Coil pack melting

StephenG · Post by **StephenG** » 30 Dec 2020, 06:23

My 2004 c70 2.4t started to misfire a few days ago. I found the no4 coil pack burnt out so replaced it with a second hand spare which melted after about 6 miles. I replaced the coil pack loom which was showing signs of heat damage and tried a new coil which burnt out after running for only 2 minutes. I would not think a valve or head gasket could do that so quickly. Any ideas welcome

Post by **oragex** » 30 Dec 2020, 09:32

Pull the spark plugs and inspect. Make sure is the correct ones and a good brand. Also look closely at the wires to the plugs. There is also a ground cable in the back of the engine, belt side under the strut bar

StephenG · Post by **StephenG** » 31 Dec 2020, 04:04

Hi thanks for the feedback, checked all of the above when I rewired the loom all ok except no.4. plug isn’t firing, not surprising as the coil pack burnt out in 2 minutes. Hard to tell but it seems the hot spot is between connectors 3&4, the constantly live feed. If the ecu is not sending a pulse would that cause the problem?

Post by **abscate** » 31 Dec 2020, 04:20

The power supplied to the coils is very low, not enough to burn out the coils. I’m guessing the plug is loose or the head is cracked , letting hot gasses up and burning the coil

Another possibility is an electrical short in the loom but that would blow a fuse.

The coils always have 12 V supply, the ECU fires them by grounding them in this design

StephenG · Post by **StephenG** » 31 Dec 2020, 08:43

Not hot gases or a faulty plug, bearing in mind that cylinder doesn’t fire long enough to get hot before the coil pack melts. I think it’s an electrical fault, just been testing with a multi meter and found 7 ohms between the 12 volt feed and ground, this is on all coils as it’s a shared wire But haven’t found any cause yet, also it doesn’t seem to affect the other coils

StephenG · Post by **StephenG** » 31 Dec 2020, 08:50

Not hot gases or a faulty plug, bearing in mind that cylinder doesn’t fire long enough to get hot before the coil pack melts. I think it’s an electrical fault, just been testing with a multi meter and found 7 ohms between the 12 volt feed and ground, this is on all coils as it’s a shared wire But haven’t found any cause yet, also it doesn’t seem to affect the other coils. Also it destroys the coil pack without blowing the 15 amp fuse.

Post by **abscate** » 31 Dec 2020, 19:49

Is it physically melting or are just the electrical connectors melting ?

I’ve documented measured resistances somewhere in this Forum, I’ll search

Post by **RickHaleParker** » 01 Jan 2021, 02:35

Excess current causes excess heat. Check the #4 Spark plug for electrical defects. Shorts on the secondary side would not blow any fuses. The secondary is not active when the primary is. The primary circuit is open when the secondary is active.

StephenG · Post by **StephenG** » 01 Jan 2021, 10:10

Abscate; Hi, it’s the coil that melts, the heat seems to generate behind the connectors to ground and the adjacent coil connection (3and4 from memory)
RickHale Parker; Hi, I’m changing the plugs tomorrow for a new set, although swapping the existing ones did not change the problem to a different cylinder.

Post by **RickHaleParker** » 01 Jan 2021, 13:02

StephenG wrote: ↑01 Jan 2021, 10:10 Abscate; Hi, it’s the coil that melts, the heat seems to generate behind the connectors to ground and the adjacent coil connection (3and4 from memory)

Clean the bolt hole, bolt and the pad. It is also a ground. There are three grounds on each coil.