[W126 Coupe] diagnostic port wire

[Dan Landiss]

Sharan Bains wrote:

> Dan,
>
> Yes, one end actually hooks up to the diagnostic port, at it's base.

The signals available at X11 are:
*Pin* 	*Function*
1 	RPM signal, 0 to 12 V, 4 pulses per revolution. A frequency of 43.3 
pulses per second corresponds to the desired idle speed of 650 RPM. (To 
check your tachometer you could measure the frequency at this pin and 
multiply by 15 to get RPM.) This signal is derived from the ignition 
amplifier and is synchronized with the low side of the ignition coil.
2 	GROUND
3 	Lambda on/off ratio, 0 to 13.6 V, 100 Hz. This is not a replica of 
the output of the oxygen sensor. The "duty cycle" in Mercedes literature 
refers to the percentage of time this signal is /low/. Longer duty cycle 
(lower average voltage) = lean, shorter = rich.
4 	Low (negative) side of the ignition coil. This is where to monitor 
the dwell angle of the electronic ignition amplifier, and is also a good 
place to view a reflected and attenuated image of the spark. This is 
about 50 VPP, safe for an ordinary oscilloscope.
5 	Hot (battery voltage) in Run or Start, *NOT FUSED!* This is actually 
the positive side of the ignition coil.
6 	Hot at all times, through fuse 2
7 	Shielded cable from TDC sensor. This is not the same sensor which 
triggers the spark control unit, but it could be used in a clever 
circuit with pin 1 to measure spark advance.
8 	Shielded cable from TDC sensor.
9 	Shield for pins 7 and 8.


> I am fairly sure the other end hooks up to the crank pulley, but want 
> to confirm.

Pins 7, 8 & 9 are a shielded cable to the TDC sensor, but NOT the one 
used for spark control.

-- 
:::::
A little rebellion now and then...is a medicine necessary for the sound health of government. --Thomas Jefferson, Letter to James Madison, 1787