Sears Multimeter #82139 for Duty Cycle Check - PeachParts Mercedes-Benz Forum

Mark M · #1 08-09-2006, 05:17 PM

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?

A264172 · #2 08-09-2006, 05:23 PM

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

Arthur Dalton · #3 08-09-2006, 06:22 PM

Quote:

Originally Posted by A264172

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

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). "

A264172 · #4 08-09-2006, 06:43 PM

Quote:

Originally Posted by Arthur Dalton

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

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?

Arthur Dalton · #5 08-10-2006, 02:31 PM

Quote:

Originally Posted by A264172

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?

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]

A264172 · #6 08-10-2006, 03:15 PM

Quote:

Originally Posted by Arthur Dalton

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...

Mark M · #7 08-11-2006, 10:41 AM

Quote:

Originally Posted by Arthur Dalton

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]

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...

Mark M · #8 08-09-2006, 06:51 PM

Quote:

Originally Posted by A264172

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

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.

A264172 · #9 08-09-2006, 07:16 PM

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/attachment.php?attachmentid=24327&d=1109717988
...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)

Mark M · #10 08-09-2006, 07:53 PM

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.

A264172 · #11 08-10-2006, 01:58 PM

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.

crhenkel · #12 08-08-2007, 08:45 PM

Ok so I am in pure hell. I have a very nice 1986 W201 2.3-16 and I decided after all the reading I did about duty cycle and CO setting to check mine out. SHe smelled a bit rich so I thought, hey, I'll do it the right way and buy the meter and test it. WRONG!
I have read everything on the forum about setting the CO by duty cycle and by EHA. I added it to what I already have learned and already knew and put it all together and still have no explaination at to why I cant get the readings correct. I cant even get the 70% or 85% to read indicating a Federal or California car with ingition on and engine off. When I do this simple test at the X11 diag connector on the drivers fender well, I used both the 2-3 pin setup and the 3-2 pin test. Red and black leads in 2-3 and then in 3-2 and neither shows 70 or 85 percent. Red in 3 and black in 2 shows 50.6% plain as day al day. Red in 2 and black in 3 shows 49.8 all day long. Using a different ground instead of the 2 pin gives the same results no matter what. I have a spare ECU computer, correct part and numbers for the car, an exact duplicate and a working pull. I swapped it and is shows the exact same values for duty cycle. If some one wants to tell me I have two bad ECUs that went bad wit the exact same resistance, go ahead, but I think the ECU is good. Can anyone clear this up?

When I start the car , the readings all go way in to the 90's and fluctuate from the initail 50% after the warmup period is over. The o2 sensor is new and the eha is relatively new and does not seem to leak. Other than the car exhaust smelling a bit rich, the car runs great. maybe the idle is a bit low, instead of 900-950 as I think the manual states, it might be in the 750-850 range. But, no stalling, easy starts col and hot, no overheating, ac works fine, etc....just screwy readings that match nothing I can read or hear from anyone else.