Is there any way to test a coil pack?

[Picasso]

I've been dealing with poor engine performance for months and discovered a bad coil pack a few days ago. It didn't fail completely and I never got a trouble code for misfires or anything else directly related to a bad coil. My engine has improved but still runs poor under certain conditions and I wonder if any more coil packs are in a state of partial failure. I'm getting a little tired of this continuous engine problem and don't want to resort to throwing parts at it in the hopes of finding the problem.

My question is this:
Is there any machine or device that an auto repair facility or dealership might have that can definitively test a coil pack?


Many thanks.


Paul

[Hi Volt]

Short answer, no. Testing can be done however it takes a setup beyond what a garage would justify having ( high voltage measurement, specified coil load device, rpm simulator, coil driver etc.). The closest you can come is a scope test while the coil is on the engine. This can zero in on the coil at fault, and then you have to determine whether it is actually the coil, the insulator boot ( most commonly neglected as people don't think they ever need replacing - WRONG ), spark plug wire ( V6 ) or spark plug. A cracked insulator on a spark plug ( sometimes hard to see ) can cause grief and eventually damage a coil insulator or plug wire boot. Since you are calling it a coil pack and not a coil I assume your have a V6? If so, the 3 plug wires are also a required maintainace item. A good place to get a full replacement set ( wires and coil insulators ) is Welcome to Sudden Impact Performance. They have a killer set for the 3.4L. If you have a 4.7L like me, there are coil insulators coming available. I have been waiting for a while now and I know a few others are as well. I talked to the sales dept today and they are long overdue ( new product coming ) but as soon as they are in my hands I will post as promised some time ago.

[v6er]

Actually you can test the resistance of the primary and secondary.

[Hi Volt]

Originally Posted by v6er

Actually you can test the resistance of the primary and secondary.

True, this is a test that one can perform and compare the results to the coil's resistance spec. But as far as a "definitive" test ( as was asked for ), the coil must be actively tested and put under load to test for proper output. This type of test will detect leakage which is the most common failure of a coil. Such leakage will result from a breach of the coil's body insulation allowing spark to jump to ground. Common place on new coil on plug style ignitions is also the insulator boot directly attached to the coil. Leakage in this area is too often diagnosed and treated as coil failure instead of replacing the insulators that is commonly the cure. An important thing to also remember is to replace the spark plug that was associated with the failed insulator as spark leakage can actually etch the porcelain insulator and thus carry the problem to the new insulator. This applies to ordinary spark plug wire insulators as well.

[Picasso]

I've got the 4.7 and recently replaced the plugs which made no change to the engine performance problems.

I replaced a second coil today which made another significant improvement. The first one replaced was for cylinder #8 with the second one for cylinder #4. The engine runs smoother, torque feels improved, and the exhaust is quieter. Having both on the same bank falls in line with how the engine felt and may explain the heavy vibration at highway speeds.

It feels like there is at least one more bad coil, so I'm going to do some more coil swapping to see if I can find it.

I wonder how far I'm going to have to take this. At $100 for a coil, this adds up quickly.


Paul

[Hi Volt]

Do yourself a big favor first, look at one of the "failed" coils and pinch the bottom seal that slips over the spark plug. Do you see any small cracks or slits in the seal ? Or are there any deposits on the inside of the seals that could be carbon tracking? These will vary in color but appear to be lines extending the inside length of the boot. Some of these deposits may be wiped clean, others are actually etching in the seal. I have extended the life of my seals by carefully wiping them and applying silicone di-electric grease to the insides of the seal. I plan to change mine out for new ones as soon as they arrive (patiently waiting, but first in line ! ). I have pushed my seals for over 300,000 Km when the normal life is 100,000 or so. The seals are not available at the dealer but I have found a source in the porcess of getting them, as mentioned before I will post when I get them.

[Picasso]

Originally Posted by Hi Volt

Do yourself a big favor first, look at one of the "failed" coils and pinch the bottom seal that slips over the spark plug. Do you see any small cracks or slits in the seal ? Or are there any deposits on the inside of the seals that could be carbon tracking? These will vary in color but appear to be lines extending the inside length of the boot. Some of these deposits may be wiped clean, others are actually etching in the seal. I have extended the life of my seals by carefully wiping them and applying silicone di-electric grease to the insides of the seal. I plan to change mine out for new ones as soon as they arrive (patiently waiting, but first in line ! ). I have pushed my seals for over 300,000 Km when the normal life is 100,000 or so. The seals are not available at the dealer but I have found a source in the porcess of getting them, as mentioned before I will post when I get them.

The boots on both looked almost new. I'll look carefully inside for what you mentioned and report back.

I had never heard of this boot problem. Having a rubber part act as a shield against a 50k volt spark doesn't pass my physics test. Not trying to be argumentative here, it just doesn't make sense to me. What am I missing here?

I do appreciate your help.


Paul

[Hi Volt]

The material used is actually an EPS (EPDM/silicone mix) rubber that has a fairly high di-electric strength. Also the coils actually only produce upwards of 30,000 volts on COP systems. On these coils, the spark plug insulator seats about an inch inside the coil (if memory serves correctly) so there is a distance factor to provide insulation against flashover, not just the boot itself. The problem exists when (as mentioned in earlier post) the boot gets a crack or a conductive path forms from contaminants inside the boot. The contaminants can be anything from residue passed onto the spark plug insulator from a dirty spark plug socket ( rubber insert inside socket should be cleaned regularily ) or from carbon that can come from leaking spark plugs. The carbon can either come from a loose plug or from a leaking seal between the metal base and the porcelain ( usually a band of brown will be visable ). The pressure from the leakage will blow the carbon right up inside the boot. Carbon being conductive will initate the tracking. A loose plug will usually deposit carbon on the exterior of the boot as well, while a leaky seal at the base of the porcelain insulator will usually deposit in the inside and very bottom of the boot. The same holds for spark plug wire boots, not just COP.

[Picasso]

I looked more closely at the inside of the removed coils and found nothing. They are clean and the boots have no signs of carbon or cracks.

At highway speeds I get a small but sharp vibration after replacing the coil over cylinder #4. I realized that the two new coils are next to each other in the firing order which makes me think that the other bad coil is over cylinder #3. I'm beginning to wonder if there is some other problem that makes it appear that the coils are bad when they aren't. The exhaust sound, torque, and fuel economy have all improved after replacing the coil over #4 though.

I still feel like Ferris Bueller's friend Cameron, that first morning that Ferris calls him.


Paul