What to measure and what to think about when running secondary trigger VR on a 3.2 or 3.3

Make a report of your measurements. All pins.

Report reasonably please

If you start to write these few things systematically, it's very likely the problem is revealed in no time. Rumbling on irc you waste much time, without result. This is very important. Reports without the most basic info, or to the wrong place is useless.

Emil's board - reply after the report requirements stressed on irc

v3.2, standard, Earlier trigged by primary trigger VR in a car.

Miska's board - onboard trigger setup is good now

Apparently, the 5cyl audi has more uneven fuel or air distribution than I thought ( if the lost spark is caused by those cyls leaning out - note that this is very low load, should not be dangerous). Possible causes:

The trigger is now good at cranking, h[2] fire order fixed now, and it sounds like it wants to fire up

It starts but loses sync soon, mdd04 pattern looks like ..PPnPPPPPnPPPPPnPPPPnnPPPPnnPPPPnnPnnPPnPPPP?

OLD problem - the 20k pullup on VR crankhome fixed this.

Analysis of [logfile] (R182 still onboard): primtrig events between sectrig-s:

after 2+81      (83)
after 2+51      (136)
after 3+54+10   (203)
after 15        (218)
after 2+50      (270)(0)
after 83        (353)(83)
after 2+51      (406)(136)
after 3+54+10   (...)(203)
after 15        (...)(218)
after 2+50      (540)(0)
after 83        (...)(83)
after 2+51      (...)(136)
after 3+54+10   (...)(203)
after 15        (...)(218)
after 2+50      (810)(0)
after 83        (...)(83)
after 2+51      (...)(136)
after 3+54+10   (...)(203)
after 15        (...)(218)
after 2+18      (...)(238) ?

It's obvious (last column is the total_sectrig % 270) that there is a periodicity of 270. But why are there 5 events (at positions 0, 83, 136, 203, 218) instead of 1?

Magnus board (aka 944_Driver on msnordic)

The problem is that interference from the starter gear sensor is triggering the secondary LM1815 circuit too. Cranking on the starter with the plugs removed and I get about 15 Vpp from the starter gear (quite high for cranking speed) sensor and 1.5 Vpp from the crankhome sensor. The interference found in crankhome signal is about 200 mVpp. Shielded cables are used all the way from sensors to the board.

So you are sure, that

I tried to decrease the starter gear senor output by applying a 1.5 kOhm resistor in parallel with it, but that didn't do much good. The interference got smaller but not much.

Is it possible to modify the circuit around the second LM1815 chip in such a way that the interference is ignored at all engine speeds? Just connecting the U12.5 pin to VCC will probably not fix it for all rpm I am afraid since the interference will get bigger with increasing rpm.

Does anyone know how Bosch solved the problem since it works fine with the stock motronic box?

It's very important to check that the secondary VR ("crank-home") is not inverted. The falling pulse-edge at the zero-crossing must be fast and sharp. This looks okay on the scope for me.

It's also possible that the signals mix in the magnetic field. If separate cables are used, and scope shows that primary is injected into secondary even with ECM removed, than this is the case. The 135-tooth can be reversed if necessary, so it can easily be subtracted from the secondary, with only just one properly sized resistor - but hard to size the proper value for this mixing resistor without a scope. (maybe also possible, looking at the mdd04 log output, and sweeping through possible values with a variable R: the midpoint of the R-range where the interference is removed is OK).

This is probably the problem. I found an old motronic (3.1?) schematic last weekend and it has some resistors in a network between the VR-sensor inputs. and I am rather sure the starter gear sensor is connected to pin nummer 8 and 27 in the system connector and crank home sensor to pin 25 and 26. That makes sens to me and matches with the pin out for my older box. The intressting part of the circuit can be found on the upper part of page 2. I wounder that kind of circuit 'S100' is? An older version of LM1815?

I have also taken apart an old motronic box from a volvo turbo (0 261 200 022) and the input circuit for the VR-sensor is not easy to understand. I have not been able to figure it out yet.

Magneti Marelli use a PI-filter on the VR-inputs. It is 18n capacitor from input to GND. Then 18K resistor in series with signal. And this followed by 18n to GND. The effect of this is a high pass filter. It will attenuate the signal at high frequencies. As it is used for a 6 tooth crank signal it will probably be appropriate to raise the cutoff frequency for higher number of teeth. Try substituting 18n with 3n3 or thereabout. It should be placed close to the connector or outside the box as there will be high frequency currents in the signal and GND paths between the filter and VR sensor.