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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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

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

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.

__________________
Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

P.S.

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

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

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

High NOx = Car running lean.
Find reason why.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

If it was lean enough to bust the NOx limit the CO would probably be lower.

What was the CO test limit?

Duke