Wasted Spark Coil Pack Fault

[toddster900]

Hi Everyone

I recently had a coil pack fail highlighted by a misfire on cylinder 1. I took out the plug, turned over the engine and sure enough no spark on cylinder 1. I then checked the spark on cylinder 2 and it was perfect so i swapped the plug and lead on cylinder 1 and 2. The fault stayed on cylinder 1.

I then emoved the coil pack and both primary and secondary coils tested fine for resistance but as I knew the leads and plugs were good I knew it could only be the coil pack and sure enough changing the coil pack cleared the fault.

So my question is how can a wasted spark coil pack fail in such a way that the spark is lost on only one cylinder? If cylinder 1 plug was not sparking how was the circuit being made for the companion cylinder?

The only reasonable conclusion i can come to is that although cylinder 1 was not sparking it was still somehow conducting allowing the circuit to complete through both plugs. If this is the case what failed in the coil pack that only affected the cylinder 1 spark and not its companion?

Am I missing something here?

Thanks

 

[plugsandsparks]

How many cylinders and what is the firing order ? - Are you sure cylinder 2 is the paired spark for No1 ?

 

[JBW175]

Is this on an outboard motor by any chance?

 

[toddster900]

Thanks for the replies!

The fault is on an 02 plate Ford KA.

The firing order is 1-3-4-2. The companion cyliner is cylinder 4. I mentioned cylinder 2 as I tested the spark on that to check the plug and lead were good before I transferred them onto cylinder 1.

In hindsight I now realise I should have checked the spark on cylinder 4 but it wasn't until I had replaced the coil pack that I started to wonder what was actually wrong with the coil pack.

Any ideas what could have been wrong with it?

 

[JBW175]

Broken termination inside the coil pack on number one cylinder where the HT lead joins it.

 

[plugsandsparks]

As you did not test No4, its difficult to tell but it could have been the input stage of coil pack which takes its trigger from the ECU.

 

[toddster900]

I can't see it could be a broken termination on cylinder 1 as if that was the case I there would have been no spark on cylinder 4. If that was the case not only would it have not run but I would also have been getting an error code on cylinder 4 too.

I also don't see how it could be a primary coil. If that was the case I would have again been missing both cylinders 1 and 4. I also tested all four coils for resistance and the values were all within spec.

I just can't see what could have been wrong with the coil pack given the symptoms but I also know changing it resolved the problem.