At 04:50 PM 4/12/2011, Richard A Jones wrote:
>Hall sender on the distributor.

Anything at all in the ignition primary circuit, from the Hall sender
through the ECU to the coil itself and the +12 supply to the
coil.  The tach does a valuable service by telling you that it's
definitely an ignition primary problem, but beyond that you have to
track it down.  The Hall sender itself is a single transistor-like
component under very little electrical stress, not prone to
electrical failure.  I don't know whether as assembled in the
distributor it may have vibration issues - if the leads are soldered
that's always a weak point.  The ignition drivers are high-current
high-voltage high-stress components, and if they're in a
Digifant-type ECU they definitely are soldered as well, so they're
vulnerable in more than one way.

The distributor connector on WBX engines is a known weak point as it
disintegrates; as is the ignition driver inside the 2.1l Digifant ECU
(whereas the separate 1.9l ignition driver seems pretty bulletproof).

As I said in pmail, wiggling the wiring about while the engine is
running is a powerful tool for finding this kind of
probably-a-connection-problem.

Intermittents suck.  I spent fifteen years chasing a problem in our
gas boiler that would cause it to shut down and kill the pilot once
in a while on the coldest nights or when we were away.  Eventually
turned out to be bad solder on a control board.  Repair cost twenty
cents and about twenty hours of headscratching and monitoring temps
and such.  It only died seven or eight times total, never failed to
start up again; and only the once when I was tweaking and banging on
things...and I didn't understand the schematic as well as I thought I
did.  And of course there was a "red-herring" issue with a dirty
slide switch that confused me for a year or three.

And if you can't make the problem happen, the only way to be sure of
fixing it is to replace everything, wires and all.  When someone is
paying someone else for a repair, unless money is truly no object
typically nobody ends up happy unless the shop can replicate the
problem at will.  $$Time vs $$Parts vs $$Inconvenience vs
$$Reputation --> tears.  How it looks to me, anyway.

Yrs,
David