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Old 03-06-2003, 12:45 PM
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Join Date: Mar 2003
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Question CANNOT SET LAMBDA ON 89 300e please help

i am trying to set the lamba on my 89 300e i have and open crcuit somewhere i have to diffrent fluke meters on the car fluke 88 is set to a fixed 70 and fluke 83 is fixed 30 i sent both meters to fluke to get calibrated they are both fine fixed 30 sends me to a coolant temperture problem and fixed 70 sends me either to the td pickup or crank postioning sensor how should i tackle this both meters are set the same on percent should since both meters are reading 2 diffrent settings what next thanks for the help
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Old 03-06-2003, 01:04 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Duty-cycle is often called On-Off ratio but if it were called Off-On ratio it would be the inverse.

Duty-cycle point of reference can be changed on most good meters (including those flukes). If the duty-cycle on is 70% then the duty-cycle off is 30%. You have to decide which period you are talking about.

As a point of reference your car should have a 70% duty cycle with the key on engine off. Verify and correct your point of reference on this number. (If your car is a Ca car it will be 85% instead of 70%)
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 03-06-2003, 01:47 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,804

Check section on Duty Cycle....
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Old 03-06-2003, 06:58 PM
pesuazo's Avatar
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Join Date: Oct 2002
Location: Near Raleigh, NC
Posts: 580
Wow, I just keep learning

Well, another lesson learned.
I was wondering why my Duty Cycle was at 30% with the ignition on engine off. After reading this post I realized my meter reads duty cycle, but the opposite way (Off/On). And no option to inverse the reading.
To make sure, I disconnected the coolant temp. sensor with the engine idling and it got locked at 70% (the manual states a fault for the device at 30%). Hmmm??!!, makes sense.
I tried another test for assurance, my meter reads a duty cycle at idle and 2500 RPM of 40-50%.
So in reality it is 50-60% (slightly lean); I measured the current at EHA and oscillates between 0 to +1.2 mA. A positive current means a compensation for a lean condition. (The opposite of -3 mA for a 38% rich condition, from stevebfl article in the DIY section).
I hope this helps someone out there.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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