At 05:01 PM 9/13/2008 -0700, David Breneman wrote:
>.... got about 200 feet up the driveway and the engine just
>died. .... like you'd turned off the key. No spark.
Good start. That narrows it down to an ignition problem.
>I'm suspecting it's the coil because there is no spark when you
>separate the points (indicating a shorted condenser, yes?),
Maybe. It is unusual for a condenser to short out instantly. When
it was working, a condenser will usually go from bad to worse in 10
minutes or so, getting to the point where it has no power and
backfires so bad you cannot drive it. But usually not instantly dead.
>there is pulsed 12V going into the low-voltage winding,
If it is pulsing that means the points are opening and closing, and
the condenser is not shorted out. It also means there is a complete
circuit through the primary winding of the coil, not open circuit.
>and nothing coming out of the high voltage winding.
(No spark).
>The high voltage side reads 9K Ohms
Close enough.
>and the low voltage side reads dead short.
Not good. Primary winding should measure about 3.2 ohms (or a little
lower for a high energy coil). You need a low resistance range on
the ohm meter to measure this. Disconnect wire(s) on one of the
primary terminals and measure resistance again. If it is dead short
(0 ohms), the coil is toast.
>Is it common for a coil to just "up and die" this way with no
>warning? It's a Lucas DLB-101. ....
>....
Not so likely, but possible. Coils also usually fail in a progresive
mode, producing progressively weaker spark until it won't run. A
failing coil will commonly be temperature sensitive, failing when hot
but possibly recovering when cool.
Review trouble shoting here: http://mgaguru.com/mgtech/ignition/ig106.htm
Testing coil here: http://mgaguru.com/mgtech/ignition/ig108.htm
With good condenser you should get 1/4-inch blue spark in open air.
With bad condenser (open circuit) you might get 1/32-inch orange spark.
Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com
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