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  #1  
Old 11-18-2004, 01:30 PM
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High NOx in 87 BMW

Please excuse this transgression. My wife's 1987 325 BMW has failed the Maryland NOx emission test which uses the tread mill method.

The reading are:
HC 1.0944
CO 10.6681
NOx 3.2379 (2.8000 is passing)
CO2 360.0925

I am told by our neighborhood gas station that I should blow out the engine with some fuel injector cleaner and then take it directly to emision control for a retest.

Idle speed is set by computer but there is an adjustment screw that can affect the idle speed... it appears to regulate the air to the intake manifold. How do I make the mixture richer (less lean)? By increasing the idle speed or decreasing it?

I was told by one mechanic to lower idle speed from 900 to 700 and by another to blow out the engine with fuel injector cleaner. (Car failed a second time at 700 RPMs from 900 but NOx improved by .5)

All hoses are tight and there are no leaks. Car probably has regular gas in it.

Can anyone tell me what to do? I did not yet blow out the engine with fuel injector cleaner.

Also the car has high miles... 275,000. Would a radiator flush help?

Thanks.

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1993 190E 2.3
2000 Toyota 4x4 Tundra
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Old 11-18-2004, 01:42 PM
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If the initial timing is adjustable, retard it 6-8 degrees from spec. If it has an EGR system, check it for proper operation.

You don't need fuel injector cleaning, and idle speed has little or no effect on HC or CO emssions on the IM240 test, and NO EFFECT on NOx emissions.

Visit the current emission discussion threads for some more insight. They're obvious from the titles.

Your car was tested on a device called a chassis dynomometer. The term "treadmill" is used by state bureaucrates who think the people who pay their salaries are idiots and can't understand "big words".

Duke
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Old 11-18-2004, 02:08 PM
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Thank you Duke... I was hoping to hear from you. There is no adjustment on the timing and there is no EGR valve.

I read the previous discussion that you participate in but I am at a loss in figuring out how to lower the operating temeratures of the engine. Nano ice cubes have not yet been invented.

Blowing out the carbon and using high test seems practical and a common sense solution but I just don't know. I am asuming the BMW has a high compression engine (therefore my high test proposal) and I believe the injector cleaner's purpose is not to clean the injectors rather it is to help blow out the glowing carbon deposits of the high milage engine.

Can you dig down for an alternative solution?

Thanks again.
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1993 190E 2.3
2000 Toyota 4x4 Tundra

Last edited by ejsharp; 11-18-2004 at 02:50 PM.
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  #4  
Old 11-18-2004, 05:00 PM
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Dynomometer

P.S.

Your absolutely right Duke... I thought a dynomometer measured dynosores.

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1993 190E 2.3
2000 Toyota 4x4 Tundra
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  #5  
Old 11-18-2004, 08:43 PM
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NOx has nothing to do with engine operating temperature as expressed by coolant temperture. NOx is created in the combustion flame front which runs about 4000-4500 degrees F.

For every engine speed and load there is an ideal ignition timing that will create maximum thermal efficiency, which means lowest fuel consumption. This, unfortuately is also the timing that creates maximum flame temperature, which also produces maximum NOx.

OEMs have to walk a fine line between NOx standards and fuel efficiency, so depending on the model, igntion timing may already be slightly retarded from the ideal amount that would maximize efficiency. Retarding from this point further reduces peak combustion temperture and increases EGT. The former will reduce NOx and the later will usually reduce HC and CO, so retarding the timing is a quick way to turn a marginal failure into a pass. Sometimes only a drop of a couple of hundred degrees in peak flame temperature will reduce NOx significantly because there is a "knee" in the reaction rate curve at about 4000 F. Above this NOx can increase dramatically. Likewise, below the knee in the curve NOx is relatively low.

Modern cars are becoming more "tamper proof", and this includes eliminating the option to vary initial timing or the rest of the timing map as established for engine speed and load. Such is the case with many Mercs. For example, on the M103 engine we can't adjust the initial timing, but changing a plug-in resistor will slow the rate of timing advance with engine speed and there may also be a chance that vacuum advance can be eliminated. Either of these will reduce the timing that the engine sees during the emission test and should reduce emissions.

Since I'm not familiar with the igntion systems on BMWs I can't give you any guidance on how to reduce your timing, but I would imagine that there must be some BMW discussion boards with someone sufficiently knowledgeable about the BMW ignition system to have figured a way.

That's the best I can do on this one.

Despite the fact that field emission testing has been in place in many parts of the country for over 20 years, there seem to be few techs who understand how emissions are formed, how they are controlled, how an engine can be "adjusted" to correct a marginal failure, or even read the test data on an emission report and use it as the beginning point in a diagnosis. Instead, they mostly want to sell you "tuneups" and "fuel injection service" or other services that are profitable for the shop, but often don't get at the root cause of the emission test failure. I'm glad that the CA test reports O2 content, because it is an important diagnostic tool that can get one started in the right direction toward solving an emission problem.

Duke
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  #6  
Old 11-18-2004, 09:59 PM
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High NOx = Car running lean.
Find reason why.
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Old 11-18-2004, 11:38 PM
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If it was lean enough to bust the NOx limit the CO would probably be lower.

What was the CO test limit?

Duke
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Old 11-19-2004, 12:14 AM
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The CO test limit is 30.000 and car had 10.6681. Limit for HC is 1.8000
test was 1.0949. Limit for NOx is 2.8000 and test was 3.2379.

Thanks for that knee information.
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1993 190E 2.3
2000 Toyota 4x4 Tundra
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Old 11-19-2004, 01:11 AM
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I don't think the high NOx is due to a lean condition. Running a little richer might help, because you have a some HC and CO margin, but you have no control over the mixture. It's never a bad idea to check O2 sensor output. On my 2.6 I can pull out the O2 sensor signal lead connector (under the passenger footwell carpet) enough to get a scope test lead on it and eavesdrop on its output. This way the O2 sensor is still connected, so the test setup does not disrupt the operating circuit. I look for the signal to jump back and forth between about 0.2 and 0.8V at a frequency of about 0.5 to 2.0 Hz.

Wish the IM 240 test results included O2. The O2 content is a good diagnostic tool on the CA ASM test.

BTW, what are the most recent emission test results for your '87 300E.

Duke
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Old 11-19-2004, 01:13 PM
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On 22 september the 300E tested at:

1.1907 HC with a ceiling of 1.8000; 4.6981CO with ceiling of 30.000: 2.6627 NOx with a ceiling of 2.8000 and a CO2 reading of 431.2910... no ceiling for CO2.

On the BMW I think you may be right about the need for a richer mixture. I supect however that I may be able to tweek the NOx by increasing the idle speed to a setting above 900 rpm.

The car idled a little over 1,000 rpm after I changed the oxygen sensor and I then turned the idle screw so that the car idled at 900 rpm. It failed IC NOx so I lowered the idle to 700 rpm. It failed again. The manual says that the idle screw does not set the idle speed and that it should not be messed with because the computer will regulate idle speed. Therefore I suspect that the amount of air that the idle speed screw allows into the intake manifold is constant for the entire range of RPMs. The idle setting allows a controlled amount of air to bypass the air intake and then feeds that positive or negative air flow for combustion.

My next question is which way do I turn the screw and do I want more or less air to the combustion chamber.

Also, on the BMW, I can do exactly as you did on your Oxygen sensor test... ie feed thin wire probes into tne wiring connector and get a reading on the behavior of the sensor. But I only have a volt/amp meter and not a scope. My neighbor has a tester that is a bit more sophisticated but not as good as an ocilascope. I forget exactly how his tester works.

Here is a complete history of the failed tests:
Limit: HC 1.800 CO 30.000 NOx 2.8000 CO2 N/A
2 August- HC .7510, CO 12.1352, NOx 3.7898, CO2 349.9235

I then changed oxygen sensor and set idle to 900 using adjustment screw that should not be used to set idle speed. Retested vehicle:

20 August- HC 0.7891, CO 9.7136, Nox 2.9853, CO2 351.7512

Car failed so I lowered idle speed to 700 using the adjustment screw that you are not supposed to use. Results:

26 May- HC 1.094, CO 10.6681, NOx 3.2379, CO2 360.0925

Hope you can see something in these results.

Many thanks.
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Old 11-19-2004, 02:31 PM
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NOx is produced primarily during cruise and light acceleration at the controlled stoichiometric A/F ratio. Very little is produced at idle or at WOT if the engine has full load enrichment, which most do, but WOT would not be required on the IM/240 test unless the car is severely underpowered, which would not include a 325i. Thus the idle speed setting has little or no effect on NOx. Even a small vacuum leak will be compesnated by the control system as the O2 sensor will detect a lean mixture and richen it to maintain stoich. until it reaches its limit of control authority.

I don't know the details of the 325i idle control system, but most have an adjustment that should be set to a nominal idle speed value with the idle control system disabled. On the M103 engine this is the throttle stop on the throttle valve shaft under the fuel distributior. If this initial setting is too far off the system may not have enough control authority to maintain proper idle speed. As a rule, one should not mess with this initial setting unless you have proper service documentation and equipment to perform the procedure properly.

The fact that you replaced the O2 sensor means its probably not the culprit and the change did not affect the readings that much, so the old one was probably okay. It would not be unusual to test the car twice in two days and see readings at least 10 maybe even 20 percent apart.

There's another issue that most car owners aren't aware of. Test standards are being continuously lowered, and established test standards have no precise correlation to original certification standards. It's possible that your car is functioning perfectly less some degradation of emission control components such as the catalyst. This is an issue you have to bring up with your state emission test authorities. If they are like CA, they may be uncooperative, in which case you should contact one of your elected representatives. I have and will undoubtedly do so in the future.

Questions you might ask are:

What are the average emissions for this year and model car?

How do the test standards correlate with the original certification standards? How much degradation is allowed?

My 190 is on the ragged edge of HC emissions, but is relatively low on NOx, and most M103s tend to follow this pattern. In fact, in the three ASM tests my car has had, the measured NOx and standards are all over the map, which leads me to believe that the measurements are somewhat suspect. I know that when CA first implemented the ASM test, which added NOx measurement, the standards were quite high, but they have been lowered a few times since then. But the real issue is why the measured amount has gone down so much. Leads me to suspect that the measuring technology is far from foolproof.

Duke

Last edited by Duke2.6; 11-19-2004 at 02:38 PM.
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  #12  
Old 11-19-2004, 10:07 PM
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Other possibilities for High NOx:

Malfuctioning/Inoperative EGR valve, Out-of-calibration MAP sensor, plugged injector, low fuel pressure, vacuum leak, advanced ignition timing.

Any of those malfunctions will cause higher internal temperatures, hence increasing NOx.
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  #13  
Old 11-23-2004, 12:45 AM
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I noticed that my adolecent son had fooled around with the air meter system and had knocked off and lost a cover to a gadget (Mounted to the outside of the air filter cover) that has a small pointer inside of it. (It may be damaged but if so the damage is not obvious) That was over a year ago.

I made a new cover for it.

I mention this because I don't know what a MAP sensor is and I don't know what my son may have done to the car.

Is there a way I can check things out?

Thanks.

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1993 190E 2.3
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