Replaced knock sensor, cleaned out radiator

Lesson for today: in a small-block chevy,

THE KNOCK SENSOR IS REALLY A COOLANT DRAIN PLUG. 

For fuck's sakes. I don't think there's any technical reason it should be connected to the coolant passage.  The wisdom at thirdgen.org suggests GM simply cheaped out and re-used an existing drain plug for the knock sensor.

GM's shop service manual, chapter 6E2-C5-1 - "Electronic Spark Control (ESC) System" does not mention anything about this. For the benefit of future generations, there should be a step 3.5 under Remove or Disconnect, namely "Prepare to swim in coolant". At least the stuff wasn't hot anymore.

Anyway, there's now a new knock sensor. Apart from some wiring harnesses, all ignition parts are new/replaced.

Since most of the coolant ended up on the driveway, I had an opportunity to flush the radiator, coolant reservoir etc as well. This actually came at a good time - there was a hideous amount of sludge in the system. Apparently I had messed up the coolant/water ratio last year as well -- the liquid had frozen during the winter and now coolant was seeping through the water pump gaskets. The pump will be cleaned and new gaskets installed, if I can manage to pull that thing out.

ESC module changed; Isolating the ignition problem

I've replaced the ESC module. Now almost the whole ignition system is new - except for the knock sensor and some wiring - yet the same problem persists. Here's a another home video showing the problem.

However, I've managed to narrow it down. If the EST bypass (aka set timing) connector is open, the engine runs just fine! The ECM sets error code 42 and the SES light comes on, as should happen when the connector is open.

So, the problem is somehow related to how the ECM controls spark timing.

Last time, I had set the spark advance to "apparently 0", like this:

In this position, when the bypass cable is disconnected, the engine sputters a bit and feels like it's hesitating on idle. So I rotated the distributor until the idle sounded smooth and stable - the timing is now on the last tooth:

             ___________
            /           |
            \___________|
                 v v V V   O
                 |
                 |
                here

I haven't seen _any_ of the tachometer flip-outs, stalling, sputtering etc when driving like this. The power - what little the stock TBI has - is mostly present too.