For a 1989 420 SEL with 240,000 KM, my emission inspection shows :

At 40 KM/h (1384 rpm)
HC PPM 53
CO% .05
NO ppm 73
dilution 15.05

at curb idle (670 rpm)
HC ppm 43
CO% .00
dilution 12.00

I did have to fiddle with the mixture to get a pass. Do I need a new cat.? What would the readings be if I do need a new cat?

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1989 420 SEL

Given the low CO, I doubt it. HC on Merc engines of this era is typically higher than average for similar vintage cars (especially M103s), but I don't know why. Your numbers appear to be pretty good (especially NOx) for an '89 vintage car, Merc or otherwise!

O2 content in the exhaust is the key to understanding the operational efficiency of the catalyst(s). Does your test report list O2 content?

Also, what kind of test? It appears that the car was checked under load on a dyno at 40 KPH, and then an idle test was done(?). Can you explain the test procedure in more detail.

Does your test report state the limits for passing and average passing numbers for the year group?

I'd be a happy camper if my car had numbers this low on the CA ASM test. I've been at the ragged edge (113 HC limit at 15 MPH) for my last three or four tests.

Duke

No O2 listed in the test results. Yes, the 40kph test is on a dyno. The car has 241,000 KM.

Here are the limits for passing
40 km/h
HC ppm 58
CO % .32
NO ppm 0630

Curb idle
HC ppm 200
CO % 1
NO ppm not applicable

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1989 420 SEL

Duke2.6

I can answer some of these questions for you.
Our test consists of:
1. Pre-conditioning cycle ( running on the rollers for 2 minutes, to dry wet tires, warm up cat, etc. ).
2. Run vehicle at constant speed of 40 km/hr. at a very light load ( about 25 hp ), for a maximum of 90 seconds. If the numbers are way below the standard, the computer may halt the test sooner.
3. Stabilize idle speed & measure idle emissions.

Last test on my vehicle for instance:
2500 rpm CO limit: 0.70 % actual: 0.00 %
HC limit: 150 ppm actual: 6 ppm
NO ppm: N/A

Idle CO limit: 0.70 % actual: 0.04 %
HC limit: 150 ppm actual 6 ppm.

The limits are periodically adjusted ( usually donwward ), to reflect a history of actual readings of the same year,make, model of vehicle.

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2007 C 230 Sport.

Thanks for the rundown on the test, manny. Your car is obviously very clean, but that's what I'd expect for a late model car.

The '89 420 SEL is very low on CO and NOx, but high on HC, which is somewhat typical of KE equipped models from that era though the V-8s seem to be cleaner than the inlines sixes. I'm not sure why, but I have a couple of theories - excess quench area, which causes high engine out HC emissions or high cylinder to cylinder A/F ratio scatter relative to a typical electric solenoid injector equipped engine. Either or both could cause relatively high engine out HC and, and there may be not enough 02 available to oxidize them down to a low level. CO probaby has a higher oxidation affinity than some of the HC species so the available O2 oxidizes almost all the CO, but leaves a good deal of HC.

In CA we have no preconditioning unless it's raining and they do the "tire dry" procedure. Four years ago I went on a rainy day and specifically asked them to run the tire dry test as I knew it would heat up the converter. HC was 20 percent lower that the previous ASM test. Two years ago I went on a dry day and it barely squeaked by.

I'm developing a strategy for my upcoming test in the next sixty days.

Our standards are based on year group, not make and model and most KE equipped Mercs have been identified as "high emitter profile". Many fail marginally or just squeak under the limit.

Your idle limits are pretty generous, especially considering that the test is run immediately after the conditioning and light load 40 kph test.

Duke

The V8's tend to have lower HC because they have air running around from behind the Kjet fuel injector which helps with the mixing of the fuel and incoming air while the 4cylinder and 6 cylinder engines didn't.

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Alex.

MB Tech
Sydney, Australia
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