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#31
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If your CO mixture is set to factory specifications (40% to 50% using factory test device) and you discover the CO is still elevated than the Pre-cats might be the cause.
My personal preference for Mercedes vehicles is to always lean in the direction of a factory catalytic converter. Good, bad, or indifferent it simply is a personal choice. |
#32
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I don't work in automotive emissions now, but I did graduate research in the field at the University of Wisconsin Engine Research Center. Duke |
#33
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If the air pump operated all the time the exhaust consituency into the converter would not be correct for NOx reduction. That's why air pumps on modern cars usually only inject air during warmup. If the pump control system was modified to inject air all the time, it could reduce high CO or HC, but NOx could be a problem. If CO or HC is high the fundamental cause of the problem should be corrected rather than trying a band-aid solution. Duke |
#34
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Just during warmup, it's function is to assist with heating the catalytic converter. Much like building a fire, if you blow on the coals they get hotter due to the increase in oxygen.
Same concept. |
#35
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Duke,
There is a thermo-vacuum switch, which either opens or closes (can't remember right now) when the temp comes up. The vacuum line comes off that swicth to the right fenderwell(might be different for a 300E) where it attaches to the power switch for the AIR pump.
__________________
Mike Tangas '73 280SEL 4.5 (9/72)- RIP Only 8,173 units built from 5/71 thru 11/72 '02 CLK320 Cabriolet - wifey's mid-life crisis 2012 VW Jetta Sportwagon TDI...at least its a diesel Non illegitemae carborundum. |
#36
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So you're saying that the pump continues to pump air, but a switching valve diverts the air and dumps it overboard rather than injecting into the exhaust once the O2 sensor is hot enough to enable closed loop operation(?).
Duke |
#37
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#38
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Doers the O2 sensor fail gradually?
I passed the TX smog test but not by much. I will post the numbers if needed. My 87 300E has 320K miles and has not had the O2 sensor replaced in the last 200K miles at least. Can it be bad even if the car runs ok?
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#39
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I'd like to see your numbers, and the passing limits. (I'll give you a free analysis.) Also, what kind of test? List CO2 and 02 if available.
Most cars will run okay with a bad 02 sensor. On board diagnostics will pick up some failure modes, but not all. 02 sensors can get "lazy" with age and respond slowly, which can effect emissions. Modern OBDII systems might be able to pick this up, but not your vintage electronics. You can eavsdrop on the O2 sensor with a scope and make a subjective analysis of its behavior. Duke |
#40
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Here's another recent KE emission test data set from a '88 560SEL owned by a friend. Car is well maintained with 160K miles. O2 sensors, cap, rotor, spark plug wires and valve seals have been replaced, but no other major work has been done to the engine or fuel system and the converters are original.
15 MPH (1438 RPM) CO2 15.0% O2 0.0% HC 70/100/31ppm CO .06/.67/.10% NOx 39/741/237ppm 25 MPH (1452 RPM) CO2 15.0% O2 0.0% HC 42/74/20ppm CO .05/.54/.09% NOX 38/680/199ppm Note that O2 is zero so the converters are operating at 100 percent oxidation efficiency, but the HC is still about double the average for this year group. Also, NOx is commedably low, so the converters must be reducing very efficiently. These numbers are roughly comparable to Mike Tangas' 560 numbers posted earlier. I attribute the difference in CO2 to different fuel blends with a slightly different carbon to hydrogen ratio. Duke Duke |
#41
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Well, the car finally passed smog but not by much. My mech fooled around with it for an hour on Sat. and I watched. What seems to help the most was a hot cat.
If you recall, I replaced the cat but not the pre-cats. The odd thing now, at least to me after reading all the posts here, is that my O2 went from 0.00% with the old cat to 0.04% with the new. Anyway, here are my numbers: initial / last / max: 15 MPH CO2 13.50 / 14.47 / NA O2 0.00 / 0.04 / NA HC 187 / 122 / 126 CO 1.67 / 0.64 / 0.79 NO 460 / 250 / 1316 25 MPH CO2 13.70 / 14.60 / NA O2 0.00 / 0.03 / NA HC 166 / 77 / 101 CO 1.31 / 0.47 / 0.59 NO 417 / 239 / 1112 As you can see, the car is cleaner at a total cost of about $600 which included oil change, plugs, cat, an hour of mech time, and several attempts on the smog dyno. The car now has a two repreive until the nest smog. It will then likely become a doner vehicle or my permanent mexico ride at a friends home in cabo. Thanks to all who responded!!!!!
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E55, 300E, 65 Hipo Mustang, 66 Shelby GT-350, 69 Mach I, 66 Fairlane GT Conv., etc |
#42
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Typical KE test results - high or barely passing HC at 15 MPH. The 25 MPH HC is better due to converter heating during the 15 MPH test.
This is the first CA ASM test where I have seen O2 measured to the hundreth of a percent as apposed to tenth of a percent. Can you confirm this? Assuming your first test yielded accurate results there was no O2 and high CO because your mixture was way rich - outside the range where the O2 sensor and electronics could correct it to stoichiometric assuming the O2 sensor and electronics including EHA were functioning properly. My suspicion was that your converters were okay, but the mixture needed checking by observing the duty cycle and then going from there to correct a rich mixture condition. A hotter converter should also reduce more NOx creating more O2 for oxidation. Your NOx numbers are fairly low, but every little bit of additional reduction helps when your HC is at the ragged edge. You're CO is close to the limit indicating that the mixture is still marginally rich. If you still have the car up here in two years have it tested on a rainy day (if possible) and ask the tech to run the "tire dry test" - no load at about 2000 RPM for a minute. This will heat a converters a bit and hopefully provide a passing margin on HC at 15 MPH. The few hundreths of a percent O2 indicates that the HC could come down a few ppm if the converters were 100 percent efficient on oxidation to get the O2 number down to zero, and the hotter the converter, the more likely the probability that all the O2 will be consumed by oxidizing HC and CO. Duke |
#43
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O2
Duke
Thanks for the follow-up! Yes, the O2 is measured down to hundreths. I be happy to fax the before and after results to you.
__________________
E55, 300E, 65 Hipo Mustang, 66 Shelby GT-350, 69 Mach I, 66 Fairlane GT Conv., etc |
#44
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Duke here are my numbers for my 87 300E
25 mph- RPM 1671 15 mph-RPM 1737
HC in PPM 76 (148 is standard) 149 (152) CO % .17 (.94) .3 (.8) CO2 % 15.1 15 O2 % 0.1 .2 NOx 621 (1047) 1073 (1146) dilution 15.3 (>6) >6 last year's results HC 34 87 CO .2 .4 (.86) CO2 14.6 14.4 O2 13.8 these are the numbers 12.8 NOx 611 1107 dilution 14.8 14.8 2001 year high speed RPM 2650 low speed RPM 693 HC 21 36 CO .18 (1.2) .02 (1.2) CO2 14.9 13.2 dil 15.1 13.2 Thanks for any comments |
#45
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What kind of test was this - I/M 240? Our CA ASM test is a bit different, but I'm not familiar with I/M 240 at a low level of detail.
Also, what is "dilution"? Your results are similar to what I see with 103s on the CA ASM test - barely squeak by or marginally fail on HC on the first test (15 MPH), better at 25 MPH when the converter is hotter. Since you had 0.2% O2 on the first test, a hotter converter at the start of the test probably would have reduced HC and given you a little more margin. Your CO numbers indicate that the mixture is probably okay, so the O2 sensor, electronics and EHA are working. In the last several years that we have been subjected to ASM testing in CA the NOx measurements and standards are all over the place, and I can make not sense of them from test to test. I can only conclude that the CARB who controls the test software is still trying to figure out how to accurately measure NOx. Most recent tests indicate lots of margin against the limit, but yours is close to the limit. I can't offer any constructive comments on the NOx numbers. The degradation from the last year's test could be due to a colder converter, or degradation of the converter. They do degrade with use, but should last well over 100-200K miles if oil consumption is not excessive. The key is to have the converter as hot as possible prior to the test. Run it at 2000 revs with the A/C on defrost prior to the test. Go to a drivethrough place where you wait in line - like a car wash. Pick a day when the line is short or you can get right in. Duke |
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