Hello

I just failed the California Smog emissions test with my 1987 300E

HC and NO were high

see results below


any ideas on where to start, I just changed the plugs, wires, cap and rotor and an oil change before the test

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in order of importance , make sure no vacuum leaks, check if egr working, replace o2 sensor if more than 60k miles old, too much carbon buildup ie high compresson for no too high , catalytic converter , compare the last few years of smog checks , I found out they lowered the limits , meaning your car has to run cleaner than new,

thanks for the reply.

Just before the test I replaced the two air idle hoses from the idle valve. Also replaced the hose off the top of the air cleaner housing and the breather hose off the head. Also changed many of the small rubber hose fittings / elbows. I has a slight vacuum leak at the intake manifold and tightened it up and got much better results.

The vehicle does not have an EGR system so it relies heavily on the CAT to reduce NO.

I believe the O2 sensor is 33 plus years old the vehicle has 233 k miles

I have noticed over the years that they have lowered the limits however from 2 years ago to todays test they are the same.

What does a CO2 of 13.3 and 14.3 tell me?

What does a O2 of 1.6 and 1.0 tell me?

attached is the test from two years ago.

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Quick way to pass, since your O2 sensor is 33 + years old replace that, then go get yourself a new cat. You should be able to get one for a few hundred dollars. They're relatively inexpensive.

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1990 190E 3.0L

It's been awhile since a CA emission test failure has been reported on a M103 engine, which surprises me. You're registration renewal probably directed you to a "test only" station and either the renewal form or the test report says "high emitter profile."

If the emission system is performing optimally the O2 content should be zero or no more than 0.1 percent, and CO2 should be over 15 percent because all the O2 has been consumed oxidizing HC to H2O and CO2. O2 content is a key piece of diagnostic data. There is a little bit of O2 in the exhaust gas. Plus the converter creates O2 by disassociating NOx to O2 and N2. So if there is no O2 at the tail pipe, the three-way catalyst is working at peak efficiency.

Catalysts "age" with miles and need to be hotter over time to achieve peak efficiency. Also, getting over 200K miles from an O2 sensor is a lot, but they don't last forever. If your 300E was originally sold in CA it should have diagnostics that are not on 49-state models and the "check engine" light should illuminate with a code for an O2 sensor fault, but maybe not in all cases. I believe Mercedes called for replacing the O2 sensor every 60K miles. My '88 190E 2.6 still has the original, but it only has 85K miles.

About ten years ago I did extensive testing on my car due to high HC readings. It passed, but had little HC margin, especially the 15 MPH test. I found information on this site about the R16/1 resistor. It controls the rate of spark advance with engine revs. The OE resistor is 750K. Removing it increases the rate of advance with revs and replacing it with a shorting plug (made out of a short piece of wire with the insulation removed from the ends, formed into a "U" and jammed in the socket) decreases the rate of spark advance with revs.

For normal driving my R16/1 resistor is not installed and for emission testing I install the shorting wire and replace the short molded rubber hose from the inlet manifold nipple to the 3mm nylon tube that goes to the EZL module with a piece of generic 1/8" vacuum tubing that is plugged with silicone. This disables the vacuum advance.

For a given speed and load the less ignition advance, the lower the peak combustion temperature, which lowers "engine out" NOx. At the same time it increases EGT, which will increase catalyst bed temperature

This configuration lowered my HC by about 50 percent and NOx a whopping 90 percent, though NOx was not a problem, and O2 is 0.0% at both speeds, so the catalyst is operating at peak efficiency. The engine is totally doggy below 2000 due to the retarded spark advance, but both tests are below 2000 (2nd and 3rd gear) so the effect is dramatic. I use a "drive though" test station a couple of miles away, but use a 5-mile route to get there so the cat fully warms up. I usually arrive about 0930 and get right into a test bay or maybe wait for one car to be completed, and NEVER SHUT OFF THE ENGINE. In fact I open the windows, turn on the A/C full and keep engine revs at about 1200-1500. This helps keep the catalyst hot.

Assuming you have a free retest you can replace the R16/1 resistor with a shorting plug and plug the vacuum advance as I described above. This will help, but may not be enough to do the job with your aged O2 sensor and catalyst, but it costs nothing out of pocket.

If it still fails I would probably replace the O2 sensor first and then the cat if it still fails, but let's wait and see what the new results are.

I strongly suggest that you search for threads stated by me, Duke2.6, using search words R16/1 resistor, and read those threads to understand how spark timing affects emissions and how to modify the spark advance map by shorting the R16/1 resistor disabling vacuum advance. As you probably know the initial timing is not adjustable - mine is 9 deg. BTDC, but that's okay. Retarding the rate of advance with engine revs and disabling the vacuum advance is more effective and easy to do on these engines.

Back before I learned about the R16/1 resistor, fifth gear was not useable below about 45 MPH - no torque. With it removed I can drop it into fifth at 35 MPH, and it easily pulls from about 1200. Around town fuel economy also improved by nearly 20 percent! The difference may not be as dramatic on an automatic (that I assume your car has), but is probably noticeable.

The R16/1 in my 190 is located on the plastic cover inboard of battery. It's visible and looks like a unconnected electrical connector wrapped up in electrical tape, so it's easy to access, but I remove the battery which takes about a minute to get better working space.

I believe it's in a different location on the W124 chassis - somewhere near the master cylinder, although that might be for the S-class, I'm not sure. More searching on the R16/1 resistor should lead to the location because there was a lot of discussion on this ten or more years ago, but not recently.

BTW, I'm a retired automotive/aerospace engineer - MSME from the U. of Wisconsin Engine Research Center where I did emissions research, so I understand emission creation and control at a very low level of detail.

Keep us posted.

Duke

Interesting info about the resistor. I ran my car with the resistor and monitored more than a dozen fill ups and also did the same thing without the resistor using only 91 octane. Lowest combined city/highway driving with resistor was 15.7 mpg and the highest was 22.3 mpg. Without the restor my lowest was 17.2 mpg and my highest was 24.5 mpg.

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1990 190E 3.0L

Most of my driving is now pretty local - surface streets with round trips of 5-10 miles... almost no freeway driving. I think the reason I got a better improvement in fuel economy is that I can now use fifth gear on typical 35 MPH boulevards.

I don't have to downshift until below about 30 MPH, which is about 1100 revs. Below this I can feel the engine labor and response is sluggish - probably due to lack of sufficient spark advance. Given the torque peak of 4600, the engine is not designed for low rev torque, but it has excellent torque bandwidth with the R16/1 resistor removed from 1500 to the rev limiter.

My engine system engineering requirement for a responsive high performance road engine is 80 percent peak torque at 2000 with a manual trans and 90 percent with an automatic. Back in the nineties I had my car on a chassis dyno, and it actually made 80 percent at 2000, which surprised me because it felt pretty soggy down low. With the R16/1 removed it must make 90 percent at 2000, which is excellent for such a high torque peak engine!

I actually just use 87 PON, and if ambient is below 70 and coolant at the usual 80C it doesn't detonate, even if I drag it down to about 700 in second gear at a stop sign and then go without declutching and going to first. Since I usually only drive it during the cooler months, 87 is okay, and if ambient is over 70 and coolant is over 80C I can "drive around" any slight transient detonation by shifting at higher revs. Usually I shift at 2000-2500.

You've got a 300E, right? Where's the R16/1 resistor located?

Duke

Fantastic info above and beyond the basic "if the HC is too high the engine is running rich, if the NOx is high you need to bring down combustion temps with more fuel or by fixing the EGR" tips.

Saved for future reference.

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HI

I was out of town for a while.

Just went through my smog test results going back to 2004 and made a spreadsheet of the results.

There were times in the past that the HC was high but just passes.

It seems like with the latest test all measurements are on the higher side , even the ones that passed. I am going to take some voltage measurements of my O2 sensor with a voltmeter to see how it is functioning.

let me know if you have any comments to my results over the years.

Thanks

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When I go through the smog I drive there in first gear to get the cat lava hot and then leave the car running. Seems to work.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

then move out of the commie state,I did in 83

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

I don't see any clear trends over the years. The 2004 test was very good, but then some emissions went up and back down again. This is typical and is probably due to differing test conditions and equipment calibration. Then there was a dramatic increase in emissions from the 2017 test. The high CO and HC indicates a rich mixture, which could be caused by a degraded O2 sensor, or it could just be insufficient catalyst temperature. As catalysts "age" ever higher bed temperature is required to reach peak oxidation and reduction efficiency.

The cat heats up during the 15 MPH test, which loads the engine more than the 25 MPH test, so emissions are usually lower for the 25 MPH test.

You should check O2 sensor function. What's total mileage on the car? It may just be wearing out, but I'd make an even odds bet that if you short the R16/1 resistor socket and plug the vacuum line to the EZL module to disable vacuum advance it will pass. This cut my HC by about 50 percent and cut NOx by a whopping 90 percent!

The reason is that the retarded spark advance reduces flame front temperature below the "knee" where NOx formation dramatically increases. I'm not sure exactly where it is, but a few hundred less than 4500F. The retarded advance also increases EGT, which gets the catalyst hotter, so it more efficiently oxides HC and CO2 and reduces NOx. Again, the key is O2 content. It it's zero or no more than 0.1 percent, the cat is operating at or near peak efficiency, and the "E-part" of the KE system, which includes the O2 sensor is maintaining the ideal stoichiometric mixture.

The emission test station I go to ("test only" type required) is a "drive through", like a car wash, with three bays about two miles from my house, but I take a five mile route to get there to fully warm up the engine and accelerate aggressively - put as much load on the engine as possible to heat up the cat.

I test in February, and arrive about 0930 and usually go right in or am the first in line. I open all the windows, turn the A/C to max and hold revs at about 1500 while waiting, again to keep the cat hot. The more load on the engine the hotter the cat gets.

Never leave the car at a test place and pick it up later. Always go to a place that gets you in quickly and NEVER shut off the engine.

BTW before the end of the 25 MPH test the aux. electric fans switch on which means coolant temperature has reached 105C. Since I usually only drive it during the winter months, they never come on, except during the emission test due to the "special" spark advance map for emission testing. In fact I can't even remember the last time the coolant temp hit 100C, which is the point that the viscous fan clutch tightens, and I hear it "roar" above about 2000 revs.

Duke

Same here but moved back because I like to go snowboarding and hang out on a sunny beach in the same weekend.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Do some research on LA smog in the 60's and get back to us if you still want to live there without emission controls.