[Healeys] Car dies suddenly
michael.oritt at gmail.com
Tue Mar 19 11:45:44 MDT 2019
Yesterday morning I went out for a drive and after about five miles the car
suddenly died. There was no rough running, sputtering or missing leading up
to it—the car simply died. I coasted to the side of the road and after
about 30 seconds since the key was still on I pushed the start button. To
my surprise the car started immediately, revved freely and idled smoothly.
A bit perplexed I decided to drive on to see what would happen now that I
was paying close attention. The car accelerated smoothly and ran fine for
about 1/2 mile and then it died again in the same manner as earlier. I shut
off the key, popped the hood and examined the ignition system. Everything
seemed fine—all spark plug leads were firmly in place as was the lead from
the coil to the distributor. The power wires to the coil were tight and the
harness/connector to the distributor (see below) seemed fine.
After scratching my head for a couple of minutes I got in the car, turned
on the ignition and pushed the start button. Again, the car started right
up and ran normally. With fingers crossed I headed for my shop/garage,
about ten miles away and got there without any further event. Though the
problem did not seem to be fuel related I decided to verify that this was
not a fuel delivery issue. I have a double-headed SU fuel pump wired to a
switch mounted just behind the driver’s seat which allows me to switch
between pumps as well as turn the fuel pump off. While I was running the
car at highway speeds it ran perfectly on either pump and when I selected
the “off” position it slowly lost power as I expected it to—but in no way
like it had suddenly twice died 15 or so minutes earlier. This indicated I
was not dealing with a fuel issue but rather something related either to
the ignition system or to the primary wires that run to it.
This morning I dove a bit deeper to try and diagnose the problem. The car
has a Mallory Unilite ignition system tied to an MSD coil which has been in
place and performed faultlessly for a number of years. I removed the
distributor cap and everything appears to be okay, at least visually. The
interior of the distributor was clean and dry as was the cap, leads, carbon
contact, optical reader, etc. Mallory specifies the use of a ballast
resistor in the lead from the power source to the coil and with the engine
fast-idling I tested 12.5 VDC to the resistor and about 5.5-6 VDC out of it
and at the positive coil terminal.
I have a large low-oil pressure light that is mounted in the dash in place
of the original overdrive switch. It is wired from the ignition switch
through a 10 psi normally-closed switch mounted in the oil pressure gauge
sender line and then to the light. I point this out because both times when
the engine shut down yesterday the light immediately came on, from which I
conclude that the ignition switch itself is not the source of the problem.
And though I did not remove the ignition key switch the wires to and from
it seem tight and intact.
So my question is: What do I do? I hate to throw parts at it without
finding something that appears to be defective but I don’t know where to
start any further tests, etc. I also don’t want to simply wait for the
issue to happen again. BTW over the weekend I drove about 150 miles with no
issues whatever. Beyond installing four new plugs last week I have not
performed any work related to the ignition system. All
Best--Michael Oritt, BN1
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