there would have been a bigger reduction.

 

[JHZR2]

me too... tells me that either its operating at its design point (which some data from other owners points me to believe is sort of the case), but at the same time, something may be a bit out of tune, at least to some small extent... not sure.

One way or another, I can rule out O2, can rule out Cat...

maybe there are some CC deposits that top tier fuel and FP/LC arent cleaning. Maybe I need to do the MMO in gas treatment?

 

[ediamiam]

Compared to a '93 Mazda 626 w/ 6 cyl at 130K in 2003 at 25 mph: Max allowable NOx is 746 California. Good thing yur not stuck in California

------Yurs--Mine
NOx 1074 84
HC 133 27
CO% 0.34 .05
CO2% 14.8 14.9
O% 0.2 .1

 

[nel]

Unfortunately, the conversion efficiency of the generic cats are not the greatest. It's strange that the HC actually increased in the second run. Usually, a new converter should bring the HC down dramatically. Glad to hear you passed.

I'm planning on changing out the converter on my '90 325is next year with an OEM one (and while I'm in there, I'll do the guibo, driveshaft center bearing, and shift linkage).

 

[JHZR2]

Interesting about the conversion efficiency. Id have to guess that in order to hit the price point, that the generic converters have less catalyst loading on the monolyth, and/or that the monolyth has larger holes, and as a result less surface, which is the name of the game in catalysis.

IO figured the $250 would get me over the hump, had the situation arose that I needed to hit $450 in repairs for a waiver.

My muffler is starting to get a little rusty around the hanger straps. When it gets a hole, Im planning on doing and OE cat, and then the whole cat-back, all with OE parts. BMW exhausts cant be very much improved upon, at least not on the M42 engines...

Thanks!

 

[Drew99GT]

Timing advance usually lowers combustion temperatures, well, up to a point. Perhaps the chip is leaning out the fuel too much or advancing the timing so much that the knock sensor is taking over. That would raise combustion temps.

 

[Jimbo]

O2 never goes to zero, except WOT, because, chipped or not, engines are calibrated to run lean-of-peak part-throttle mixtures.

Since the reduction cat (NOX) is aft of the oxidation cat (HC&CO) in the exhaust system, and they are both pretty far back from the engine, the car needs to be really hot from a high speed run right before the test.

 

[nel]

Unfortunately, a great number of older BMWs are having issues with passing emissions. The '90 325is I bought recently failed California smog twice. And, you hear about all the woes other e30 owners have on the BMW forums.

Valve lash is critical so you may want to check that. I've heard of others trying the CRC Guaranteed to Pass with some success, and you're doing the right thing by using 91 octane gas. NOx is a function of high combustion temperature. There's not much we can do on these BMWs to lower the temperature, though. Your performance chip shouldn't change the spark advance at the engine speeds that the emission test takes place at. Finally, your cat may just be too old and may be due for replacement. The previous owner of my '90 e30 paid $100 to a muffler shop every two years when it was time to have the car smogged. Even then, the car only passed marginally.