I have a 2009 1.2 polo match (N9) If it starts it runs v.well but sometimes it just won't start it's had new spark plugs

and a coil no codes or errors are displayed no dash warning lights. Fuel pump working.

we checked earthing points and cleaned. we inspected connectors to ecu and found them to be clean.

On assembly we tried to start and it did. worked for a couple of days then not starting again.

It hasn't stopped working when the engine has been running and no symptoms when driving.

Any ideas and does anyone know where all the earthing points are.

Oh yes we did take all the plugs out and there was no spark so we think it must be some sort of electrical issue

So hoping somebody has had similar and maybe a solution

Thanks in anticipation Martin

Maybe possibly the battery - had the same issue on a Golf and just not enough current to turn the engine over and power the electronics - once started was fine

Also, check the crankshaft sensor and replace if necessary