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MG TD TF 1500 - COIL FAILURE
|Engine quit on the road,. It first stumbled then a few blocks later just died. fuel pump working & fuel in the carbs. it just would not start. Once home and about an hour later I went to check the ignition HT wires using my timing light and it fired right up.|
The coil is relatively new. I checked the resistance between the + & - posts. The resistance reading would initially begin at about 0.1 ohms and slowly rise to 3.4 steady then rise to 4 .6 and once to 7.1. If I held the meter leads on long enough the reading would subside to 3.6 ohms. I have an old lucas coil and the resistance behaved much the same slowly rising to about 3.1 but not continuing higher.
The point gap was OK & the points looked fine. All the dizzy internal wiring is good, no shorting. I have replaced the condenser but wonder if I need to replace the coil.
Advice and comments welcome.
|M E WADDS|
This sounds like a rotor arm problem, I had two fail in the way you describe.
As suggested check rotor - if it's one with a rivet to hold brass contact throw it away, once you've found a new one! Original Lucas had no rivet, just a moulding to hold the contact. Plenty of second hand ones over here, but if you cant find an old one look in Archives where reference is made to a good modern replica now being made without a rivet!
Simplest way to check the coil is to sub with a known good one. Coils will often fail once they are warm - the windings are breaking down inside. Beware, many modern coils are very poor quality, and sourced from goodness know where. Ignore the name on the box, speak to friends etc re a reliable brand!
Good luck, John
|J C Mitchell|
|This sounds exactly like when my coil failed. It would run fine for a few miles and would die and would not restart. I'd push the car home, wait a few hours and it would start quickly, run fine and the cycle would repeat itself! I replaced the rotor, cap, wires, plugs, and condenser. When this didn't help, I checked the fuel pump and carbs. When I finally replaced the coil, the problem went away-never to return! I would suggest, perhaps, borrowing a coil that you know is good. Everyone tells me that there are alot of bad ones around from third world countries, but I have to say that the generic coil that I bought form Moss for $16.00 (10 years ago) has been fine.|
|This is becoming a more common problem with Lucas and other oil filled coils. The windings are breaking, causing a change in resistance as it heats and expands. Get a new coil and hoefully your problem will be solved. Any 3 Ohm internally ballasted coil will do. I prefer the Bosch Blue coils or the pertronix (black) epoxy filled coil #40611.|
Jeff Schlemmer should know, bearing in mind the work he does on ignition systems. I forgot to mention that I'm also so distrustful of 'modern' coil reliability I use older second hand genuine Lucas coils from the 60s&70s that were well made in the UK and last for many years.
When I acquired my TF a few years ago it still had the original Lucas coil of 1954!- although it finally failed around a year later, exhibiting similiar symptoms to yours!
|J C Mitchell|
|Thanks to everyone for the information and advice. I am replacing the condenser, points, rotor and coil.|
The points appear OK so they will become a spare. The resistance in the coil varies every time I test. Using a digital ohm meter, the reading rises slowly to 3.4 ohms then keeps on going to 5+ or even 7+ then settles back down to 3.5 to 3.9 ohms. The coil was bought from my local auto parts store so I assume it was built for a N.A. car with the correct resistance. The coil has about 3000 miles on it. The condenser about 2000 miles as my first one abandoned me in the middle of a busy intersection. My distributor was built by Jeff Schlemmer three years ago. I will purchase the pertronix coil.
|M E WADDS|
This thread was discussed between 17/02/2009 and 22/02/2009
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