failed NO emmissions test
 

Trying to figure out what causes to fail the NO (ppm) test on my kid's TOYOTA 1987 MR2

%CO 14.6 & 14.7
%O2 0.3 & 0.2
HC (ppm) 33 & 25
CO (%) 0.01 & 0.03
NO (ppm) 1115 & 735 max 825 & 764
failed the 15 mph test and barely passed the 25 mph test.

I also was told that the timing was of by 10 degrees, retarded I think but not positive.

Don't know what causes the NO emmisions, the cat was repalced two years ago, the car uses a quart of oil every 1k miles.:confused:

Check to make sure the EGR system is working. My guess would be a leaking EGR vavle.

I'll check that, anything else???

failed NOx emission test
 

The oil consumption has probably killed the catalyst. The phosphorus in the oil (antiwear additive) is a permanent poison. 1qt/1000 miles is a LOT of oil consumption for that small engine.

You MIGHT try a high speed/high load 'burn-off' attempt on the catalyst before changing it. Also be sure the timing is right on, the EGR valve, plumbing, and passages are clean and working properly.

High NOx readings mean combustion temps are too high. EGR reduces combustion temps so start with that. If the spark timing was 10-degrees too advanced that might contribute to high combustion temps as well.

The folks at www.club4ag.com might have specific information.

Sixto
95 S420
87 300SDL

Thanks for your replies, what do you mean by high speed high load burn off? 1 hour drive or longer?

The cat was replaced 2 years ago but I see what you mean.

I will take apart the EGR system and inspect it well.;)

If the engine has EGR check the valve function and control system.

Also, properly check and understand what the timing is relative to spec. You may have to short a couple of leads on the diagnostic connector to get a true initial timing value. Look on the emission control decal or get a shop manual. The timing is supposed to be measured as part of the test and recorded on the report.

Retarding the timing will reduce NOx since it reduces peak combustion temperature, and the CA inspection places no limit on how much the timing can be retarded from OE spec.

I doubt if there is anything wrong with the catalyst given the low HC and very low CO.

Duke

running lean
 

%CO2 14.6 & 14.7
%O2 0.3 & 0.2
HC (ppm) 33 & 25
CO (%) 0.01 & 0.03
NO (ppm) 1115 & 735 max 825 & 764

CO2 is relatively low comparing to a very good engine, EFFICIENT AND COMPLETE COMBUSTION (15.2 TO MAX 15.6).

O2 is high and CO is very low indicates lean mixture. Low CO may also leads to low catalyst converter efficiency. Air leak past the air metering stage?

great information, thank's.
Now what to do about it?

Check the spark plug. If the insulator is white and/or blistering (normal is light tan), the engine is running lean and hot.

Possibilities:
Air duct leaking from air metering device to the intake manifold.
Leaking intake manifold gasket.
Throttle plate shaft leaking (loose).
etc., etc

Search the archive for leak detection techniques.

Ok, I will start by looking at the EGR valve and plugs.

egr valve and tubing good and clear, plugs white deposits.
running lean.

Juan,
I concur with all the above comments and advive so no sense repeating. EGR is the major contributer to reducing nitrous oxides and nitrogen dioxides, so be sure the system is funtioning. Apply vacuum to the valve at idle and make the engine run rough or die. Then hook it all up and observe that the EGR needle moves as you race the engine. You can tweak CO up a bit and that will also help. If you have an air pump, it plays a minor part, so make sure it works. Also be sure you are using the grade of fuel the car calls for. If the car calls for premium, combustion temps will increase with faster burning lower grades. All in all I thought those readings were good across the board and NOX isn't that far off. In fact I had a 90 300SEL in the same boat last month and tweaking the CO up got it through.

Good luck,
Peter

Thanks Peter, the car does not have an air pump. I will check the timing which I should have done before I took the EGR system apart.
How do you adjust the CO?

I will also fill up with higher grade gas. I have the "cheap stuff" in it right now. No such thing in the Bay Area as you know.

Sorry Juan,
I know nothing about Toyotas. We pay more for gas than anyone in the country. When they were doing live reporting on that DC serial sniper, I wasn't paying any attention to the reporter. My eyes were fixed on the Shell station behind her with the rediculously low prices.

Peter

Peter, I know just enough about cars to be dangerous. I will go and buy a can of ether and after I put the stuff together I will start it up and spray ether at the air possible leaking places and hope for it to speed up. I remember using that tecnique in the past.

One more question regarding the MR2.
The spark plugs were white instead of tan color, if the car is using more oil than it should 1qt per 1k miles, shouldn't the color of the plugs be black from burnt oil instead of white?

Hope the oil usage is other than through the rings or valve guides.

High NOx often indicates lean mixture, as you are suspecting. The mixture can be adjusted on many FI systems. May not get at the root cause, but may get you past the test.

today it was tested again, NOx 822 max 825.
changed plugs, and put a tank of 91 octane gas.:eek:

Congrats, Juan,
I'm sure the high octane slower burning fuel helped reduce NOX because of the lower combustion temps. Hey, I'm not making this up. It is well documented.

Peter

Thanks Peter, the car runs better with the better gas, may need to keep fueling with 89 octane from now on.
Now I can concentrate on the 300E. Finally.:D

I'd like to see some of the "documentation" and sources for this claim.

Duke

Duke,

If you happen to have a friend in the smog business, ask if you can curl up with some of his books that come with his machine or any of the course books he may have that helped him get his license. These books are loaded with theory, explanations and graphs showing relationships beween the 5 gas readings and temperature. Used to be CO and HC were enough. Now you have to look at CO, HC, O2, CO2, and NOX to diagnose cars.

Peter

No, but I have a MS from the U. of Wisconsin Engine Research Center where I did emssions related research, and I refute an claims that commercially available gasolines have a significantly different flame propagation rate.

It's a myth!

Duke

Then why are there different grades of gasoline? why not just one? Why crack gas at different grades?

Peter

The basic difference between commercial gasoline grades is octane number, which is a measure of the fuel's resistance to detonation. Higher compression ratios need higher octane, but deliver higher power across the rev range and greater fuel efficiency.

During "normal combustion" flame propagation rates for fuel-air mixtures of a given ratio and density are about the same. Detonation is "abnormal combustion", and since the unburned portion of the F-A mix ignites spontaneously and completely rather than being consumed by normal flame propogation this may be the source of the myth than "premium gas burns slower".

Duke

Engine operating temperature is often overlooked as a contributing factor to high NOX output. A ten degree increase in engine temperature will affect NOX output by a certain percentage. Duke2.6 may be able to shed more light on this particular area of combustion science. Suppose your radiator has low flow, on your temp gauge you see no real visible signs until you decide to pull a steep grade. When you begin your ascent you begin to notice the temperature increase and in most cases you may dismiss it because you are climbing a hill. The radiator may be flowing 70% to 80% of the volume it was designed to flow. Because it is so gradual over time as a driver you begin to unknowingly adapt to this gradual increase in operating temperature. In some cases a new t-stat, a new temp switch, or a new radiator (maybe a combo of any or all) will have more impact at reducing NOX than what is often considered.

This assumes that you have eliminated primary contributors and or emission components/devices that are responsible for either increasing or decreasing the overall NOX output. (Engine timing, EGR Valve & control, Catalyst, etc warrant that a technician may need to verify their correct operation before reaching a conclusion)
:cool:

Coolant temperature has little to do with NOx. NOx is produced in the 4500 degree flame front, and there is essentially no difference in flame front temperature (for a given set of operating conditions) within the normal range of coolant temperatures. The higher the flame front temperature, the greater the NOx produced, and there are strategies to decrease engine-out NOx to a level that will be acceptable at the tailpipe after further reduction reaction in the catalyst. (I use the word "reduction" in the chemistry context. It is the opposite of oxidation.)

Higher coolant temperature mean hotter combustion chamber boundaries, which reduces flame quenching at the boundaries, so engine out HC is usually lower with high coolant temperatures.

Spark timing has a big impact on both engine out NOx and tailpipe HC emissions. For every operating condition (speed and load), there is a timing value that both maximizes torque and minimizes fuel consumption. This "ideal" timing will also produce the greatest flame front temperature and NOx, especially under "lean" i.e. stoiciometric condtions, so timing under many operating conditions is decreased below the ideal to decrease engine out NOx. Retarded timing also increases EGT, which helps keep the converter hot enough to generate good oxidation and reduction efficiency to decrease engine-out emissions to acceptable tailpipe values.

The "ideal" timing is that which produces the greatest thermal efficiency, and greater themal efficiency requires adding heat at higher temperature, but if NOx is too high, timing must be retarded. This essentially reduces the fuel's contribution to useful energy at the crankshaft and throws more energy out the exhaust, which, of course, increases fuel consumption.

The other strategy to control engine-out NOx is EGR. By diluting the fresh charge with an inert gas, peak flame front temperature is reduced.

A simple stategy that car owners can use to reduce both NOx and HC on a car that may have marginal emission test performance is to retard initial timing. Retarding the timing reduces peak flame front temperature, which reduces engine out NOx. Also, the higher EGT from retarded timing will keep the converter hotter, which will increase its oxidation and reduction efficiency.

Unfortunately this is not an option on many Mercedes models because the intial timing is not adjustable - like my M103 engine.

Duke

Let me share a real world experience with you and you may have a different perspective.

1979 450SL-Failed NoX, you name it was done. Any and all items that you could possibly install to correct the matter simply did little to bring the NoX down. After my friend spent many hours on the vehicle I suggested he take for a nice long drive to see how it would clean up. As luck would have it we have a good selection of decent grades here in the bay area, so off to Santa Cruz. Half way up the hill the engine temp was hovering at 100 C, way too hot for a 65 degree day.

Long story short- the radiator was flowing less than 60%. Installed a new raditator and the NoX fell to the basement.

2100ppm before the rad, <400 after.

Engine temp is something I now consider based on this experience.
:cool:

Interesting anecdote, but there had to be some other factor at work. For example, above a certain high coolant temperature, some emission control configuratations will restore vacuum advance at idle and low speed/load and/or suspend EGR, both of which will increase NOx. That's just an example. Since I'm not intimately familiar with the emission control equipment or configuration of that engine, I could only hazard a guess, but engines of that era had all kinds of klugy emission control hardware that can be a nightmare to sort out.

As a general rule for emission testing you want the engine as hot as possible. A change in operating temperature within the normal range - say 80 to 110 C will not cause that dramatic a change in NOx unless the high temp disabled the NOx control features; 2100 ppm would be representative of a non-emission controlled engine.

The high temperatures were effecting the NOx part of the emission control system in some way, but without a detailed understanding off all the emission control hardware and control systems it would be tough to sort out. Catalysts of that era were oxidizing only. NOx was controlled either with EGR, excess designed in valve overlap, or the spark timing map or a combination up to all three on on big, heavy cars. Excess valve overlap creates a full time EGR system, and GM used this strategy in the seventies, but it really killed low end torque and in town fuel economy.

Duke

After reviewing the emission controls for that model what you suggest makes a bit more sense. The puzzling part to the equation is the controls of that era are usually regulated through vacuum temperature switches. After a certain temperature is reached the valves are usually open, or closed depending on the circuit. Is it possible that vacuum valves of that era were designed to open at one temperature yet close at another temp? I discovered too much gray information regarding the actual operation of some/all the components in the emission control system for that era.

Thanks Duke.
:cool:

Several comments:

We may be saying the same thing with different words about fuel grades. Agreed that flame fronts and detonation are not the same. High compression engines require high octane fuel which burns slower, or lets the flame front complete its business, or whatever you want to call it. Lower octane fuel could result in quenching or detonation which can cause higher combustion temp and oxides of nitrogen or nitrogen dioxide. There really is no NOX. The x stands for an unknown just as in algebra. Cars requiring low octane do not benifit from premium, and in fact may suffer reduced performance.

Engine temps matter. All California testing station are required to have a huge fan to blow air at the engine compartment during the test to simulate road conditions. Stations are not allowed to pick their own fan. Only a state approved fan can be used. These fans cannot be used at the whim of the operator. There is an ambient temp sensor built into the testing machine that tells the operator when the fan must be on. The fan could be required to keep cars from overheating during the test, but I don't think that is the purpose. I've been told the purpose was to keep temps and nox down by simulating air flow during driving. I have seen no documention to that effect.

I was an electronics technician for 10 years before I become a Mercedes mechanic. I went through one solid year of electronics school five days a week. I was taught everything there was to know about electrons, outer rings, and co valent bonds and such. My point is that in those 10 years I ran into many situations where I said," well, so much for theory".

Peter

James.
Thanks for posting that info about the radiator. I had a heck of a time about a month ago getting a couple of my cars to pass nox. They are an 88 and 90 300SEL. I just boughy an 87 300E that smokes big time. The PO told me that it barely passed smog. After I correct the smoking problem, I'm going to do a little research on the cooling system. I have digital pyrometers, access to radiators at wholesale prices, and of course cheap labor. I just had a 560 SEC smogged this weekend. I checked it on my machine which is only a 4 gas analizer, and the readings were very low. I can't check nox, but it passed the smog with very low nox. I replaced the radiator about a year ago, because it was running hot. I know none of this is scientific, but it has got me thinking. Today I will go into my 1979 manuals and look at the system on your SL.

Peter

I have a some familiarity with GM's TCS (transmission controlled spark) used in the seventies era. TCS denies vacuum advance except in high gear on automatics and may have allowed vacuum advance in both third and fourth on four-speeds. Most configurations included a thermo-vauum switch that allowed vacuum advance at all times above 230F coolant temperature. When the engine cooled down the thermal vacuum switch cycled back to normal mode.

The vacuum source was usually "ported" i.e. the signal port was above the throttle blades at idle, so there was no vacuum advance at idle under any circumstances, but some configurations may have allowed vacuum advance even at idle when the coolant temp was over 230F.

Vacuum advance increases thermal efficiency at idle and low load by increasing peak flame front temperature, but with no vacuum advance the timing is retarded below "optium" so flame front temperatue goes down (less NOx) and EGT goes up. Essentially more of the fuel's energy is thrown out the exhaust rather than creating useful work on the crankshaft.

The only way to understand all these "add-on" systems on vintage cars is to get all the OE service documentation and study it thoroughly. All of the control functions that these "add-on" systems performed back then are integrated into the engine control electronics on modern cars.

Autozen - I've never had a emission test station place a fan in front of my cars for ASM testing, but since the test is relatively short the car fans keep the temperature in bounds though they do get hotter than normal. In the case of my 190 I want it as hot as possible to keep the converter hot. This is an issue getting M103 engines to pass.

I've checked the converter inlet pipe temperature with an IR gun after normal driving followed by extended idling. It starts at about 500-600F and drops to as low 300 after five to ten minute of idling, which is why these cars tend to have high emissions unless you manage the test properly to keep the converter as hot as possible i.e. go to a drive through test station with no line, and keep the engine at 2000-2500 until the tech is ready to drive it into the bay.

Duke

if you still can't figure it out, check on mr2oc.com. There are people on that board that know more about the car than Toyota.

My experience with that board (I own a '91 MR2) is that 99 percent of the participants are clueless when it comes to automotive engineering issues - VERY different than this board. The one good guy is billwot, who is an engineer and considerably older and more experienced with things automotive than most of the participants.

I gave up on the MR2 board over a year ago.

Duke

I got to my library today only to find that I have every new car intro manual for mercedes up to 93 except I don't have a 79. Not to worry I went to my service microfiche and pulled the one covering all the M117 engine emission systems from 72 to 80. The air pump always runs after it is picked up by a 17*C thermovalve.

EGR is activated through a 40*C thermovalve. EGR is activated during acceleration, during partial load, and during transition to decel. All this is done through a vacuum amplifier and is never shut off at higher temps.

I still think the idea of restricted coolant flow has some merit in high NOX readings. Remember theory is called theory, because it is just that. The reason that science progresses so slowly is because it always must follow scientific procedure. Tell that to Leonardo da Vinci

Peter.

The ancient Greeks thought the Sun revolved around the earth. We didn't figure out the truth until 500 years ago, and it hasn't been that long since science though the sun's heat came from burning coal.

Even early in the 20th century science thought the universe was only as big as our own Milky Way until Hubble proved that those smudges of light were actually other galaxies BILLIONS of light-years away rather than just clouds of gas in our own galaxy.

Sometimes we don't understand how things work because we don't have enough information, and sometimes we just misinterpret what we observe.

Duke

Duke, your experience on mr2oc was with the mark 2 crowd as you have a 91. I know nothing about that group. Mine is with the mark 1 crowd. The mk1 guys know what they are talking about. I have gotten very sound technical advice on that board. The original poster is asking about a mk1.

Gentlemen, this turned out to be a good post after all.
Autozen has answered a question I had and that it became obvious after the retest. The tech didn't have the fan in front of the engine running the first time, he had it running the second time.
The car had new sparks, premium gas and it reduced the NOx number by 300. I work at a major oil refinery and can atest that theory is just what is written but the practical application and experience changes evberything.

I'll go back to my 300E.:eek:

You see. There we go with science again. As an example: the medical profession which is based on science, believed for decades that ulcers were caused by stress and worry. It took an Australian medical doctor to inject himself with a bacteria to prove the whole SCIENTIFIC medical profession wrong. We now know that a bacteria called H Pylorie is the root cause of stomach ulcers. Science is so restricted by its codes and rules that it advances at a snails pace, not to mention the egos involved.

Peter

That's a good example. Medicine is primarily an empirical science, and the profession believed for so long that ulcers were caused by stomach acid caused by stress - whatever- that they REFUSED to believe that ulcers could be caused by bacteria even when confronted by evidence derived through rigorous experimentation. That said your conclusion that coolant temperature has a major effect on NOx is not based on rigorous experimentation.

Physics, chemistry, and engineering are sciences. I'm not so sure about medicine.

Considering that this revelation about the cause of ulcers only happened only about 20 years ago, I wonder how far we have come in medicine since the middle ages, and most advances in medicine - like artificial organ, limbs, and arthroscopic surgery are due primarily to the efforts or engineers, not physicians.

Duke

Agreed that engineering is a science which may explain why the Mulholland Dam failed and killed hundreds of people, and he was so distraught that he commited suicide. How about the scientifically built bridge in the Pacific North West that just went away. So much for science. You are trying to throw crap in the game by talking about the middle ages. As a matter of fact the middle ages occured after the crusades. The crusaders went to the holy land to teach those arabs a thing or two. What in fact really happened was that they brought back new medicines and new diets that were very beneficial to Europe.

In my opinion, if Einstein believed in scientific protocol. we'd still be using smokeless powder invented in 1894. Whether that is good or bad has nothing to do with the point.

Peter

Timing Question on Another Failure
 

My 1985 380 Having failed at 3.6g/mi with a limit of 3.0 NOX I am trying to adjust timing these are my initial readings.

2 deg retarded at idle without vac adv cold
7 deg advanced with vac cold
I took these to check the temp advance

when hot
10 deg adv at idle w/vac spec range is 13-19 deg
30 deg adv w vac at 3k rpm spec range is not specified

25 deg adv without vac at 3k rpm spec is 25 deg at 3k

My question is that I had it in the shop and they were to retard the timing to make it pass the test. The idle readings are retarded but the high speed settings are not.

I realize there is centrifical advance taking place should I set it back to 20 deg advance at 3000 rpm without vacumn?

Is there a reason why the idle settings are retarded below spec range and the higher rpm are not?

Thanks for any help provided I realize I am new here, learning a lot and the ropes in where to post things.

Bob,

Welcome aboard. You scored alot of points by posting the year and model in question. It gets real irritating when someone asks a question about something like timing on their car. Stevebfl always fires back the question. Is this a Ford or Chevy? That being said. How does your state run the smog check? Is this on a dyno and what speeds? I also notice you mentioned grams/ mile while Ca. measures parts/ million. I don't have any of my reference material here now. I will have to bring it home to help answer your questions unless someone beats me to it.

PS What are the rest of the readings?

Peter

Assuming your engine has a conventional centrifugal advance mechanism, +/- 2 degrees is their typical tolerance range, so retarding the initial timing 2 degrees may not make much difference at higher engine speed.

Suggest you retard the initial timing about 6 degrees from spec. The initial timing spec is on the "tuneup/emission lablel", which should be located somewhere in the engine compartment.

The other way to reduce the timing at part load is to disconnect the vacuum advance, assuming that vacuum advance is active during the test, which is may or may not be depending on the details of the emission control system and test conditions.

Duke

Thank You
 

Thanks to Peter and Duke for your help.

Peter,
The Mass test is a dyno the NOX was the highest at the steep acceleration ramp I would assume it was full throttle and therefore full advance. The other readings were:

HC limit 2.00 actual 1.16
CO limit 30 actual 6.47
CO2 limit none reading 379 all grams per mile
and NOX limit 3.0 actual 3.6 last time


Duke
The emission label is missing I was going by the MB CD for engine group 116.962 gives the advance settings for the distributor that I quoted earlier because the test failure was at full throttle then should I retard the 6 deg from the 25 deg advance without vacumn and make it 20 probably as close as I can come at 3000 rpm. The 25 deg setting looks right as the balancer has a welded in post at 25 deg mark.

Another strange thing is that I cannot find an EGR valve on this car I have the MB SL CD and find reference to it but nothing under the hood as far as lines or valves on the exhaust manifolds. All other emissions equip seems to be in place and working the air pump etc. Was it removed or were there engines without it?

I also changed plugs they were a bit carboned up and a new air filter.
Thanks again.

Re: Thank You
 

I would think the CD would have the spec for initial timing, but if it's not available reducing the 3000 RPM timing spec six degrees (vacuum advance not connected) would be the same as reducing the initial timing a like amount.

I'm not aware of any emission test procedures that require WOT. Even the federal/CA certification test comes nowhere near WOT on a reasonably powered car. The proper emission/tuneup label has abbreviations for all the emission control systems, so it will tell you if your engine originally had EGR. You can probably buy the correct label for you car through Mercedes parts. In not abolutely sure, but in CA lack of an emission control label may be cause for failure.

Prior to your next test you could also plug the vacuum advance line temporarily and unplug it after the test. Plug the line internally and reconnect it, so it won't be visible on the visual inspection. The car will run poorly and maybe hot, but the lack of vacuum advance should reduce the measured emissions. You don't have that far to go.

Duke

Bob,

Got a chance to go through my 84 and 85 model year books and those cars were not equipped with EGR. You should have an air pump, but that doesn't do much for NOX. Actually your overall readings look very good, and you wre close on NOX, but we all know that close only counts in horseshoes and hand grenades. It looks like you have some room to tweak up CO a little which will probably reduce HC and maybe NOX. I wouldn't mess with timing except maybe retard it slightly. Your state probably has visual specs on timing that must be met. One thing that has worked well here in Ca. to reduce NOX is to hook the car up to one of those carbon blaster machines. It's like a dialysis machine for cars. You hook the machine up to the car fuel system, draw out a gallon of fuel, add a special additive to the gallon, disable the fuel pump, and run the car at idle for 45 minutes on the machine. If you know what you are doing, there is a less sophisticated way. You can run the car on water injection to clean out the carbon.

Peter

Don't know about other states, but CA allows a maximum of 3 degrees advance from the initial timing spec and unlimited retard.

Retarding the timing is a quick and easy way to reduce NOx due to lower peak flame front temperature. It will also reduce HC and CO (as long as there is available O2 in the exhaust) due to higher EGT that will increase converter temperature.

Duke