LUPO 1.0l MPI Misfire Cyl2

[ademason]

Please can anyone help.
My Missus 1ltr MPI LUPO has developed a MISFIRE.
VAGCOM reports Cyl2 misfire, however, when I unplug Cyl2 HT lead I also get rouger running and Cyl3 misfire also flags! Likewise, if I unplug Cyl3, iget both Cyl2 & Cyl3 reported as Misfire.

Any ideas? I don't suspect plugs or leads.

VAGCOM LOG
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 - -
16686 - Cylinder 2 Misfire Detected
P0302 - 35-00 - -
Regards,
Ade

[MasterMickVW]

I'm pretty sure these work on wasted spark ie u have a twin coil 1 half does 2&4 and the other 1&3 i think.I would double check the leads esp No'4.And for the sake of a couple of minutes work check the plugs.V easy to get carried away and miss out the basics.

[ademason]

Thanks. You're correct. It's wasted spark.

Yup, I took the engine cover off this eve and removed plugs and leads.
Plugs needed replacing anyway, but it was the lead to Cyl2 that had failed (confirmed by moving it to a plug on the other coil)

Even though the lead has failed in some way, it must be shorting to ground and providing the path back for cyl3, because it still needs to be connected to cyl2 to ensue cyl3 fires. If you remove the lead from Cyl2 (even though it's faulty), cyl3 also fails due to no path through cyl2/3 coil on this wasted spark system.

How do leads typically fail?

[MasterMickVW]

Normally fail thru insulation breakin down in lead poss thru heat or the other cause is when leads are pull off with long nose pliers etc they get damaged.