Took the car in for biannual emmissions. Slightly higher CO, HC than 2 years ago, seemed to be running rich.Passed OK, but Hooked up the Voltmeter and go a 5.5v average-spec says 2.4 to 4.8v or so. Book also says that lean=higher voltage, rich =lower number. I should have been lean, why did I get a "rich" (higher HC & CO) symptoms but showed lean? Does this number get effected by altitude? I live @ 6000ft, I am told the altitude sensor leans out the mixture, but how? Any ideas on how to figure out? Are there corresponding Duty Cycle numbers instead of voltages? Thanks Scott BTW Does Lambda fluctuate much off idle? Under load? If so, whats normal?

Lots to learn and most has been discussed endlessly.

Lambda control in closed loop exists for O2 voltages between .2 and .8v for MBs. Some cars use 5v O2 sensors but not MB.

Duty cycle refers to the level of correction when viewed dynamically. Middle of range would be 50%. Duty cycle as a constant is used as a fault code.

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

not an expert on this by any means but i believe higher voltage means rich, higher duty cycle means lean. two different ways to look at the same signal.

I understand the duty cycle theory, been through it on my 300E. But the 1986 2.3 engine only posts the voltages in the factory manual. Is that the only way to determine what is going on or is there a corresponding duty cycle number as well? One thing that has not been discussed at all is how altitude correction devices are employed by M-B. (ie how it effects EHA numbers) The theory part of the factory manual hasn't said HOW it makes its corrections. And precious little on how to test for it. I have read your articles in depth and appreciate your input on the board....Scott

"But the 1986 2.3 engine only posts the voltages in the factory manual. "

I do not understand this sentence. Actual values can vary model to model and I don't have them all memorized. I do lots of my testing by feel and recognize the particulars as I test.

Early 190's don't have the ability to go negative with EHA current. An 84 or 85 would fit this catagory, I'm not sure on a 86. The all should give integrater values in duty cycle. Whetehr they can express a fault code by duty cycle also varies. If you get a fixed duty-cycle other than 50% you probably have a fault code indicated.

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

So what was it 2 years ago? Slightly higher to me is about 20%, whats your definition? Its either rich or it's not.

I speculate that your cat is just not as efficient as it was 2 years ago and the higher readings have nothing to do with the A/F control. How many miles have you driven in thes past 2 years? How old is the cat?

To answer the question on altitude, there is a little capsule that is usually lcated in the passenger foot well area that compensates the CIS system. It feeds info to the CPU.

Peter

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