Ignition fault finding

[Peter Naulls]

Some weeks ago whilst giving my neighbour a lift home from work in the special (he'll never ask again!) it developed a misfire at low revs, gradually worsening over the 20 mile journey. The next morning a quick check showed that the points gap had closed up to almost nothing. I reset it but the car wouldn't start. There is no spark at the plugs.

I've changed components one at a time, starting with the condenser (2 different ones), then coil, distributor cap and leads, points and rotor arm but still no spark. It is a 12v neg earth system and I am getting 12v at both of the low tension wires to the coil. With the ignition on if I flick open the points I get a spark across the points. All the replacement components were known to be working when I stashed them in the boot years ago.

What am I missing? could there be a short circuit in the distributor base plate? I know this should be basic schoolboy car maintenance but I'm stumped! Any ideas?

Peter.

[Colin Wilks]

"I stashed them in the boot years ago."
Condensers have a finite shelf life and don't like being bashed around. I would start with a new one.

[Peter Naulls]

Thanks Colin, I hadn't realised that. I have a brand new one in the Ruby so I shall try that tomorrow.

Peter.

[Colin Wilks]

Neither had I until I had a chat with Martin Jay at Distributor Doctor last year, when I was trying to sort my Series Land Rover.. He had had some new old stock OEM condensers, the majority of which turned out to be duff.

[Charles Levien]

Hello Peter,

Could this be the moment to consider electronic ignition?

Charles

[DavidB]

I now fit competition condensers from Swiftune. Originally designed for racing minis, they work a treat on our specials and I have never heard of one failing. 
David.

[andrew34ruby]

......and I am getting 12v at both of the low tension wires to the coil.

You should get 12v at both low tension connections to the coil -- when the points are open.

You could try replacing the coil with a bulb. With points open the bulb should not light. Points closed and it should light. Crank the engine and the bulb should flash.

[Peter Naulls]

Thank you David, presumably you mount it outside the casing as suggested on their site?

Charles, I wouldn't rule it out but at this stage I'd rather find the fault. First failure in 30000 miles so I can't really complain that it's been unreliable!

Andrew, I shall try the bulb trick - I was uneasy about both terminals being live and you've addressed that concern. I'll report back.

Peter.

[Duncan Grimmond]

As an aside, the bulb will give you a precise indicator as to the timing...

[Nick Mayne]

Have you checked the rotor arm? By the way should you change to electronic ignition with a Bosch distributor you may not get a spark at the plug but would from the ht lead. I found that the distributor rotor arm had a resistor buried in it in the black pitch like substance on the top. I dug this out and soldered a copper strip across and filled it again with molten pitch. All then worked fine with an excellent 1/2" spark when tested from the lead.