Warning, esoteric techno-babble content-
This is an EMI (electro-magnetic-interference) problem.
The electrical noise from the ignition system is being
picked up by the timing light. There are two possible
coupling modes for these type problems, radiated & conducted.
Your's sounds like the latter, although sometimes both
modes play a part.
It sounds like there might be some impedance (resistance
at RF) in some of your electrical connections. This usually
cannot be detected with a standard Volt-Ohm meter. To isolate
the problem(s), try this:
The light works fine when powered & grounded at the battery so
try moving just one lead to the next node (junction) in the path.
i.e. try moving the timing light power lead to the other end of the
battery cable (at the starter solenoid or battery cut-off switch).
Or try moving the timing light ground to the point where the
battery ground connects to the engine. Both of these tests should
not cause the timing light to flash incorrectly. If all is good,
move the timing light connection to the next node "down the line".
If the timing light malfunctions when grounded to the car body or
attached device, check &/or repair/replace the body ground cable.
The other possible player is a radiated coupling mode:
It might be the timing light power/ground leads are
acting a little like an antenna and picking up the radiated
noise from the ignition system. I'm assuming this is pretty much
an "unsuppressed" ignition system which can generate a good deal
of RFI. When the timing light is flashing (and shouldn't be),
try adjusting the "lay" of the cables. Move them around. Put
as much distance between them and the ignition wires as you can.
If they must touch, try to make them cross at right angles.
If this seems to make a difference, try putting a lot of twists
in the power/ground pair. This will decrease pickup of differential
mode noise.
All of this is academic as you already know how to make the light
work properly. However locating & eliminating a high impedance
junction in your electrical/ignition system might help the car to
run better. I certainly can't hurt ;-)
Hope this helps,
-Bob
Matthews, M D (Matt) wrote:
> I'm pretty well stumped.
> [...]
> 2) I get the same abundant flashes with or without the sensor being
> connected when I use an engine ground and power directly from the
> battery, or connect the timing light ground to the negative pole of the
> battery and pick up the hot lead from the engine compartment. In both
> cases 1 and 2 I get the same pattern of flashes with and without the
> sensor and with the sensor on any high voltage wire, plug or coil.
>
> 3) However, if I connect both the power leads to the timing light
> directly to battery I get no flashes until I put the sensor on a plug
> wire and then I only get flashes where they belong, no extras. On time
> for plug one and rotated appropriately for the other plugs.
[...]
> I consider this to be bizarre. It may not really effect the plugs firing
> ( see observation 3 ) but it seems as though the ignition is causing
> some sort of power fluctuation in the 12 volt system of the car and that
> the battery can damp it out. However, the car does not seem to run quite
> as crisply as I would like and the power fluctuations in the 12 volt
> system can't be helping matters.
>
> Any suggestions.
--
Bob Sykes
"You can't beat your brains for entertainment."
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