Stopped suddenly, seemingly no spark

T

typonaut

Member
I was happily driving my 2200SC yesterday, when the engine suddenly stopped. Ended-up having it recovered home.

Having looked at it now, it seems I have no spark (first check at the roadside was for fuel delivery, and that all seemed fine). There was no missfiring or anything, and no other problems previously - usually starts with a couple of engine turns.

I put an inline timing light on cylinder 1, and that showed no light on spinning over (I believe the timing light to work, but I could check again with an induction type timing light).

The coil has 1.6ohms on the LT side and 7730ohms on the HT side (I can't find specs, Haynes manual seems to be saying 3.5ohms on LT side), which seems to be in the ballpark for general expectations.

Power to positive side of coil is 12v, power out of negative side of coil is 1.25v. Checked continuity of negative coil wire to distributor, is ok, and 1.25v at that end too. Don't seem to be able to get a spark across points.

So, I am thinking it must be the points or the condenser - but never come across an example of either failing suddenly like that, usually you are getting some ongoing running problems first.
 
If you’re running points and condenser, and it’s a newer condenser l, you might find it has failed and is shorting out. The new condensers are notoriously unreliable and you may have experienced that.
 
Well, I put a new condenser on it, and that didn't seem to make a difference… but…

Looking at the coil again I noticed there was another wire on the negative side, so I took that off (as well as the one to the distributor), and then I had 12v on the negative side of the coil (previously I'd had only 1.25v). When I traced the "extra" wire I found that it went to an alarm. I've never used the alarm on this car, I'd always assumed that it was inactive, and was turned on/off by a locking switch on the rear panel (opposite side to the fuel filler).

So, I am thinking now that this is the cause of the sudden stop, perhaps there's some kind of immobiliser function that has cut in (though seems unlikely for an alarm that's around 50 years old). I reconnected the cable from the coil to the distributor, and had 12v at the distributor too. Couldn't test again, because I'd run the battery flat by this time – so will check in the morning, following a recharge.
 
Well, removing the alarm wire from the negative side of the coil saw the car start straight away. Tested this by putting the wire back on, and predictably it did not start. Really annoying that it took a couple of hours of faffing about to fix it, and no idea what triggered it.

BTW, if I were to fit electronic ignition, is the PerTronix the preferred solution? I had a PerTronix module on another car, and never had any trouble with it at all.
 
I’ve used both Petronix and Luminition’s magnetronic modules. I would say go for the more expensive Luminition system. It’s far better designed and I’ve never had one fail, unlike the Pertronix.

Lumenition Magnetronic Ignition System from Merlin Motorsport

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