We are hoping for some real data here!

Can you get your hands on a multi-meter of some sort? If you can:

1. Set function to DC Volts on a scale where you can read to nearest tenth of a volt.

2. After driving car (it needs to be good and warm), and with the car idling, measure the voltage across the + and - terminals of the battery. Remember the reading.

3. With the car idling, put the positive lead of the meter in Pin 3 of the diagnostic socket, and the negative lead in Pin 2. Remember the voltage reading.

4. Have someone bring the RPM up to 2500 and observe the voltage reading.

5. You can now compute your duty cycle (DC) like this:

DC in % = (Battery Voltage - Pin 3/2 Reading) / Battery Voltage * 100

Example:

Battery Voltage = 13.5
Pin 3/2 Reading = 7.5

DC = (13.5 - 7.5) / 13.5 * 100

Duty cycle = 44%

6. With engine at idle, oberve the Pin 3/2 voltage for a few minutes and see if it changes in a pattern corresponding to what the engine is doing.

Go for it! Let us know the results.

Note - if the meter has a Duty Cycle function, you can read the numbers directly. Every meter has a voltage function, though, so I decided to use this method.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe