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Old 08-07-2003, 05:46 PM
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Mike Murrell Mike Murrell is online now
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Re: Duty cycle

Originally posted by azhari
With your fluke dialled in to measure DC voltage, measure your battery voltage (V) with your engine running above 80 deg C.

Next, take the cap off the diagnostic port X11 (the round capped connector on the injection module).

Put the black probe of the meter to ground or battery negative and pit the red probe into pin 3 of the X11 port.

You should get a voltage (X) reading.

The duty cycle (%) is (X/V) x 100.

Eg. if your battery voltage is 13.8V (V) and the voltage at pin 3 (X) is 5.5V, then the duty cycle is (5.5/13.8) x 100 = 39.8% (slightly rich).


The formula above looks similar to the one at the following WEB site with a slight exception that affects the answer significantly.

When I have time, I'm going to get a reading using my Sears duty cycle VOM, then try the approach here using a standard VOM and formula provided; them use the standard VOM and the formula at the Landiss site.

In the end, I suspect it's simply easier to use a duty cycle VOM and leave the math to the engineers who invented the Bosch CIS-E system, but I am curious.
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC

Last edited by Mike Murrell; 08-07-2003 at 05:54 PM.
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