Ignition/distributor cap/rotor arm question...

[simon a-b]

Hi, 

I have had an ignition fail. Driving happily along, good response, everything happy and well in the world. 

Then a couple of pops/stutters, a minute of more running, then dead. No spark at the plugs. 

 

I have a 9v coil, tested and good (checked resistance of both primary and secondary windings)

I don't have the resistant wire, I have a ballast resistor instead. Voltages checked- start circuit gets battery voltage (~13v), run circuit gets ~7v

I have lumenition. 

Bulb/pickup checked and operating. I did the test with a peice of thin carboard acting as the rotor vane thing cutting the beam. When I cut the beam I got a fat, healthy spark from the coil, down the main lead (arcing across to the cam cover to test). 

I have new spiral wound leads. 

Lumenition tested as well- bridging the blue and black wires at the three-pin connector also produces spark. Spark is good. So I don't think the 7v vs 9v is the issue- unless this is what changed, and I can't see how?

One question on the resistor- it's a ceramic block with a resistant wire protected by the ceramic. The wire glows red hot when it's running. The design holds it away from anything flammable so I think this is as standard, but I'd be interested if anyone thought this was a concern?

So the only conclusion I can come to is that the failure is somewhere between where the main lead enters the distributor cap and the plugs. No spark seen at any plug lead. 

Can a distributor cap or rotor arm fail like that? It seems to be the only answer.

The rotor arm is clean and good- I gave the end a light rub with fine grit sandpaper and the central button is clean. The pickups in the cap are clean too, I gave them a quick once-over as well. The cap looks to be undamaged. 

Will any Lucas 45D 4cylinder cap fit? Is there any difference between them? I've read of the blue cap vs the black cap- it's a S3 so no turbo. 

Thanks in advance (timing pun)

Simon

[drdoom]

Hey Simon,

I once had a comparable experience wherein my Elan engine cut suddenly during a road trip stranding me on a rural road a very long way from home. Could not readily figure what was the fault as all seemed mechanically in order, there was fuel in carbs and spark could be made to arc to earth from a pulled HT lead. In the end it was a fault in the rotor dielectric, barely showing a trace witness mark on the underside where it is perched on the distributor shaft where high voltage was shorting to earth via the shaft rather than across the plug gaps. A new rotor arm was the fix. Never had seen anything of the sort to that point, but I suspect this may be the nature of your problem. Keep us posted.

[910Esprit]

I believe blue caps (and rotor arms) were introduced for Lucas Constant Energy systems and allegedly have a higher resistance to electrical breakdown, however they are fully interchangeable with black versions.   I also suspect your rotor arm, which definitely can go bad, but visually look OK. 

[jonwat]

5 hours ago, simon a-b said:

One question on the resistor- it's a ceramic block with a resistant wire protected by the ceramic. The wire glows red hot when it's running. The design holds it away from anything flammable so I think this is as standard, but I'd be interested if anyone thought this was a concern?

Never heard of that before but I wouldn't want a red hot wire sitting directly under my carbs 

[Sparky]

+1 for rotor.  And the obvious silly question but you never know: is the shaft turning?

[fjmuurling]

A red hot resistorwire is not good ( except in heaters). 

I would check the current through the resistor, and measure the voltage across the resistor and the at the coil. If they are right then the wattage of the resistor is too low. If not then somethings else is not right

[CarBuff]

There are reports of the riveted dizzy rotor causing no spark situations.

And of course, the wire to the pickup inside the distributor often can break, where it flexes during advance/retard.

Finally, we had that same pickup wire break (inside the insulation) right at the plug/jack where it connected to the car wiring. (from shaking around during driving)

[drdoom]

No good in that ballast wire running red hot, clearly. I believe one may delete the ballast running Lumenition as long as the coil is a suitable match which seems not to be in this case. Red hot wire = excessive amperage.

[ekwan]

If the ballast wire / resistor is running hot, it means that there is an internal short in the coil.

[CarBuff]

8 hours ago, ekwan said:

If the ballast wire / resistor is running hot, it means that there is an internal short in the coil.

OR, its the wrong resistance coil.

 

FWIW, some ignition system providers (Pertronix?) specified coils of a different resistance than stock. Then, if they failed and 'factory' parts were refitted, you could see the issues you are experiencing.

[ekwan]

Lumenition do specify coil resistance for their different systems 

[simon a-b]

Thanks for all the input. Rotor arm is a good option to check, and that the shaft is even rotating! 

I'll be away from the car for  a while but will get a replacement cap and rotor for when I get to try it. 

Ballast resistor is nowhere near the carbs- my car has a separate fibreglass box for the ignition parts which bolts to the side of the engine bay, up against the boot wall so it's quite protected. 

When the resistor is in circuit I'm getting 7v at the coil, and good spark so would that rule out an internal short in the coil? It tested in the right range for resistance. It definitely needs ballast, it's marked 9v on the coil. 

I'll update when I can get back to the car...

Simon