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[Martin_1962]

What would happen to a DIS pack if one of the 3 ECU trigger wires was held to earth?

This would be a XnnXE V6 engine

[Marks DTM Calib]

Well quite obviously you would get 4 clyinder running!

You might also risk cooking the coil primary.

The ECU output should current limit but, how long it can stay like this without damage is any bodies guess

[Martin_1962]

Well quite obviously you would get 4 clyinder running!

You might also risk cooking the coil primary.

The ECU output should current limit but, how long it can stay like this without damage is any bodies guess

OK then the ECU survived but the coil pack failed - is this to be expected?

I need this for ammunition on my new web page where I am trying to get another site to remove images of my car.

[Marks DTM Calib]

Yes, the coils are not designed to carry a continuous current through them.....I would expect under this condition that the iron would saturate and it would sit there dissipating 10's of watts of energy (the primary winding will only be a few ohms). Say the winding is 4ohms.....your talking 36 watts!

What you have to consider is that the coil normally does not saturate, the dwell (current on time) is reasonably short and controlled by the ECU so as to get as much energy into the iron so that when the current is switched off, the back EMF is maxed out. Hence the power dissipated in the coil si generally small......but under these fault conditions its a different story!

The ECU should be fine as it is simply a controlled low side open collector type driver so only pulls the coil to 0V (chassis) any way. A short to 12V would have been an interesting one!

[Martin_1962]

Yes, the coils are not designed to carry a continuous current through them.....I would expect under this condition that the iron would saturate and it would sit there dissipating 10's of watts of energy (the primary winding will only be a few ohms). Say the winding is 4ohms.....your talking 36 watts!

What you have to consider is that the coil normally does not saturate, the dwell (current on time) is reasonably short and controlled by the ECU so as to get as much energy into the iron so that when the current is switched off, the back EMF is maxed out. Hence the power dissipated in the coil si generally small......but under these fault conditions its a different story!

The ECU should be fine as it is simply a controlled low side open collector type driver so only pulls the coil to 0V (chassis) any way. A short to 12V would have been an interesting one!

Can you write this in a usable form saying why a shorted to earth would kill the DIS in a short period?

Rather than me cutting & pasting

Thanks

[Marks DTM Calib]

What you need to do is consider how an ignition coil operates for max effect.

What we are trying to do is get maximum energy into the iron core using the minimum current in a short period of time (in the case of DIS equipped V6, the coil is fired once every revolution). What we dont want to do is saturate the coil because at this point the energy will no longer be passing to the iron (as it is saturated and hence the term) but will be dissipated as heat in the coil windings.

By storing max energy in the iron we will then get max voltage from the secondary coil when the primary current is shut off.

The coil setup has a permanent 12V supply on one side of the primary winding and the ECU switches the other side to 0V (chassis) to start the process of energising the coil. It tries to do this as late as possible so as not to hold the coil at saturation point for to long (in reality many of the integrated spark controllers detect the sudden rise in current at the saturation point and limit the current).

If we now consider a fault condition.

The Switched side (ECU controlled) of the coil is connected to 0V (chassis) permanently. The current will start to rise as energy is passed into the iron core until the core is saturated (this will only take a few miliseconds!). At this point, the coil is nothing more than a wire wound resistor and simply dissipates energy in the form of heat!

Now consider what is happening. The DIS pack has a primary resistance of about 0.5 ohms so the energy dissipated under such a fault is 288W!!!. Reality is that this figure will be considerably lower due to resistance of the wires etc but, the primary winding of a coil will NOT survive this fault scenario!

For further info for those reading this.

Now consider the standard DIS pack (and coil per plug to) failure mechanism is rusting of the iron core. The result of this is to considerably reduce the energy that can be stored in the coil and hence the ignition voltage drops as a result.

This can result in power loss, particularly at higher revs, and miss fires.....

[Martin_1962]

Thanks Mark that was usefull - just fixed a link I broke as well!!!!!