she gave me a heart attack - Isolde had no pulse

A few days ago I loaded everything and ready to go into the city in Isolde. As I started the engine within a a couple of seconds the engine stalled out. No amount of cranking would restart it. I thought that is odd, as Isolde has been flawless in the last year. I immediately suspected it may be a problem with my home brew only-I-know immobilizer. I designed this immobilizer that is easy to use, impossible to find, simple and reliable.

I thought may be I was too sure of myself. I shelved this car trouble as I had so many other things on my plate. As it is a mystery and a symptom that is totally new for Isolde, I decided to sleep over the problem so I can have more time to ponder what the cause may be before tearing into her. I was very fortunately this happened in the garage before I pulled out. Had it occur on the road it would mean an expensive towing expense back to the ranch. I had diagnosed much more difficult problems before and the worst was an intermittent stalling which occurred far from home, and once I had to have her towed home.

Today with a clear mind I set out to troubleshoot the problem. The first thing to check is my handy job low tech immobilizer. That is all good. Next I checked the ECU master power relay and that too is good, and followed with the fuel pump relay also check good. All these checks with my new troubleshooting LED indicator like the old one based on a 12V bulb. Without it I would need an extra helping hand as someone has to crank the engine while the other person by the engine bay to witness the signals.

by taping it to this light fixture I can swivel it 180 degrees

it has been so long since I last consult this wiring diagram

next to be checked is the ignition spark

I made this ground clip planning to use it to ground the debugging spark plug but I ended up using a timing light instead

it took me a while to thought of using the inductive coupled timing light to check the presence of spark ignition; rather than using a test spark plug 

When I tried to verify the presence of ignition spark, I realized it would be safer and easier if I just us my magnetically trigger timing light. I put the center on the high tension cable between the ignition coil and the distributor. There was no ignition pulse. Now I suspect it may be the hall effect sensor inside the distributor. Although that seems unlikely as it is all solid state.

this photo found on the web is what the hall sensor looks like inside the distributor

Performing functional test on the hall sensor in theory is very simple and easy, however in practice it is challenging as there is no access to the signal, except one poke through the signal wire's insulation jacket to get to it. I didn't want to do that as that could lead to corrosion and intermittent failure down the road. A VW speciality shop would have a purpose made test device that mates to the distributor connector.

Without it I decided that pulling the ECU and solder on some test wires is my best option. Once the ECU is open I can also go on and check other signals should the hall sensor proves to be good.

I have open this ECU no less than 4 occasions

it has two PCBs

With each encounter of things that fail generally bring new anxiety and this time is no different. I was expecting to be a simple problem due to my not so well thought out DIY immobilizer but that turned out to be solid. As I suspect though don't think the hall sensor is likely to had failed, I brace for the worst. A quick check on the web this part is EOL, and the old stock are now $165 apiece. 

To date, my DIY servicing and troubleshooting of all the vehicles that I'd ever owned has been 100% successful. With each new challenges overcame made me stronger. I hope this event would not be an exception.