How to trigger BOSCH Monojetronic A2.2 ECU without Coil?

[ami8break]

Hello,
I'm going to replace dizzy+mechanical ignition with another ignition 'module' (DIY-CDI) and later the CDI should be fired by MSnEDIS. Engine is a TU3M (KDY) of PSA (Peugeot&Citroen), a couple of European SPI engines of late 80ties and early 90ties use the same ignition and EFI setup.

During the new ignition setup I want (have to) to squirt with OEM EFI ECU: BOSCH Mono jetronic A2.2.

My problem is that the OEM ECU doesn't work with with CDI output signal (primary side of coil). I tried also with OEM ignition module output (without coil which is powered by CDI).

Does anyone know how to trigger the BOSCH A2.2 ECU? Minimum voltage, trigger delay...?

Thanks
»Horst

[jakobsladderz]

You could try using a small transformer (perhaps a 9v primary wallwart transformer for example) and an ignition transistor (VB921 or equivalent) and build up a circuit to generate spikes equivalent to a normal ignition primary signal? Also, see if you can trace out the input circuitry to the bosch module, it may go in through caps and resistors to a low voltage input, you may be able to modify the module or inject the signal in somewhere other than the normal input.

A few ideas anyway.

Cheers

[ami8break]

Hello jakobsladderz,
thank you for reply.
The project is parking so I haven't continued to get the ECU triggered.

I'm not an EE so it's difficult for me to develop a circuit by my self.

You think I can feed a wall wart transformer http://en.wikipedia.org/wiki/Wall_wart by an OEM ignition module (which includes inductive sensor pickup condtioner), right?
And then?
Should I connect the secondary side to a ~5W power resistor (how many Ohm?) to discharge to ground and to the ECU trigger?

I thought also to reverse engineer the ECU trigger (protection) circuit to trigger it with a reduced (12V-->5V) MS injection signal, but I'd prefer to avoid modification there.

»Horst

[jakobsladderz]

Actually, after considering the secondary voltages that might be reached I realise it's probably not such a wise move doing it exactly that way, something like 1230 volts or so (perhaps more), the insulation may not hack it.. Along the same lines though an inductor of 3-4 mh (try crossover inductors) in parallel with a 300-400 ohm resistor would do. A resistor may be needed to limit the current to 0.5-0.6A..

______12v
| |
/ (
\ 300r ) 3-4mh
/ (
| |
|______|to ECU
|
/
\ >10r 10w...
/
|
to ignitor.


SHould work

[ami8break]

Hello jakobsladderz,
thank you for ASCII graphic circuit.
Just to confirm that I understood you:


I tried to find something about 'crossover inductor' - but failed.
Could you please give an example how the look like. Which specificatieon beside 3...4mH is important: http://search.digikey.com/scripts/DkSea ... s=inductor

Thanks

»Horst

[jakobsladderz]

The circuit looks right to me. Essentially the idea is to simulate a coil primary voltage without using as much power. Tune the current draw of the circuit with the 10 ohm resistor (bigger for less current) and tune the secondary voltage with the 300-400r resistor (bigger for more volts).

by crossover inductor I mean in a hi-fi or car speaker system crossover but don't worry, any inductor with the right specs should be fine. Essentially the specs to look for are the maximum current (>0.5A), the dc resistance (anything up to 4 ohms is fine) and the inductance (4 millihenries, mH). A current of 0.5 amps would be enough (use a 24-(inductor dc resistance) ohm resistor instead of 10ohm resistor get 1/2 amp at 12v, eg for a 4 ohm coil use a 20 ohm resistor). inductance of 4mh will give ~175v with a 350 ohm resistor (in the 300-400 ohm position).

Cheers,
Duncan

[ami8break]

Hello Duncan,
thank you very much for explaining the principle of the circuit.
I hope to get it tuned (with a little help from my EE friend)...
»Horst