Interesting Coil Conclusions

[David W.]

I have read on this board many times that ignition coils are either work properly or they go bad, which usually reveals itself by not being able to start the car. My '64 365 horse driver has been running fine very nicely since I bought it a year ago. It did have a very noticeable miss at about 4000 rpm if I got on it, which isn't very common. In any case, it had an aftermarket coil that had a 'special high output' sticker on it by some no-name company. It was not black so in my ongoing quest to get the engine compartment as stock looking as possible, I bought a proper black one from NAPA auto parts (based on comments on this board re good quality from NAPA). It made a very noticeable improvement in the performance and the miss completely disappeared.

So fellow tuners, don't overlook the coil even if the car starts proper and runs decent. I was surprised.

[Dick W.]

Re: Interesting Coil Conclusions

Coils can and will deteriorate resulting in poor performance. They are not necessarilary good or bad. There is a definite inbetween. Older Sun test equipment had a coil test option that you could observe the coil on an osciloscope and also test the windings with an ohmmeter.

[Dave S.]

Re: Interesting Coil Conclusions

David,

You have outlined why these coils must be run on a car where they are heated up and put under load. A continuity test will not identify a weak coil condition, just an inoperable coil.

[Chris H.]

Re: Interesting Coil Conclusions

I went through all sorts of coil gyrations with my 396. The motor would only take 1/2 throttle to redline. Turns out the previous owner had installed a non-TI (points) coil. After he sent me the TI coil he had yanked because it was "bad", I installed it and the motor ran full throttle to redline.

Of note, the points coil was operable with the modern TI amp (see above), but would not fire the original style amp.

[Mark #28455]

Re: Interesting Coil Conclusions

Also don't forget to consider your condenser (radio equipped cars). I had an original one go bad and the car just stopped (wouldn't run at all). When I disconnected the condenser, it ran fine again.
Mark

[Duke W.]

Re: Interesting Coil Conclusions

All point ignition systems have a "condeser" (actually a capacitor) in the distrubutor. It's purpose is to "absorb" the charge that causes current to continue to flow after the points open and subequent arcing.

Though they rarely fail, if they short, they will ground the coil and the ignition system will not function - as if the points will not open.

Duke

[Joe C.]

Re: Interesting Coil Conclusions

Duke:

I assume that Mark was talking about the radio interference suppression capacitor, attached to the positive side of the coil. He did, after all, say "radio equipped". If that unit shorts, it will cause a no start condition. I certainly HOPE that Mark understands that all points equipped cars will burn points in very short order, if run without the "cap" in the distributor.

Joe

[Duke W.]

Re: Interesting Coil Conclusions

It wasn't clear which one he was talking about, but if either capacitor shorts the ignition system will not function. The capacitor in the distributor probably leads a harsher life due to higher temperature. I've never experienced failure of either one.

Duke

[Joe C.]

Re: Interesting Coil Conclusions

Duke:

I had a points cap fail on my 1971 440 Challenger (OMIGOSH... please forgive me!!). Drove me crazy, because it was only a couple thou miles old, so I didn't go after it right away. I can still hear that MoPar hi-torque starter (dor.....tortortortor.......dor.......tortortortor tor.....)

Joe

[Duke W.]

Infant mortality

If you look at the failure rate of electronic devices it is relatively high for new parts, then drops to a very low level and finally rises at end of life, which for a capacitor can be very long.

In the aerospace industry we used to thermal cycle new parts and then 100 percent test them and some were "burned in" - electrically operated in test fixtures at elevated temperature. This was to shake out all the infant mortality cases, and if it was too high the entire lot was rejected.

These tests were for parts that were going into a geosynchronous communications satellite orbiting the earth at about 25K miles altitude, so any parts that failed were not repairable. The way to achieve high reliability was to ensure that all the parts were as good as possible and all systems had design redundancy so there were no single point failures that could put the system out of business.

Based on this experience I got out of the habit of changing the capacitor with every point change, but I always keep at least one "burned-in" (otherwise known as used) capacitor around just in case.

Duke

[Mark #28455]

Re: Interesting Coil Conclusions

Joe:
You're right. I was talking about the ignition noise suppression capacitor. My cars are all TI equipped and the reason I brought it up was that I too, like Duke, had never heard of one failing! I figured it out after replacing the TI amp and just wanted to let others know so they would replace the $3 part first.
Mark

[Craig S.]

Re: Infant mortality

We do the same on our higher end server and storage products at IBM....the electronic cards are thermal cycled in chambers under stress, and some of the components themselves are stressed at a chip test level before card assembly. Then we run them again a a box level assembly under stress before shipment. It really improves NDF (New Defective Failure) on subsystems. I always cringe when we install new service parts in the field.......you never know until they run for a while where you stand. Of course, none of this happens on the lower cost products such as laptops etc..... just the high end gear.......Craig

[Jack H.]

Burn-in was also intended to stablize....

the 'drift rate' of various components! In the good ole days, the construction of certain capacitors exhibited storage capacity change based on time/temperature. So, designs that required PRECISE filters, were 'burned in' to get the discrete components on the 'linear' portion of the lifecycle prior to final calibration/adjustment.

Some for the old school believe the more burn-in and stress that's done by the manufacturer is a token of quality. Sometimes yes, other times no. It depends on the specifics of the circuit topology and reason for the burn-in process. If a given design is NOT time/temperature dependent (eg. analog functions achieved via digital signal processing instead of discrete components), all you're doing beyond a simple go/no-go check is increasing mfgr cost and extracting useful life from the consumer....