Irritating Points Ignition Failiure - a bit stumped!

Is it a ballast coil?

From lead to earth, without a plug in? All six HT leads do the same?

Are the leads odd in any way, or could you beg/borrow/steal a single perfectly normal lead and eliminate them that way?

So the LT side, presumably, is fine - if the coil's giving a big fat spark. It's clearly somewhere on the HT side after the king lead.

You've replaced the cap & arm. So, really, that JUST leaves the HT leads... Odd that all six would do the same at the same time.

Hmm. I wonder... Could the distributor shaft have dropped somehow, causing the rotor arm to be making poor contact with the cap? Maybe some marker pen across the tip and the central contact, spin it over, and see if it's been removed (I'm thinking pikey engineer's blue...)

if the spark is able to reach the distributor cap, but gets no further then it is logical that either the cap or the rotor arm are faulty. even if one plug lead had died, the chances of 6 dying at the same time are nearly as slim as winning the lottery.

I would certainly agree and they've been replaced. Which makes it all the more frustrating!

No.

Yes for the coil lead, the plug leads I checked with plugs in.

Not checked.

They're pretty standard if bloody long. I'm not sure it's the leads as Mr Cheerful and you say the chance that all six fail at once is a bit slim.

Where would the shaft drop to?

That suggests the problem must be leads, rotor arm or cap. A lot of the reproduction stuff available new seems to be rubbish.

You can check normal resistive leads with a DVM set to measure resistance. They will give a reading of approx 2000 ohms per foot of length. One which is faulty will be very much higher than that. And check the king lead too. If they are the old carbon string type they do fail - newer decent ones made from conductive plastic seem to last the life of the car.

What about the carbon rod in the distributor cap - the one that can wear away unnoticed? Or the spring behind that can disappear? The ignition timing is correct and the rotor is actually turning? Yes? Advance retard weights/spring present and correct? Dave

They're all there.

Rotor turns, is free on the springs (flicks back to its 'home' position) and the carbon brush is there and free.

I have no idea. I've never had a distributor out of an XK. BUT... I wonder if a bearing or a retainer or something allows slip, whether the gear at the other end could allow it to drop a few mm.

Hmm. Googling for an image shows that it's keyed at the bottom, so presumably supported. Still worth a couple of seconds to check, though?

It's definitely keyed - I'm tempted to try and get one from a breakers and see if a straight swap makes any difference.

There's Hove car Spares near me and he used to specialise in Jags and has a fair bit of the older stuff still kicking about - I managed to get a good rear hub assembly from him a few years ago.

critcher said................. replace plug leads and watch it fly.

Does seem very odd..

OK if you have fat sparks coming direct from the coil try a lump of ordinary wire, any old bit of cable will do, plugging that into a lead output direct from the distributor cap. See what the sparks look like holding that just away from an earthed bit on the engine block. If that looks the same then all OK in the distrib cap..

There will be a slight loss whilst the spark jumps from the rotor arm but it should be quite decent.

If its not then perhaps the rotor arm isn't for some reason where it ought be moved up or down check with a calliper gauge etc.

But what if its moved round somehow perhaps so the arm isn't matching the lead take off and that will screw up the timing very badly too as well as making the spark very poor..

So what's the reasoning?, this car just gave up on a motorway it wasn't as it had been getting very difficult to start over time or had piss poor performance so how do all leads fail at once or deteriorate so suddenly?.?..

Must be the coil then. Have you tried another good one?

I think I would take a punt on replacing the rotor arm *again*

The OP has said there's a good spark from the coil, but it's not getting to the plugs. I'm deeply suspicious of the dist cap. If it was OK, why was it changed a year ago? I would be checking it microscopically for tracking or cracking.

Steve

Two old ones and a brand new one. All three have same symptoms. Decent spark from king lead to earth.

I rebuilt the distributor and replaced the consumables (cap, rotor, points, condenser) as a service measure.

And looking it up, it was five years ago - it's had a couple of points and condensers since. I'll get another cap and try that.

I'll also dig out another king lead to try and see if there's some form of breakdown under load that's sending me up the garden path.

JAAMOI have you checked the dwell angle?

Another source of problems, that took me several days to find when my

HTH

Mike

I can't get it to run.

The low tension side seems fine as I get a spark at the coil.

So did the 105E, but there wasn't enough oomph to spark under compression. Your symptoms sounded to be very close to those I experienced, so thought it worth a mention. If you haven't tried a different plate, it might well be worth it!

Mike