After reading all the posts on checking the duty cycle, I purchased a Sears Multimeter model #82139. My initial readings on closed loop operation was approx 35% indicading a rich setting. I suspected something was up when the number would drop while turning the adj screw CCW. The only way I could get the number up was to richen the mixture by turning the screw CW (totally backwards).

My local Indy hooked up his dedicated duty meter and said I was lean at 65%. He turned the screw CW and set the mixture at 45%. I tried my meter again and found out the only way I could get it to read accurately was to put the black probe into the #3 pin at X11, and ground the red probe into the #2 pin. (totally backwards again).

To pre-answer some questions:
Batteries - in correctly
Leads - in correct sockets on multimeter
Beer - still in the fridge

I contacted the meter manufacturer and we verified that the meter is functioning properly otherwise. He suggested to remember to reverse the leads in the future. I could still return the meter, but would they all behave the same? All I have read here indicate that the #3 pin goes to the red probe.

Anybody else run into this?

Duty Cycle reading and questions......

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Benz uses a reverse duty cycle measure. It is ONFFmeasure, vs ON..

"Mercedes has chosen the less common definition of "duty cycle" in this case. They are referring to the percentage of the entire pulse period during which the voltage is zero, not the time when it is near battery voltage (mine was +13.6 V when the battery was +14.0 V). In other words, if the pulse rests at ground for 7 milliseconds and then rises to +13.6 V for 3 ms, the duty cycle is considered to be 70% (see oscilloscope trace at right). "

I'm sorry Arthur I am math disabled and have a hard time translating formula into a clear grasp of reality.

I am under the impression that the early M103 engine X11 port is properly read (by a sears type multi meter with duty cycle setting) with the (+) lead in pin #2 and the (-) lead in pin #3... this is due to the % ON bias of the multi meter in question?

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Marty,

I had forgotton about that earlier thread started by Merkey. I do have some differences though. When I put black probe into #3 and red probe into #2 (as in his second picture), I get a 30.0% reading. My MB WIS does spec a KOEO30% reading with coolant temp <70 deg, and 70% >80 deg. This is for a Federal/CA car as of 9/89.

I therefore attribute this baseline difference to him having an '88 and me a '90.

I just noticed that the second link in my sig was not working and fixed it.
The second attachment in that link: http://www.peachparts.com/shopforum/attachments/tech-help/24327d1109717988-duty-cycle-84%25-what-does-mean-2fd2.jpg
...is exerped from MB service CD and indicates that, to recognise the control unit the Key On reading should be 70% (federal) or 85% (California) ,,,

I have assumed that If the test method gave the correct reading at this stage it was via that method that it would give the correct duty cycle reading.

Reading through many posts on this subject however has not assured me that one method was universal or that there is a well defined MY change-over to a different output method. Perhaps 9/89 is the date.

90's were built in 89... what is your build date? (driver door panel)

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

My sticker on the door panel is gone. I know that I have the later build date because my VIN is in the later group of numbers. My research and experience-to-date also indicate that the later production group had many changes related to the duty cycle.

Merkey ('88 300te) and I ('90 300te) have different ECU's. His is the 25 pin and mine is the 55 pin. Additionally, my LED does not go into a "continuous on" mode. I also verified my readings with a '92 300te here in CA.

So, many of those writeups that I have read on preforming duty cycle readings shoud be modified for the later build group.

And yet your duty cycle #'s are accurate with your meter in reverse poles.

I would like to know who reads (black 2 red 3, Y/M/M, and meter type) and who reads (red 2 black 3, Y/M/M, and meter type) so we could find out if there is a pattern here.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

The manual for that meter states the duty cycle measure is for ON pulse width, from 100us-100ms [ which is 0.1%-99.9 %]
My info shows Benz uses Off cycle for duty percentage. [ meaning a correct reading with that meter requires reverse polarity of leads]

I guess I'm just get off my @ss and read chalenged.
Thanks Arthur that helps a lot...
Mercedes always does it one way but meters vary...

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Mark....

Clearly for me the mistake you are making is in your first post....
Step 3.........

__________________
2009 Mercedes ML320 Bluetec

Arthur,
I could not find anywhere in the manual where it states that the meter uses the ON pulse width. I called EXTECH (mfg for this Sears multimeter) and tech support confirmed that they have no documentation stating such. I relayed my story of checking the meter against the Indy MB mechanic's duty meter and he concluded that the meter appears to be displaying ON vs OFF as a %.

Based on this info, I would suspect that we have a few members of this forum that are running lean at 65% instead of the 45% they think they have their car set at.

Interesting...

<>

Well , how I read that is PULSE WIDTH is ON , because NO pulse width would be OFF.[ meaning NO signal]

The point I was making is BENZ specs for DUTY CYCLE is the opposite of American duty cycle, where Benz % specs are OFF %, rather than ON %.


I will do some homework and find that info..I had a site that explained better than I ... I just have to re-find it..

.anyone else have that info????

My bad typo. Sentence should read:

.... I would suspect that we have a few members of this forum that are running lean at 55% instead of the 45% they think they have their car set at.

You can verify by just using normal voltage and the formula!

__________________
~Jamie
_________________
2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....