1.4 16V Petrol BKY Auto Crank But No Start / Starting - Solved

I have just had a character building experience with my Polo 1.4 16V Auto with a petrol BKY engine, I know it is not a Skoda but is a close cousin and I’ve found this forum handy in the past. (So I write Seat / Skoda / VW in the text to enable a search to catch this).

I am posting it as it may help someone else and to make it searchable so others may be helped.

Situation is that it was being used and just would not start, not a specially cold day. It has done this twice before and mysteriously springs back into life. This time it took 2.5 weeks to get going this time. This is what happened.

I know that to get an engine going you need : spark + fuel + cam timing + etc.

1.    When I sprayed Easy Start down the throttle body it did not start. As Easy Start replaces the petrol this ruled out a fuel issue.
2.    The cam timing was easily checked by pulling off the cam cover and observing the movement of the cams and their markings whilst a long screwdriver was being pushed up and down by poking it down a spark plug hole (which on this engine is vertically above and inline with the piston stroke). I used a spanner on the big cam wheel nut to turn the engine gently.
3.    I pulled a coil out and put a spark plug in the end, then using a large crocodile clip grounded the thread of the spark plug. When I cranked the engine there was a yellow/orange spark. An internet evening told me that yellow/orange is a weak spark which can be quenched by fuel and a blue spark is required. So I’m loosing voltage somewhere.
4.    I got 4 second hand coils. Put them in – no difference.
5.    Cleaned all the earthing points that I could find, there are a few. – no difference.
6.    I tested a coil on the engine as before – no spark at all.
7.    I figured out the coil wiring on the car (which is not like I found on the internet) There are 4 wires. Starting at the square end of the connector

1. a.    Brown – Ground
2. b.    Brown / Yellow – Gound locally on the cam cover.
3. c.    Purple – Ignition permanent positive.
4. d.    Thin coloured wire – Pulse from the ECU to trigger the coil and hence the spark.

8.    I tested a coil pack on the bench by connecting the first 3 wires to a battery, grounding the spark plug using the croc clip. When I dabbed the pulse wire onto the battery a nice blue spark. So at least one coil is good.
9.    Then I changed all sorts thinking the ECU was not working or getting a signal from a sensor.
10.    I had observed on VCDS that the crank speed was about 200 RPM using the crank sensor.
11.    Finally the battery was charged for many hours and after cranking and then full throttle and cranking (which stops fuel injection and thus dries the engine a little) it spluttered into life and has not looked back.
12.    CONCLUSION – THE BATTERY WAS LOW. It now cranks a lot quicker and starts easily.

I hope that this helps someone as there are a lot of cranking and no start posts out there.

RRegards,   John