Expert: Roland Finston - 11/2/2009

Question
QUESTION: kills coils- New pick up coil new Dist. cap an rotor no fire out of coil after running  10 mintues

ANSWER: Hi Mike,
I believe the M-body is a RWD about which I don't have any manuals newer than '82. Which engine is in the car? Let me know and maybe that older manual will still be applicable. If so let me know and I'll take a look. The syndrome of running for a while, then loosing spark, then recovering after cooldown, is often related to a Hall effect sensor in the distributor which is wearing out, though maybe that is what you already replaced? Have you checked for 12v to present at the primary of the coil when you lose the spark. It should be there when you are cranking it. You could try jumping the ASD relay at that point and see perhaps if either the ASD is weak, or for some reason the signal from the pick-up coil is dropping out which open the ASD for safety reasons.
Roland

---------- FOLLOW-UP ----------

QUESTION: 318 two barl & RWD. coil not recoving every time after cool down, it has killd 6 coils in 5 days. the coil is getting 12v when coil is good or bad its not that. the negative side of the coil is also hot, is that right?

Answer
Hi Mike,
It is an '83 manual actually and it shows that engine to have a 'spark control computer'. When you say that it 'killed 6 coils' do you mean that the primary winding has 'opened' (i.e. now shows infinite resistance?). If so then I wonder if the 1.2 ohm compensating resistor which is supposed to be in series with the primary coil is actually short circuited which would allow too much current to flow through the primary winding and burn it out. See if you can find that resistor in the wiring to the primary of the coil on the + side, and if you find it see what its resistance reads. That is about the only thing I can see which might explain such a coil breakdown. However, I am a total amateur with this particular spark system.
In answer to your question, the voltmeter may show 12v on both the + and the - post of the coil when the engine isn't being cranked. Once it is cranking the computer pulses the post which is what causes the spark, so I would not make anything of a static voltage reading.
There are several pages from the manual which I could xerox and postal mail you if you don't have anything to work with. It costs me 10cents per side to do that but you could send me back some postage stamps after you get the pages to cover the costs.
If you can get it to an auto electric shop with some old-timers who know the system they might be able to figure out quickly.
But check out to see if you have a shorted resistor.
Roland