Neglect or aftermarket: Which is worse?

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The Honda coil:
Where it is, what it looks like, and how to kill it...

You came from: Master List > Starting/Running problems > Bad coil

Update Feb/06: The original version of this page blamed the aftermarket plug wires for having insufficient resistance and causing cascading failures. I've been told this is incorrect. Apparently insufficient resistance does no harm to the ignition, but excessive resistance does. The coil failure documented herein was likely precipitated by the failure of the resistor in the aftermarket rotor.

Reader J. Poy's son has a 1991 Integra (a fine car, if I do say so myself). This sequence of photos was supplied by him, and was generated by him during his quest to resurrect this vehicle, which did not want to start.

To make a long story short for those not much interested (then why are you here?): What appears to have happened is that the son had installed a "high performance" aftermarket rotor, among other parts. The resistor inside the rotor failed. Once the resistor failed, current could not find a proper ground and destroyed the coil by grounding through its body.

Now the detail, and the photographs! (I love photos...)

This is a picture of the distributor with the cap off. The coil is at the very top, inside the distributor, still in place. Looks OK to the naked eye, but... And notice also the blue "cold air" intake tube. Looks cool, but did Poy's offspring know that the Integra already has a "cold air intake" from the factory? What else has the owner done to this poor baby?

Coil is removed, a simple job involving a few screws and a connector or two.

Now we can have a closer look inside. The yellow arrow is showing an area of burnt erosion where the cap's terminal would contact the coil's terminal. This erosion indicates a poor connection, which to me indicates an aftermarket or damaged distributor cap. Ordinarily this join does not flex, unlike in the old days, where you had an actual wire plugged into this terminal.

This coil gives a weak spark. There is no visible carbon tracking or other evidence of external grounding. (Here, from Mike Pardee, is another picture of a coil that has very obvious damage from internal arcing.)

Comparing the two coils side-by-side...

Rotor, still installed - arrow shows resistor

The bad rotor resistor was a surprise. Mr. Poy was doing diagnostics with a digital voltmeter when he discovered that the rotor had a potted resistor in it. He was previously unaware that the rotor even had such a thing. (The resistor might be an RF filter, I'm not sure.) The OEM rotors I've bought have all had black potting soil.

All other readings in the high-tension side checked out OK, except this resistor. It appears that when this resistor failed, the spark had nowhere to go, and so overheated and destroyed the coil.

Poy was able to restore the rotor to functionality by soldering in a wire jumper. Not the best solution, but probably OK for short-term use.

And here, the aftermarket wires. I can just make out the "Accel" logo on them. Maybe they are in fact very good wires. Maybe they do in fact allow a bigger or more reliable spark at the plugs (provided the coil can produce a bigger one). However, being aftermarket, there is a much greater chance of conductivity problems that would prevent the spark from dissipating its energy at the plugs.

Some questions regarding "upgrading" your ignition system with aftermarket parts:

How do you know you're actually getting a "better" spark?
In two words: You can't! You have no way of knowing, short of dyno-ing the car. As long as the existing spark is white to blue-white and is sufficient to start a healthy combustion process going in your engine, no amount of "upgrading" is going to give you more power or mileage. Either combustion occurs properly or it does not.

A "fatter" spark will not make any usable improvements in combustion efficiency compared to a stock system in good order. Unless you rework the combustion chamber shape, ignition timing curve, fuel delivery, cam profiles, exhaust backpressure...You get the picture.

A "fatter" spark may do nothing more than erode your spark plugs faster than they otherwise might.

Do you need a "better" spark?
Maybe. If you race, that is.

In some race situations, combustion chamber conditions are such that the spark can be quenched, and a beefed-up ignition system is necessary to ensure that the spark will not get drowned out. Racing engines with 14:1 compression ratios can fall victim to this. Your 10:1 road engine is unlikely ever to experience quenching, even at full-throttle and high revs.

If your spark is being quenched or weakened because your ignition system has been neglected, replacing only one component with something purporting to be "high performance" is not a good idea.

Well, aftermarket parts are a lot cheaper than that stuff the dealer tries to gouge me on, right?
Yes, until expensive stuff starts to fail (like coils). OEM parts are expensive for several reasons besides dealer markup. Firstly, they are tailored exactly to the rest of your engine's systems. Secondly, they generally fit a lot better than aftermarket, and last a lot longer. Thirdly, they are made to much higher standards than most aftermarket parts.

Think of it this way: Suppose you replace your cap, rotor, and wires every five years. Suppose you spend $200 each time to do it with OEM parts. Amortized over five years, that's $40 per year. And you'll have no trouble with them or their surrounding parts, either. Even if aftermarket is half the price, that's still $20 per year if you amortize it over five years, except that you're unlikely to get five years out of them...