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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Fri, Apr-02-2010, 10:03:17 PM   #1
ken97e36
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Default SOLVED: Need help from emissions experts - High NOx reading

Hi all...just picked up a 97 M3 but can't get the car to pass emissions; here's what's been tried so far:

First run: pretty much right after I picked it up (I bought the car remotely and had it shipped to me). Had old gas in it (probably 6+ months) but almost empty. Results:



After that, ran the tank way down, put in 58 litres of 94 octane (15.3 gallons) drove around for an hour or so (normal driving). Went back a couple days later, got an oil change. Retested (though the car had been sitting for about half an hour). Results:



I've read a few things about what to do if you're getting High NOx readings:

High Nox Only

* NOX is caused by high combustion chamber temperatures. Check:
* EGR (valve, controls, solenoids, passages, vacuum hoses)
* Ignition Timing ( base and advance)
* Engine Temperature (cooling system, fan restricted exhaust, Thermostat)
* Vacuum Leaks (hoses, booster, evap, etc)
* Mechanical (carbon deposits, converter, etc)

I'm not a mechanic, so I don't think I'd have the know-how to test those things myself. Is it hard to get at the EGR valve? Could I check it myself?

I also know that I could run the car on the highway for an hour or so and do the emissions test right after when the cat is sure to be super-hot. But I'm not confident that that will drop my NOx emissions by that much. I'm trying to avoid getting a cat. Another thing: The car passed BC emissions in Vancouver 7 months ago, after which point the car was put in a garage and not driven. So I doubt the cat could have gone from good to failed after 7 months in a garage. However, Vancouver does use a different measurement system than Ontario. Here are the results of that test (August 2009):



and the previous one in 2007:



I've noticed the NOx readings increased between those two tests; however, after August the car wasn't driven, so I don't see how it could've increased between then and now. Also, couldn't the increasing NOx emissions be the result of an increasingly clogged EGR valve?

Any advice would be appreciated.

Last edited by ken97e36; Sun, Apr-11-2010 at 09:45:31 PM.
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Old Sat, Apr-03-2010, 11:54:11 AM   #2
Richardsperry
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Me? I'd change the (2) precat O2 sensors, and spark plugs.

Clean the HFM, and throttle body, and look for a vacuum leak. Check the easy stuff, intake boots, ICV, FPR lines...
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Old Sat, Apr-03-2010, 12:36:09 PM   #3
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I would bet you need a cat.
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Old Sat, Apr-03-2010, 12:49:56 PM   #4
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Like the second post ideas, but not sure if O2's would do much for you or not, maybe, also make sure the cats are as hot as possible, as they come up to temp is when they work for reducing NOx, can't remember for sure but I believe around 900 degrees F is when they start to work on breaking down NOx.

Perhaps a fuel additive to help reduce carbon build up?
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Old Sat, Apr-03-2010, 03:32:28 PM   #5
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Common problem on cars with no EGR valve (e.g. BMW's) is high nox emissions. BMW don't have an EGR as part of the emissions controls, so when the catalytic converter gets a little old it's a little harder for it to clean up the emissions.

Let me explain a little bit on what NOX actualli is. NOX is formed when the temperature in the combustion chamber gets hotter than 2500 degrees. This is caused by a lean running engine or high compression , which is caused 95% of the time from carbon buildup from poor gas, (or in some rare cases a head job where too much has been machined off the head and the proper head gasket is not used, therefore increasing the compression but I doubt that's your case.)

BMW's don't have much to clean up those emissions other than the catalytic converter, which should be the last thing you should replace because it's the most expensive. Your car isn't running lean because your co is at 0.03, and you don't have any codes for O2 sensor so don't bother changing that.

Heres what I recommend...
1) If you have been using cheap gas (I don't know what you guys have there in canada), buy some sea foam engine carbon remover, and follow the directions. Theres 2 ways to do it, don't put it in the gas tank. Feeding it to your intake via small vaccum leak is the most effective way. If you do this step, make sure you drive 40-50 miles after your done to clean out your engine and cat.

2) Your catalytic converter works best when it is as hot as you can get it. Before you take it in for the emissions test, drive it around 10-15 miles, using 50-75% throttle occasionally to warm it up. Now important part. Make sure there is nobody ahead of you when you take it in for the test. Just park outside and keep your car in neutral and 2500 rpm for a minute or two to warm it up VERY good. Drive in and get it done as soon as you can, the hotter your cat, the lower the readings.

GOOD LUCk
BTW, if that doesnt work, you need a new cat
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Old Sun, Apr-04-2010, 01:46:51 AM   #6
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+1 on suspecting a cat. Usually the NOx culprit on cars with no egr. I've also seen biased O2 sensors cause this. Or a lean condition from a vacuum leak, or exhaust leak before the cat. I'm looking at buying an m3 from western Canada also.
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Old Sun, Apr-04-2010, 10:57:23 AM   #7
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the car could be running too hot. you can try removing the thermostat for the test.
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Old Sun, Apr-04-2010, 06:38:07 PM   #8
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take it to a shop and get everything checked as there's too many variables that could cause this. a decent shop with a good tester would be able to see what your all sensors are doing in relation to each other and determine from there the root cause of your problem
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Old Mon, Apr-05-2010, 11:55:19 PM   #9
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Thanks for all the responses. I didn't mention that the car has Dinan stage 1 software installed. My mechanic thinks that's the issue, though from what I read that shouldn't be the cause.

I'm thinking of trying a used OEM cat with 75K miles for $200. This is far cheaper than an aftermarket system would cost me.

However, before I do, just one more question. I've read of people posting that they are getting CELs indicating the cat efficiency has dropped below threshold (P0430, P0420). If my cat is failing, why am I'm not getting any CELs? (I used an OBD tool to check that there were no codes, so it's not just because the light on the dash is blown. )
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Old Sun, Apr-11-2010, 09:45:16 PM   #10
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Just wanted to post a final conclusion to help out anyone else that might be looking for help with emissions. After the OEM cat was installed, here are my e-test results:


Looks like it was the cat after all.

Thanks for the help, everyone.

Last edited by ken97e36; Sun, Apr-11-2010 at 10:08:42 PM.
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Discussing Need help from emissions experts - High NOx reading in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)