1987 300E just failed California Emissions Smog Test - PeachParts Mercedes-Benz Forum

murphysf · #1 08-20-2019, 12:25 AM

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

speednjay · #2 08-20-2019, 02:05 AM

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.

Duke2.6 · #3 08-20-2019, 11:28 AM

Quote:

Originally Posted by murphysf

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

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

murphysf · #4 08-21-2019, 12:54 AM

Quote:

Originally Posted by Duke2.6

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

Thanks

I'll consider jumping the resistor and plugging the vac line.

I was away out of town for a while.

I just measured the O2 sensor voltage. Started the car it was already warmed up. Voltage measured around 440mV, let it run for a while and reved it a bit and it reading on the digital meter jumped around between 100mV and 700mV

According to what I have read this is the typical behavior.

I was surprised that it jumped around that much at idle and also when I would hold to rpm up around 2k rpm.

I also confirmed that 13.5VDC was going to the heater part of the O2 sensor.

I guess my O2 sensor is fine?

murphysf · #5 08-21-2019, 01:20 AM

Quote:

Originally Posted by Duke2.6

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

so to confirm short R16/1 which will yield 12 degrees of retard. I read lots of posts about people removing the resistor and leaving it open which is no retard.