Ignition coil meltdown

[MB TECH]

This is my first post on this board-
I have seen several ignition coils from a particular car maker that blister around the insulation and then the power stage or transistor inside burns up-these same cars also had a 600-900mv drop on the engine block main ground strap-I just can't wrap my head around what causes this. The case usially is 4-5 of six coils are bad. Even though the voltage drop is not directly connected to the coils could that be the cause. Looking at the control of these coils with a lab scope-I can see the drivers inside the controler are fine and so is the power and ground supply for the controler. I would think the driver circuits would fail first-but they check out just fine with new coils and repairing the engine ground strap.

[Lightages]

I don't think we have quite enough information. Is this occurring only one one particular car, or across many cars? Does this happen quickly or over a long period of time?

[trackman44]

Could you show pictures and maybe a circuit diagram? Sounds like the coils are being driven too hard. Plus are the coils OEM or after market?

Will

[Psi]

It could be the location where it's mounted. Maybe it getting hotter than expected with the engine running

[geo_leeman]

It could be the location where it's mounted. Maybe it getting hotter than expected with the engine running

That sounds likely depending on the exact configuration.  We used to have a similar problem on old tractors that the coils would heat up and fail... you could drive a ways, then it would quit.  After it cooled you were on your way again! 

[SeanB]

6 coils says it is either a V6 or a V12. adding extra ground cable to the block will help with current flowing through the coil LV wiring and overheating that, and you might complain to the manufacturers of the coils, likely Denso, Bosch or Magnetti Marelli in a lot of cases.

[Lightages]

It could be an inline 6 although I am not sure who makes an inline 6 anymore.

[deth502]

need more info. what type of vehicle, what type of engine, its configuration in the engine compartment, ect, ect....

you are absolutely sure that the only vehicles that exibit the voltage drop are the ones that are blowing coils?

first thought was, they all get a voltage drop, most sooner than later. connections get bad/oily, things corrode, fasteners loosen. it happens.

but if this is only on the problem engines, it may be that there is something in the coil packs shorting out the +v lead to the block somewhere, rasiing the potential of it, making it look like a drop if measured while running (therefore power ti the coils)

[SeanB]

Poor earth and alternator bolted to block means ground return will be via all other ground wires, like those for the knock sensor, crank and cam position sensors, plug modules and any other ground leads as well as poorly via the drivetrain. That will overheat wiring as these connections typically will not really handle 50A or so of current.Likely the plug modules have a 3 wire connection to have a ground for shielding the high current pulses to reduce RFI, and this shield current is overheating and burning out the internal potted wiring and warming up the connector. The ECU will have a large number of ground leads directly connected to the chassis so it will survive the currents with little problems.