Using M800 to fire Saab Direct Ignition Cassette

[ejenner]

Hi there, I'm trying to use my M800 to fire a Saab ignition cassette and can't get it to work. I'm using the 'test outputs' function to show me if it's sparking or not. Plus the obvious test conditions where I have a spark plug sitting in the cassette with the cassette removed from the engine and the body of the spark plug grounded so a spark can be produced.

I've been doing as much reasearch as possible on the DI cassette and although there is contradicatry information explaining how to trigger it... I have found through testing that the trigger wires (there are 4 of these, one for each coil) need to be grounded to make the plug fire.

When I have checked to see what the Motec is trying to do it seems the Motec has the trigger wires always grounded. When it wants to fire a plug it pulses the trigger wire, either with voltage or just a disconnection from ground - not something I would be able to measure with a standard voltmeter - so to the best of my knowledge it is switching between 12v and ground when the pulsing starts for testing the plug using the test function. If I try and test a diferent coil then the plusing moves to the coil that I'm trying to test.

So the problem seems to be that the Motec is always grounding the cassette unless trying to trigger it.

There is one more test left to do and that is to try and disconnect 3 trigger wires and leave one remaining. Under these conditions, if all my other assumptions are correct, then this should work to pulse the one remaining coil and make it fire. I guess we are seeing here that the with all the trigger wires always grounded there is never any chance for the cassette to build up any charge for firing the plug.

If any one can help with this then that would be genuiis. I will come back and post my answer if I find out what to do elsewhere.

[RossB]

Do you have any wiring information for the coils? Have you wired in an ignition module(s)? The logic of the output on the M800 is determined by the "Ignition Type" parameter in the ignition setup, the output is intended to trigger a coul via an ignition module or a coil with a module built in.

[ejenner]

Nathan at the UK technical department got a couple of coils from me on Friday afternoon. So he set one up on the bench and made it work. The reason I couldn't get mine to work before was because I was trying to use a broken coil-pack. Initially this was causing problems for Nathan as well. He was seeing a very small spark from this ignition pack but when I was there yesterday evening I suggested we tried the other coil pack. That worked properly and now we have all the parameters for getting this going.

So in case anyone else searches on these forums for info to get this running... here are the details:

Ignition type = 1

Number of coils = 4

Dwell time has to be adjusted according to battery voltage = 2.0ms seemed to be the correct dwell time for normal battery voltage. Lower battery voltage needs a longer dwell time. Nathan thinks this is very unusual for a CDI unit. But it was confirmed on the test bench and we repeated the test several times.

Pin-out Data:

Pin 01 = ECU Monitors Charge Voltage to the Capacitor
Pin 02 = Trigger Cylinder 1
Pin 03 = Trigger Cylinder 2
Pin 04 = Trigger Cylinder 3
Pin 05 = Trigger Cylinder 4

Pin 06 = Ground
Pin 07 = Voltage varies according to amount of knock detected – ion sensing
Pin 08 = Position of engine – cylinders 1 & 2
Pin 09 = Position of engine – cylinders 3 & 4
Pin 10 = Battery voltage when ignition on or when cranking

In theory the ignition cassette has the ability to sense piston positions and knock detection via pins 7, 8 & 9... When connected to a Saab Trionic ECU it does this. But with the Motec I think it will be too much trouble to try and get this working as there won't be enough benefit. I'd like to remove the cam sensor and use pins 8 & 9 for position sensing... but maybe that's something for the long term rather than something I want to sort out now.

[ejenner]

Actually. It doesn't work. Only works with one trigger wire connected. If you connect all four trigger wires then it won't work. Not sure how to get it working now. Obviously it's no good having only one trigger wire connected because then only one plug will fire.

I think the problem is that the ignition coils are fired by grounding the trigger wire. But the M800 is grounding all triggers all the time. Except when firing and then it pulses. Or possibly vica-versa - the coil is fired by sending 12v to the trigger... although I think that's unikely. Whichever the case, the continuious state of the non-firing ignition outputs from the M800 is preventing the capacitor from charging.

Anyone have any ideas for a work-around?

[Mazi]

Adjust > General Setup > Ignition > Setup > Ignition Type (IGN) ->>> F1

[ejenner]

Don't forget. Motec UK are involved here. We have looked at all this sort of thing. But if that happens to be the answer then I will certinaly post back here with congradulations!

[RossB]

Didn't realise that it was CDI. The dwell will not need to vary with battery voltage, I think the factory ECU runs a 2.5ms dwell all the time. The outputs on the M800 are not grounded all the time, they are only grounded during the dwell time.

[ejenner]

Are you saying it's grounding all of the outputs during the dwell time?

Nathan was testing this cassette here and as we varied the dwell time the intensity of the spark varied. Not enough dwell and the spark would be too weak. Too much dwell and it would first not fire and then double-spark. So Nathan built a settings table that shows what the dwell time should be for various battery voltages.

Battery Voltage 5 6 7 8 9 10 11 12 13 14 15

Dwell Time 6.6 5.5 4.7 4 3.4 3 2.7 2.4 2.2 2 1.9


The fact that the Motec is doing 'something' with the 3 non-firing trigger wires is the important bit of information here. As I'm only 'entry-level' at this game I might say 'ground' when I mean 'voltage' on occassions. So if what I'm saying does not make sense then I probably don't mean what you think I mean.

In this case. The Motec can eaisly fire 1 coil if you hook up only one trigger wire. If you hook up all trigger wires then we have an issue where what the Motec is doing with the 3 wires for coils that it isn't firing is causing the capacitor not to charge right from the beginning. So there is never any chance to build up voltage to fire any coils. This is what happens when all 4 triggers are connected to the ECU.

[RossB]

No, it only grounds one output at a time. If Nathan has come up with those settings they should be ok.

[ejenner]

If you put a probe on an earthing point on the chassis while you are firing one of the trigger wires and the other probe on a non-firing trigger wire you will get a continunity signal.

The Motec will fire one coil with one trigger wire just fine. But with two or more triggers connected no sparks will fire.

This is the problem.