[Healeys] Austin Healey 100 Misfire Diagnosis.

Roger Grace roggrace at telus.net
Wed Sep 28 17:02:06 MDT 2022

The real mystery is why did it stop after you refuelled ?
Was there enough time for something hot to cool down - but that does not
really explain theinitial missing when cold.
Presume that you have given the cap and rotor a good visual ... tracking
can have weird effects.
Plug leads ?

On Wed, Sep 28, 2022 at 3:46 PM Michael Salter <michaelsalter at gmail.com>

> 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.
> 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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