Sorry for asking this again, but I have doubts and nobody has noticed a previous posting about this.
I want to adjust the fuel mixture of my 190E 2.3 properly. From some postings here, I must monitor the duty-cycle reading at pin 3 of the X11 connector while adjusting the 3mm allen screw in the fuel distributor.
Should I do this with or without the 02 sensor connected? What value should I look for and at what engine speed?

Thanks!!!

There has to be a thousand hours or more of reading on this subject in the archives.

From your question, the first key word to look up is "closed loop". To electronically adjust these cars you have to understand closed loop. Or I suppose you could just do it and not know what you are doing. Do the search to find real knowledge.

Do it with the O2 sensor plugged in, hot and running in "closed loop" control. The proper duty-cycle is an average of 50%. My preferred setting is 35-45%. Use a search to find out why both readings will give exactly the same mixture once closed loop operation is in effect.

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

Thanks.
I can assure that I have spent hours reading the posts in this forum, but still had doubts.

My main question is, why some people (like you) prefer 35-45% duty cycle if (due to close loop control) every setting (between the 0 and 100% limits, of course), will lead to the same mixture?
Is that because under load conditions you must have margin to enrich the mixture even more?
In my case at 2000-3000 rpm the reading is around 25%, that seems the reaction to a lean basic (open loop) setting. Am I right?

I wonder what happens when my engine is at full load... is there enough margin for the ECU to enrich the mixture?

Thanks again.

Look at:

www.landiss.com/mixture.htm

Duke