# 87 325 Failed NOx Emission Test



## ejsharp (Nov 29, 2004)

My 1987 325 failed Maryland NOx emissions. The readings were:

NOx 3.2379 of max 2.8000 (failed)
HC 1.0949 of max 1.8000 (passed)
CO 10.6681 of max 30.0000 (passed)
CO2 360.0924 max N/A

What can I do to reduce the NOx?

I intend to use high test gas and run a tank of injection cleaner through the engine. Also flush the radiator.

Is there a way to slightly retard the timing in the 325?

Thanks.

Earl J. Sharp
Accokeek, MD


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## The Roadstergal (Sep 7, 2002)

If you still have the original cat on there, chances are you need a new one. Also change the O2 sensor; as it goes, it makes you run rich, which makes the cat fail prematurely. Eurasian has good prices on most parts, including E30 O2 sensors.

Aftermarket ones aren't a good idea, from the stories I've heard of E30 cats; OE is your best option. They're a little pricey, new, but they'll last for over a decade. If you don't want to buy new, check with your local club for racers or people with parts cars. I got an i cat and muffler from parts cars and a guy who had upgraded his i catback in the local club; that was an upgrade for my '86 eta, looked good, and my emissions were ridiculously low across the board.

However, also just make sure your car is running well and all of the maintenance is up-to-date! You don't need any tricks to pass emissions; you just need your car to be happy.


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## ejsharp (Nov 29, 2004)

Thanks but before I throw expensive parts at the car I would like to do something like retard the timing a bit. (which would reduce the NOx)

Any ideas on how to do that? It has a new ox sensor.

Thanks

Earl


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## The Roadstergal (Sep 7, 2002)

ejsharp said:


> Thanks but before I throw expensive parts at the car I would like to do something like retard the timing a bit. (which would reduce the NOx)


No manual timing control on E30s, and you shouldn't have to muck with the timing for the car to pass. If your car is in tiptop shape pre-cat, then that's what the issue is. It's not throwing an expensive part at the car if that's the most likely possibility.  I got mine for quite cheap, BTW - find the local Collectors of Parts Cars...

High NoX might be a sign of running lean, but in the absence of other symptoms, cat is the most likely suspect.


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## ejsharp (Nov 29, 2004)

I agree that the car might be running lean. Will the idle screw enrichen the mixture? If not how can I make it less lean? Maybe cleaning the injectors will allow more gas for combustion.

Earl


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## The Roadstergal (Sep 7, 2002)

There's nothing to be lost by cleaning the injectors. 

You should have some means of checking the mixture before you start playing with the idle screw; check with local shops to see if any of them will do it. Nobody locally would, claiming there was some other reason I was running lean, and that I shouldn't have to mess with the idle screw.

They were right - I had a crack in the boot that went from the AFM to the throttle body.


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## Prov431 (Oct 10, 2004)

ejsharp said:


> My 1987 325 failed Maryland NOx emissions. The readings were:
> 
> NOx 3.2379 of max 2.8000 (failed)
> HC 1.0949 of max 1.8000 (passed)
> ...


NOx is a by product of combustion and there are a few things that you can do to lower it without spending any money if you are simply looking to pass the test and move on.
Lowering available O2 to the F/A mixure will reduce NOx significantly. Cooling the combustion firing temp will also do the same thing (IE: water injection / water mix), and recirculating exhaust gas back to the combustion section (CAT) does the job.
From a simplistic stand point, you could probably restrict air flow without much difficulty and get the results you're looking for.


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## Kaz (Dec 21, 2001)

If the cat's really failed (and it looks like that's the case) the only way you can really screw with the mixture is to fool the various sensors. When the system is running in closed loop (i.e. always except cold start and WOT, generally), A/F, ignition timing, etc. are all regulated by various sensors. Depending on the year/model of the car and engine, these could include, but not limited to airflow sensor, O2 sensor, inteke air temp, coolant temp, etc. A bad cat, along with a bad O2 sensor can easily drive the system wonky, and you can end up spending a lot of time and money trying to tweak things when replacing those two might fit it right away.

That's not to say that tweaking can't make it pass. There are people with euro cars that get their cars to pass emissions testing with NO catalytics by very careful tweaking of various sensor outputs so that the exhaust content is 'right' for testing purposes. It's fun reading about the people who have the time and knowledge to make this stuff work.


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## The Roadstergal (Sep 7, 2002)

Kaz said:


> That's not to say that tweaking can't make it pass. There are people with euro cars that get their cars to pass emissions testing with NO catalytics by very careful tweaking of various sensor outputs so that the exhaust content is 'right' for testing purposes. It's fun reading about the people who have the time and knowledge to make this stuff work.


...and it was much more worth my time to just call around, find a cat from a parts car, slap it on, and pass the test without monkeying with the engine to make it run in a way it wasn't designed to.


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## RChoudry (Jan 13, 2002)

mine failed the NOx also. But my BMW specialist said he didn't think it was the cat.

I'm cleaning the injectors for the next few months and then recheck. He tried replacing the 02 sensor and it still didn't pass.


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## SonTon2003 (Nov 22, 2004)

My DD is in need of the emissions testing this year, I'm scared for her... I am running fuel injection cleaner through the car now (chevron techron), I might replace the fuel filter, I'll make sure to run premium gas, and change the oil. When it comes time for testing they say make sure the car very well warmed up.


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