[Diy_efi] Diagnostic TDC sensor on an old BMW (now with a view of signals)

Tomas J. Sokorai Sch. tsokorai
Thu Apr 13 04:01:19 UTC 2006

On Tuesday 11 April 2006 16:28, Torbj?rn Forsman wrote:
> On most german cars with a diagnostic "TDC" sensor, it will not give a
> signal at TDC but at 20? BTDC.

Thanks Torbj?rn!
Well, I did a quick & dirty check of the output as you suggested:


That's the variable reluctance sensor output captured with my laptop's 
soundcard ( I don't have proper oscilloscope :( )

I noticed some things:

1) Stock solid core wires and non-resistor sparkplugs are *very* bad for 
interference! Resistors on each end doesen't seem to help much. Note that 
even the channel that wasn't connected to the sensor (it wasn't connected to 
anything, just a 1cm pigtail emerging from the cable's shield) even picked 
the HV ignition signal. The VR sensor picked this HV signal even stronger 
than the ones from the damper timing marks.

2) My marks are too late timing-wise. I kept the "OT" (BTDC "Obere 
Totenpunkt"?) mark and did the other six relative to this one to emulate the 
needed signal for the old GM V6 DIS triggering signal.

3) The sensor has very low output voltage. This recording was using several 
K-Ohms between the sensor leads. BTW, what's the minimum triggering voltage 
for a GM DIS module?

4) What the heck is that lower strength sinusoidal signal between the timing 
signals?? damper irregularities?

Tomas J. Sokorai Sch.

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