89 260E Fails CA Smog Test
 

I'd appreciate thoughts from the group on my test results:

Test 1: Friday Aug 12 (Failed due to faulty Check Engline Light)

MPH=15 RPM=1546 %CO2=14.9 %O2=0.1 HC(PPM)=43 CO(%)=.13 NOx(PPM) =762 Pass
MPH=25 RPM=1864 %CO2=14.9 %O2=0.1 HC(PPM)=21 CO(%)=.07 NOx(PPM)=648 Pass


Test 2: Monday Aug 15 (Fixed Check Engine Light)

MPH=15 RPM=1517 %CO2=15.6 %O2=0.0 HC(PPM)=41 CO(%)=.15 NOx(PPM) =948 FAIL
MPH=25 RPM=1714 %CO2=15.5 %O2=0.0 HC(PPM)=14 CO(%)=.06 NOx(PPM)=662 Pass

Any thoughts on where I should begin to source the problem. New 02 sensor and Bosch plugs were installed 3-weeks ago.

HC and CO are very good for a M103. Zero O2 means the catalyst was working at high efficiency. The high NOx may mean an EGR problem. You need to do a thorough functional check of the EGR system. Even if it is not working, judicious diddling to the ignition map should lower NOx. My car was low double digit NOx, and it doesn't even have EGR.

Read the following thread and the threads it links to:

http://www.peachparts.com/shopforum/tech-help/117048-successful-ca-asm-emission-test-ke-fuel-system.html#post833484

I hope the "Bosch plugs" are H9DC. That is the ONLY Bosch plug that is correct.

One question: What was the cause of your "faulty" check engine light? Did it yield an EGR code?

Duke

Does the M103 even have an EGR in that configuration? Mine doesn't. NOx is produced when the combustion temperature is high. You might just pass if you short the aux fan switch for constant operation.

"One question: What was the cause of your "faulty" check engine light? Did it yield an EGR code?"

Duke, the Check Engine Light has was simply bad. I replaced the bulb, and the engine light stayed on. I disconnected the battery for a minute, then reconnected, and the Check Engine Light operated normally.

"NOx is produced when the combustion temperature is high. You might just pass if you short the aux fan switch for constant operation."

Moneypit SEL, are you suggesting that I short the aux fan so it is always on? I have noticed for some time that the engine operates at high temperatures. I believe I have a leak or something else that has caused a pressure loss in the cooling system and have not had time to diagnose it. Do you think this high temp operating condition could cause the higher NOx?

Double check all fan operations, contrary to some schools of thought the reality is engine temperature does indeed affect NoX. I have been involved in a number of mid 80’s MB vehicles that did not meet the CA emission standard due to high NoX. Speaking from personal experience get your engine temperature stabilized to around 80C and you should fly through the test. All your other numbers look great

My knowledge is that M103 engines were not fitted with EGR valves until 1990, at least out here in the land of fruits and nuts. :D

Yup. Heat causes NOx. Running the fan for the test may well allow you to pass. Shutting the engine off and allowing it to cool down may also work. There's nothing else in your test numbers to indicate any other type of problem.

What do you mean by 'engine operates at high temperatures'? Do you just think it too high, or did it used to run cooler? What temperature is it running at now? If it engine used to run cooler than it does now, fixing that will fix the NOx.

Please read my referenced threads, which explain how NOx is created. It is created in the flame front at 4500 degrees F and has nothing to do with engine coolant temperature.

Retarding timing reduces peak combustion temperature and significantly reduces NOx even though it increases coolant temperature due to the higher EGT transfering heat to the cooling system as the exhaust gas traverses the exhaust port. How do you think my car's NOx measured low double digits?
Also, high EGT keeps the converter hotter.

Some people here need to read the emissions information I posted and reference on this forum to learn what's going on and quit posting myths, misinformation, and amateur theories!

I did graduate research in IC engine emissions generation and control at the U. of Wisconsin Engine Reserach Center, and I understand the subject at a low level of detail.

If anyone has better credentials than this, I, and I'm sure others, would like to hear what they are.



Duke

Are you seriously trying to say that an engine running too hot won't produce higher NOx readings? I've seen it happen with my own lil' eyes.

TEST 3 (FAILED BADLY)

MPH=15 RPM=1537 %CO2=14.6 %O2=0.4 HC(PPM)=143 CO(%)=.32 NOx(PPM) =1749 FAIL
MPH=25 RPM=1536 %CO2=15.0 %O2=0.1 HC(PPM)=46 CO(%)=.13 NOx(PPM)=706 Pass

The car was running at approximately 90C during the test - I added coolant to the system, as it was low during the previous day's test. Any idea why my numbers are going south?

In general, the used to run at approx 80C, but then I sprung a leak in the cooling system and now it usually runs at 100-105C.

Duke, no one discredits your credentials. All the science in the world, all the math in the world and all the degrees obtainable will not explain why theory and reality simply do not align at times. Point in case, what is your theory on electron flow? Has anyone been able to prove or disprove either of the two most popular theories? From time to time experience can and will contradict theory, it is the education process. My numerous experiences need to respectfully disagree with your educated conclusion that “high engine temperature” has little to do with elevated NoX readings. :cool:

I have resolved 15 to 20 cases of high NoX on MB vehicles, the vehicles were tested extensively and we found little if any of the traditional contributing factor as a cause. The majority of the vehicles I was involved with were not fitted with EGR systems (1981 to 1985 380’s and 500’s) with the exception of the following vehicle. I worked on a 450SL that did have an EGR system and it was fully functional according to all MB literature, however the NoX was hovering around 2000. After 15 plus hours devoted to all theories regarding NoX production and ensuring that all systems were operating according to the manufacturer specifications, we needed to shift our attention. That particular vehicle was running around 100c so we installed a new thermostat and rodded out the radiator. After this repair was performed the NoX dropped below 500. Theory vs. experience, theory did not win in that experience. :rolleyes:

We can both have our opinions and both opinions can be respected right? Just like electrons flowing from negative to positive,………………when I see the electrons with my two eyes moving from negative to positive than I will believe the theory! :D

Are there any DTC's in your system currently? If so you will need to address them. Also, is your fuel injection system adjusted to MB specification? Is the ignition timing correct? Is the vacuum line connected to the EZL control unit? What about your engine temperature? Are you able to get it below 90c? Lowering the engine temperautre will help once all the other factors have at least been double checked.

IMHO: H9DCO (good choice), fuel control set between 40% and 50%, and +/- <10% differential idle vs. high speed (2500rpm)

Always :cool:

MrCjames , please excuse my ignorance, but what is a DTC?

DTC = Diagnostic Trouble Code
A fault in any system that the engine computer monitors will set a DTC, which will help identify the problem.

Personally, I think that if you get your engine cooling system back in the 85—90C range, you'll have no trouble passing the emissions test.

Hi steven, I am sorry I was unable to get back to you last evening.

Thanks moneypit! :sun_smile

I try to incorporate the the defintion of acronyms whenver I use them in my responses, I'll work a little harder at in the future. :o

Always :cool: