At 09:33 AM 6/4/2000 -0500, Kevin Brown wrote:
>....
>.... TF 1500 .... started to miss and died. .... plenty of gas .... power
to the distributor and coil. The points were opening and closing fine ....
no spark at all, even if I stuck a screwdriver right in to the coil. ....
Sometimes I would have spark and the car would run fine for a few seconds
and then it would die and I would have no spark at all again.
>....
>.... I put the old coil wire and lucas sport coil (with a screw on
terminal) back in and replaced the loose connectors .... driving 55 mph
hour down the highway the car suddenly
.... again had now spark. ....
Intermittent no spark with known good coil = broken wire in the primary
circuit. Tough to diagnose when it's running. It helps if you can catch
the thing at a time when there is no spark. You have two possibilities, no
power from the ignition switch to the input side of the coil, or no
connection from the downhill side of the coil through the points to ground
on the engine block.
When you have no spark put a test light on the input side of the coil. If
no light the problem is in the supply wire between there and the ignition
switch. If it does light and still no spark the problem is between the
coil and the engine block.
Pull dizzy feed wire off of coil, connect test light to power at the fuse
block, probe dizzy input wire with test light, and turn the engine over
slowly. The test light should light when the points are closed and not
light when the points are open. If it stays lit when the points are open
you have a short in the circuit between the probe point and the contact
set, or at the contacts. If no light when the points are closed, start
probing sequentially farther down the circuit path until you do get a
light. The broken curcuit will be between the points of light and no light.
One common cause of intermitent ground through the dizzy is a broken ground
wire inside. There is a multi-stranded flexible wire underneath the
moveable breaker plate that grounds that plate to the housing of the dizzy.
After much flexing with each motion of the vacuum advance unit, this wire
WILL eventually break, usually near the terminal at one end, but sometimes
in the middle of the wire at the point of tightest bending. When it breaks
in the middle the outer insulation still holds it together, and small
movements will make or break the circuit depending on when the broken wire
ends are touching.
Similar intermitent contact can occur in the wire from the coil to the side
of the dizzy, or the wire inside from the side of the dizzy to the contact
set. Also check for intermittent contact at any wire connectors. You
could also have an intermittent short to ground in the circuit between the
coil and the contact set. The test light is a master at finding these faults.
Good hunting.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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