[Healeys] Austin Healey 100 Misfire Diagnosis.

[Bob Spidell]

Distributor cap shorting out.


On 9/28/2022 3:24 PM, Michael Salter 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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