[Healeys] Austin Healey 100 Misfire Diagnosis.

[Bob Spidell]

re: "... I don’t recall if that wire is separate from the distributor 
wire ..."

It is (or should be). If the battery switch is in the 'OFF' position it 
grounds the coil primary so no spark.


On 9/28/2022 8:34 PM, Alan Seigrist wrote:
> Hi Michael -
>
> Have you tried cycling the connections on the white wire from the 
> ignition switch to the coil, and also from the coil to the distributor.
>
> You might also want to try disconnecting the black and white wire at 
> the coil from the battery master switch - if it’s failing you’ll get 
> weird symptoms like this.  If that wire is disconnected the car should 
> run no problem.  I don’t recall if that wire is separate from the 
> distributor wire, if it isn’t you’ll have to disconnect it from 
> underneath the master switch itself.
>
> Best,
>
> Alan
>
> On Thu, 29 Sep 2022 at 6:47 AM Michael Salter 
> <michaelsalter at gmail.com> wrote:
>
>     **
>
>     This problem has plagued me for over 1000 miles.
>
>     Today I had to drive some 200 miles and this is how it went:
>
>     Starting from cold I experienced a persistent and irregular misfire.
>
>     Pulling the choke out made no perceivable difference.
>
>     Power was not much affected and the car cruised along well in top
>     overdrive with just regular periods of misfiring.
>
>     Climbing slopes really made no difference, even when full throttle
>     was applied for 10 - 15 seconds.
>
>     Misfire continued for some 90 miles with no change when the engine
>     was fully heated up.
>
>     I could really do nothing to influence the rate of the misfire
>     although it did seem to be slightly less evident at low throttle
>     settings.
>
>     After 90 miles I stopped briefly to get fuel and upon starting off
>     it was quite evident that the misfire had disappeared almost
>     completely and remained that way for at least 80 miles after which
>     it started to misfire just a little as I came to the end of the trip.
>
>     _POSSIBLE CAUSES_
>
>     1.Plugs … not like a bad plug. The misfire seems to be more than 1
>     cylinder and never came close to being the regular beat that 1
>     plug misfiring produces. All the plugs have a healthy brown/ grey
>     appearance.
>
>     2.Coil …In my experience coils are very reliable but when they do
>     fail they tend to fail as they warm up and the problem gets worse
>     as the coil warms up
>
>     3.Points … a possibility but the dwell is set at exactly 60
>     degrees and does not waver at all when the engine is running in
>     the shop.
>
>     4.Fuel pump … if the engine was starving for fuel because of a
>     fuel supply issue caused by a blockage or failing pump the problem
>     would get worse when the demand for fuel increased, as in climbing
>     a hill of full throttle. This was absolutely not the case.
>
>
>     Any ideas folks?
>
>
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