For the low speed test HC standard is 220, my 300E had a reading of 390 which made it fail. It passed the high speed test. Any idea what could be the cause of the high HC reading?

Thanks in advance.

Probably the cat wasn't hot.

Otherwise the answer is that the car isn't in closed loop or the cat is dead.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks for the response. I drove the car for about 45 minutes before the test, so I think the cat should have been hot enough. The engine computer should be in closed loop mode now as that was one of the first things that was supposedly fixed when I bought the car. So it sounds like the cat. Should I replace just the main cat or should I do the "pre-cats" as well?

Thanks again.

Normally, when I see high HC at idle, I focus on ignition misfires or oil consumption problems.
When was the last time the engine had a good tune-up ?

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2007 C 230 Sport.

Low speed HC seems to be a problem with the 103 engines. I'm marginal in my latest CA "acceleration simulation mode test" scoring 113 ppm against a limit of 116 at 15 MPH, and it didn't help that they lowered the limit from 141 in the previous test a little over two years ago. The 25 MPH HC is much lower relative to the standard.

Converter temperature appears to be an issue, so driving the car to thoroughly warm it up and not shutting it down prior to the test is important.

Do you know the history of your O2 sensor? I have a suspicion that they can "drift" without giving a check engine light. My current plan in two years is to have my '88 190E 2.6 tested, and if it fails, just throw a new O2 sensor in it and see if that helps. The converter system is very expensive, so you want to exhaust all other possible causes before replacing the converters.

You should also search the board under "emissions","O2 sensor" and "duty cycle" as you will learn how to test the behavior of your O2 sensor, and I would recommend just replacing the O2 sensor apriori if the duty cycle is out of spec before you attempt adjusting the air flow meter as an O2 sensor that has drifted out of calibration will affect the duty cycle while not sending a properly calibrated signal, which could cause a rich or lean condition.

Your limits are higher than in CA, and I assumne your state uses a different test. What state are you in and what is the test procedure? I/M 240?

I'd also like you to post your complete test results - HC, CO, NOx, O2, and COx and the standards/averages for each test if all of this data is available on your test report as it is in CA. Looking at the entire results can help diagnosis. For example, high HC and low CO can indicate excessive misfires, which points to the direction of ignition system commponents such as the cap, rotor, plugs, or wires.

Duke

All of these tests are much less stringent than the original standard the car is built to. When I am testing these cars with an exhaust gas analyser I only believe my readings for about a minute at the most. A car with a good cat will read 0.0 CO as soon as the cat is hot BTW it some how doesn't seem strange to me that a 15 year old cat wouldn't work as good as new.

We brought a few cars in from Germany (grey market stuff) in the early 80's. We had to bring the car up to the standards of the federal test sequence; much harder than ASM or IM240. We had to haul the cars to a test lab in Ft lauderdale. The test lab was in an industrial jone and the tests were so tight that back ground readings were taken to justify the actual readings. We had one 500SEL so clean that on the warm bag we cleaned up the hydrocarbons from the background. In other words the air coming out the exhaust was cleaner (for unburned hydrocarbons) than the air we were breathing.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The O2 sensor was replaced last August. Here are all the results from the test:

High speed @ 2574RPM
Standard Current reading result

HC 220 137 pass
CO 1.2 .50 pass
CO2 14.5 n/a


Low speed @668RPM

Standard Current reading result

HC 220 390 fail
CO 1.2 .64 pass
CO2 14.3 n/a


Anyhow, the engine is running good. The plugs cap and wires are all good, air filter new. Uses about a quart of oil every 3000 miles. I'm inclined to believe what Steve said which was that I need a new cat. Should I go for new pre-cats and center cat as well when I do the change?

Thanks.

Okay, I take it your test was the "two speed no load" test at idle and 2500 RPM.

Does your test report show the amount of O2 in the exhaust? That can add to the story. Your CO2 looks a little low so I would expect to see a few tenths percent 02 if it was measured and written on your test report. Less than 15 percent C02 with a few tenths percent O2 in the exhaust could indicate less than complete combustion and possibly point to the coverters.

I'd like to pursue these M103 emission issues further, and they may apply to all KE system Mercedes engines from the eighties era. The following are test results from my latest California Acceleration Simulatin Mode (ASM) test. This test is done under load on a chassis dynamometer at 15 and 25 MPH, and the load is more than required to maintain a steady speed on a level road, so it simulates acceleration at constant engine speed. My car is a '88 190E 2.6 with a manual transmission, 75K miles. The test is done in second gear for both speeds on this model to maintain the acceptable RPM range. Also, for the last two tests I have been directed to a "test only" station - probably because this engine family has been identified as a high emitter, which is one of the criteria for requiring a test only facility.

Read the data as :

test result/pass limit/average for year group

15 MPH / 1657 RPM

HC: 113/116/31 ppm
CO: 0.36/0.74/0.10 %
NOx: 261/791/237 ppm
O2: 0.1%
CO2: 15.3%

25 MPH / 2665 RPM

HC: 58/91/20 ppm
CO: 0.18/0.62/0.09 %
NOx: 188/199/730
02 0.0%
CO2: 15.3%

The first thing that pops out is the low O2 level. My engine does not have EGR or supplememtal air injection. I believe EGR was added in '89. Does anyone know of any 103 engines with air pumps?

O2 is required to oxidize HC and CO, and on my engine the only sources of O2 are the native exhaust and any reduction of NOx in the three way converter. Once all the O2 is consumed the converter can't do anymore, which is why I think my O2 sensor may have drifted - that is, it is reading less O2 in the exhaust than actually exists, which is causing the system to run slightly rich. The 15+ percent CO2 is an indication of complete combustion.

The '88 maintenance schedule calls for replacement of the O2 sensor once at 60K miles, but I did not do this task. Being as how my CA version has some limited OBD including O2 health and I have never had a check engine light, I decided not to change it, but the OBD is probably not capable of detecting all O2 faults.

The 25 MPH test shows lower HC and CO relative to the standards and year group average and could indicate greater converter efficiency as this test is done immediatly following the 25 MPH test, but the 25 MPH test has a lower relative load. My impression from inspecting other test reports on a wide variety of cars is than the 15 MPH HC is usually the acid test.

I can't draw much in the way of conclusions from the NOx data. Both the test results, limits, and averages have varied widely over the ASM tests that have been done on this and my other cars. It appears that the Califronia Bureau of Automotive Repair is still fiddling with the sampling and software.

The first two emission tests, which were the old two speed no load test showed very low emissions, but they jumped in '95 at 54K miles, so something happened between the '93 and '95.

For those of you who have some expertise in emissions and test analysis, I'd like to hear your remarks.

Duke

Hi there,
I think it's just running a little rich. Notice that the high speed HC is also way high, although it did pass. Normally you would expect to see the high speed HC under 50 or so, and the idle HC under 75. There are several things you could do, one being raising the idle speed a bit, which might help things. You might look at the gasoline mixture - maybe it doesn't have enough wood alcohol in it - HINT, HINT My car doesn't even have a catalytic converter on it, and the HC tests at under 75 even at idle, without any "help". You might also verify that the ignition timing is correct at idle, and possibly retard it a degree or two. You have too many unburned hydrocarbons in the tailpipe. As has previously been stated, this is many times a misfiring plug - make sure the plugs are correctly gapped - too close a gap will cause misfiring at idle.
If you have access to a 5 gas analyzer it is very easy to play with things and see what helps or hinders.

Good luck with it!

Richard Wooldridge
'82 300D/4.3L V6

From a just getting the car to pass point of view, I had the same problem. Fine on everything but HC.

I changed the oil, and it passed. My car eats about a quart and a half every 3000 miles, most of that consumed in the last 1000...

Regarding underlying issues of oil consumption, or other probable causes? I bow to the wisdom of people who actually know about cars.

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jeremy wood
'88 260E ~200,700 miles
- All stock, except for Blaupunkt "Miami Beach"

Yes. You need to change oil just before the test. The old thin oil will slip past the rings and valves and burn easier than new oil. If you burn oil, it will burn incompletely and give you HC.

So, change oil, and if you want to be sure, add a bottle of STP oil treatment to thicken up the oil a bit more.

Ken300D