Why keep getting wide different "duty cycle" readouts for fuel mixture???
 

Hi, I have some rough idling and found out fuel mixture needed to be readjusted. After it has been readjusted by my mechanic the rough idling is better but still remained. I try to adjust it myself so I bought a Sear Multimeter 82334 with duty cycle. This is the first time I have used a multimeter.

I set the function dial to frequency/% and select % in display.

Then I put the positive lead (red) into #3 in X11 and the negative lead (black) to the driver side's plate (ground) that hold the spring into place.


With the engine running, parked and temp at 82 I saw the # on the multimeter display fluctuated and then stopped (frozen) at a number and doesn't change anymore. I tried several times and keep getter a very wide range of frozen numbers 99, 100, 51, 27, 34 without any adjustment to the fuel mixture. So I don't know what is going on let alone trying to adjust it close to 50%.

Please tell me what have I done wrong??? Thanks very much.

Rick

Use the #2 hole of the x11 it is ground,pin 3 & pin2, see if that helps. If not you May wish to do a search and take readings from the EHA. and the potentiometer,all with the same meter at different settings.

I have a similar meter... read this thread and it will help you.

http://www.peachparts.com/shopforum/showthread.php?t=158920

Well have you had any luck with your Idle problems? I reread your post and I felt so dumb, The one thing I forgot to say,Oxygen sensor. If you are getting such wide swings don't forget to check the closed loop for ox.

update: I have tried to adjust the air/fuel mixture all this time using X11 connector with my duty-cycle meter. Well, I still haven't succeeded. During that time I have changed O2 sensor and tried measuring pin#3 voltage to get a ratio using this fomula 1-(V#3-V#6)x100. When I used duty cycle method I kept getting some fluctuation then goes to 99 or 100 then 00.00. When i used the voltage method I keep getting pin#3 as having voltage 2.49v no matter which way I turned the adjustment. I know I had the adjust screw connected because I could hear the engine sound and vibration changed few seconds after my adjustment. All these with O2 sensor disconnected to get a more accurate reading.
I finally broke down and went to a local MB shop. He adjusted the fuel mixtured for me but he told me he didn't use the X11 instead he used something on the other side (passenger side) of the engine compartment. I don't how he got his reading but the car is very smooth now. If anyone here knows what he used to read the mixture instead please do tell.

thanks

Rick

The inexpensive Sears meter I got will not read if the black lead is grounded. Don't ask me why, but just putting the red lead in #3 and leaving the black on swinging works fine.

I'm probably not smart enough to figure this out, but the car runs great.

Peter

Adjusting Idle
 

I have had a difficult time adjusting the duty cycle to 50% also. I have the Sears meter. I am going to try to leave the black lead unconnected to any ground to see if that works.
Is there a way other than the CO tower adjustment to change the Idle speed in my 190E 16v? I dont remember which other adjustment might raise the idle speed and I have had bad experiences just randomly adjusting cables and screws to start turning things too much. I will break out the manuals I have to see if i can figure it out this weekend.