I made a previous thread about how my 93 190E 2.6 acted like it was running lean. I went and got a spare EHA valve from a friend and swapped them out. Car runs ALOT better now, but still runs slower than usual and coolant temps are slightly on the higher side.

I went and measured the duty cycle at X11 on pins 2 (red positive DMM lead), and 3 (black negative DMM lead)

It was interesting to get the duty cycle working on my car, so I will post it here so someone in the future can follow these steps.

Getting Duty Cycle Working:
I've read that to get the duty cycle readings to show up on pins 2 and 3, I have to do key on, engine off and I should see 85% for a california car. However, I got 50%, each time I took the key out and put it back in the switch.. Then I also read that I had to press the X92 led button for 4 seconds, release, and repeat again to have the red led on constantly. That didn't work either. When I cranked the car to start it up, it showed 70% while cranking, then went straight to 50%. I thought the O2 sensor broke, since thats what everyone was saying. I spent some time reading the O2 sensor voltages, but the O2 sensor was working properly with heater wires at battery voltage and fluctuation in the signal wire. I went back to the X92 port, plugged my leads in (2 - red positive, 3 - black negative since people were saying Mercedes runs the opposite duty cycle) and to my surprise, I was getting something other than 50% and was fluctuating. So then I figured out that the engine needed to be running for at least 30 seconds at operating temperatures for the duty cycle to appear on my DMM.

anyway, I replaced the EHA valve and wanted to make sure it was adjusted right for correct fuel mixtures. at idle i am getting around 34% with fluctuation, and at 2500rpm it is nearly 50% with fluctuation.

are these acceptable values? i still feel like my car is running lean. I am going to tweak the EHA valve a 1/4 of a turn and read the duty cycle again to see if anything changed. any thoughts?