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1982 Mercedes Benz 240D
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156 Posts
Discussion Starter #1
I have done research on adjusting the air/fuel ratio but it seems something still isnt right. From what I have read the voltage across the sensor at the x11 connector should very by a volt or two. I am getting readings between 3.8 and 4.5 and nothing more. At first it was over 5 volts and reaked of gasoline from the exhaust. That has deminished a great deal but still has the smell. My O2 sensor voltage is dancing as it should so I know that is doing its job.

The reason I decided to go for this adjustment was I had some consistant power loss. In set intervals the car would drive normal then have a sudden power loss followed by power gain in a set pattern. similar to the duty cycle pattern across the lambda on a scope.

any ideas?
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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5,447 Posts
Sypherz....could you do me a big favor and tell me the procedure you did to probe the O2 sensor? I am getting some odd readings that I cannot understand. I just want to make sure I am not doing something stupid.

That would be great if you could.

3.8 - 4.5v fluctuating works out to be ~28% which is far too lean. In your case though, your DMM may be reading it inversely which would make more sense....so 72% rich...hence why if you raise the mixture it becomes WAY to rich.

Try leaning out to 5.5v and see how the car feels. Counterclockwise on the mixture unit.
 

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1982 Mercedes Benz 240D
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156 Posts
Discussion Starter #3
Ill have to find the formula that I used but my calculations put me at ~48%, and the fumes of gas diminishing helped me feel as if that was accurate. Initailly when I was 5+ volts the gas fumes was quite high.

I used a multimeter with the positive in pin 3 and the negative in pin 2. From that reading with the motor hot it was dancing right at ~5 volts, and I judged it as I turned the adjustment screw CCW till I hit the high 3's, low 4's.

I dont remember the O2 reading but I do know it was tolerable at the time. I still have the airbox off so I can redo the measurements if you feel something is still off.
 

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1982 Mercedes Benz 240D
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156 Posts
Discussion Starter #4
I want to add that I just replaced the spark plugs. The old ones were not the recommended plug and based on the copper hue I am assuming they were too hot as well. It seems to idle better than it did before however the power loss still exists.

I checked the plug wires in the dark and I see no signs of arc. Air filter is new. Fuel filter is questionable.

It always has had some issues starting. Sometimes I have to allow the motor to cycle for nearly 5-10 seconds before start unless I pump the gas pedal. higher RPMs cause the gasoline odor to return.
 
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