Hello everyone,

I have a problem with our Enduro 25 which I cannot figure out at all. (E25BMH 61RK L 1037162 G)

The engine will randomly destroy its spark plugs. When I say destroy, I do not mean any physical damage, the spark plug itself looks like brand new with a little bit of signs of usage. There is zero physical damage to the firing tip, insulator or any other part of the spark plug. The gap has not changed at all either.

The spark plug will however not create a spark anymore, neither in the cylinder in which this occurred, nor if I swap it to a different cylinder. Both of the cylinders will show this behavior randomly after 5 - 20 hours but not at the same time. The plugs are not shortened when I test them with a Multimeter nor can I find any other apparent reason for them not working anymore.

Putting a new plug in remedies the issue straight away and it will run perfectly for another 5 - 20 hours on that cylinder. This surely is not just bad luck as we have chewed through around 12 plugs in the last few month now. The plugs we are using are BR7HS-10, which according to my manual should be the correct type and as we have used these types of plugs for the last years I doubt there is something wrong with the plugs.

What I have done so far to remedy the issue (Mainly because I had some parts from another engine around that I could use):

1. Changed the ECU
2. Changed the coils and their spark plug wires
3. Checked the cylinder head for any physical damage - Nothing found at all

The last thing I could think of is that the engine for whatever reason creates a very low ignition voltage and as soon as the resistance increases slightly in the spark plugs no spark occurs anymore. How would I go from here to check the ignition voltage? I would rule out bad coils, as I have 4 different ones and the problems occurs on every single coil.

Any help or pointers into the right direction are much appreciated.

Thanks in advance

Thomas