Failing coil pack?

Maintenance/Repairs
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1

Hello folks,



I have a 97 Hyundai Elantra with lots of miles (well over 200kmi), but I still like to keep it going. I think the coil pack is failing. For several hundred miles, the gas mileage isn’t what it should be, and when I really step on it in a low gear the engine bucks a bit like its being starved for fuel. We’ve had some rain and on these wet days it runs rough and the engine is misfiring some of the time (blinking CEL). The resistance on the 3 terminals where the coil pack connects to the wiring harness reads around 0.4 ohms to no more than 1 or 2 ohms at any given point. I think it should be much higher so that leads me to suspect some of the windings are breaking down.



I will add that the plugs are new, and the wires are NAPA lifetimes replaced about 20-30kmi ago.



What do you think? I’m a little confused since someone told me coil packs don’t break down, they just stop working.

2

I am skeptical about any claims for “lifetime” plug wires. When it is dark, park the car in an area with no lights around and open the hood. Look for sparks and arcing around the plug wires and distributor cap.

You mention new plugs, and the wires; what about the distributor cap and rotor if the car has them? I don’t think this is a coil problem. The coil provides the power, getting the power from the coil to the plug creates the spark. Sometimes the wires cross and the power arcs from one wire to another and mistimes the spark in an adjacent cylinder, hence backfires and other symptoms.

Excessive moisture, dirt and dust make the sparking and arcing easier so if your problems are worse in the morning when there is a lot of dew and on days with a lot of moisture in the air that is a clue.

3

Here’s what Autozone’s online repair info says:

  1. Ensure the ignition is off.
  2. Perform a visual inspection of the coil pack. If it is cracked or leaking oil, the coil pack is defective and should be replaced.
  3. Disconnect the coil pack electrical harness.
  4. Label and disconnect the spark plug wires.
  5. Using an ohmmeter, measure the coil primary resistance between terminals 2-3 (coils for cylinders 1-4) and terminals 1-3 (coils for cylinders 2-3). Resistance should be 0.45-0.55 ohms.
  6. Measure the coil secondary resistance between the cylinder No. 1-No. 4 high tension terminals and the cylinder No. 2-No. 3 high tension terminals. Resistance should be 10.3-13.9 kilo-ohms.
  7. If resistance is not within specification or the test results in an open or shorted circuit, replace the coil pack.

There’s also a diagram there for the pin identification.

Don’t miss that the secondary coil resistance specs are kilo-ohms.

Even if it tests out ok, mist it with water & see if it does anything.

4

Its a distributorless ignition system with a coil pack.

5

This car has an ignition coil pack, no distributor or rotor. I’ll put it in the garage and see what I can see. I replaced the wires about 30kmi ago because I did notice arcing on one of the boots, though this engine has the plugs way down in these “wells” so its hard to see. I did pull off each plug wire with the engine running and it did run noticeably worse every time for each cylinder.

6 
[i]  coil packs don't break down[/i]

Anything made by man breaks down. I’d bet the first rock broke down within the first 30 days or three dinosaurs.

As for the plug wires, In my experience the best bet are OEM.  The fancy fat or colorful wires are really toys and not very good.  Cost and fancy looks do not mean good quality.
7

I don’t think the OP meant that coil packs don’t go bad - only that he’d been told that they either work or don’t work - that they go all at once. That part isn’t true though, to be sure. I’ve had to replace coil packs for exactly this kind of problem - performance becoming marginal. I’d also mention that these resistance tests did not indicate any problems.

There was also no mention of any weird or fancy wires. They’re just NAPA wires which are probably fine. I also don’t buy any kind of “lifetime” claim (though it is helpful to know that I’d get free replacements when they do go). I really doubt that these NAPA wires are bad after 30K tops. It is quite possible, however, if boot grease didn’t go on them, that there could be some corrosion.

I think the OP will likely end up with a new coil pack. They’re usually not that expensive and way easy to install.

8

OK. First, thanks for all of the replies. The resistance between the terminals reads 0.5 ohms, and 9.6 kilo-ohms between the high tension terminals. So the latter is a little out of spec. I don’t see any obvious arcing, nor does it get worse when I spritz the coil pack or wires with water (used a plant mister filled with water). I think since its a little out of spec, I’ll replace the coil pack unless there is something else I should check first.

Someone told me that coil packs either work or don’t work. I didn’t buy it either so I wanted to ask. Electrical components can fail outright, or they can “break down” and do weird things. Also, I always buy NAPA lifetime wires because if one fails I can get them replaced for free. I don’t care what color they come in, just as long as they work. I always use the boot grease that comes with a set.

9

The only other thing I would check would be the power supply to the coil. I don’t know what its supposed to get (Autozone might tell you that too), but its probably supposed to get a full 12V supply. Check that, wiggle wires, etc.