I bought Sears multimeter 82139 with duty cycle and hooked it up (still trying to track down some mileage and hesitation related issues). I am getting 70% static reading at pins 2 & 3 of the X11, 50% readings when the car is first started, and then after operating temp is reached (85-90 C), I am getting readings of 28% to 36% at idle and 41% to 49% at 2500 rpm. Does less than 50% indicate a lean or rich condition?

What does it all mean? I have read thru the Landiss reading and probably all of the posts and I'm still not clear...

I would like to test the EHA ma's, but I don't have the harness - can you still get it? I found it on the Baum Tools page, but it doesn't indicate that it works for the M104 motor???

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

28-36% is too rich but 41-49% is in the right region.

My 300-24 (104 engine) is set to 50-54% at idle and around 60% at 2k5. Overall performance and miles per gallon are very good.

Oddly, my static reading is now 50% but it was, correctly, 70% before and I cannot understand why.

Some more knowledgeable people will be along soon.

Bonne chance.

RayH

Anyone else offer some help here?

I measured the duty cycle last night and again this morning and both times the readings at 2500 rpm and at idle were similar - 41%-49%. This indicates a slightly rich mixture - right?

The ambient temp was cooler for both of these last measurements - don't know if that has anything to do with it, or not??? I really notice a difference when it is hot here...

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

I have read just about everything I can on adjusting the mixture and reading the duty cycle - and I am still lost!

Just took some additional measurements - I put the red lead on pin #3 and the black lead on pin #2 and I get a a static reading of 69.9% - so far so good. Start the car and readings fluctuate around 50% until the car reaches operating temp - then readings go from 33%-41% at idle and 35%-43% at 2500 rpm. So I'm running rich, right?

So I check the volts and they read 4.7v-5.7v at idle and 5.1v-5.9v at 2500 rpm - BUT, according to the Landiss formula that doesn't make sense! A 4.7v reading should correspond to a 66% duty cycle and 5.7v should correspond to a 58% duty cycle - backwards of what I am getting! What's going on here?

I have read about some folks getting opposite readings with red on 3 and black on 2, but I'm getting the correct 70% static reading with red on 3 and black on 2...

I'm lost?

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

I'm wondering if you know that Mercedes bases duty cycle on the amount of time at zero volts rather than the other way around, as is more conventional. In other words, you're measuring the amount of time at zero, as a percentage of the total cycle, just the opposite of what you might expect. That's why the duty cycle formula requires subtracting the readings from 1 to arrive at duty cycle values. Sorry if this is obvious to you.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Nothing is obvious at this point! I have read thru that - just not sure what it means and how to 'translate' it to my current situation.

So, should I be reading 30% duty cycle at static (KOEO)? Do I reverse the MM leads - black on 3 red on 2? That will give me a 30% duty cycle...

Am I running rich or lean?

I guess my voltage readings are correct then...

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

You don't sound lost!

You just sound a little rich.

You should see 70% duty cycle ignition on, engine off.

Try to adjust the duty cycle from where you are (average of, say, 38%) to a value that fluctuates around 50%. I have done almost exactly this (average around 56%) and the car's running very well with reasonable consumption and nice clean spark plugs.

If you have a Duty Cycle meter, don't concern yourself with voltages.

And finally, yes, less is richer so I am suggesting you make the mixture leaner.

RayH