Diagnostic consult needed: Can a shorted/failed coilpack take out the upstream fuse?

So in today's cave of bad ideas, I bought a 500$ B6 A4 quattro wagon, 1.8t, that likely needs a head gasket. 

Like all VAG cars from that time, it of course needs some other items. 

After driving it around the block, the coilpack harness let its smoke out while idling in the garage. Okay, so that's common on these, and they make a repair harness. It popped the engine management fuse, so that did its job. 

Install the repair harness, go to fire it up, fuse pops again. Figure I must have screwed up when I made the connections. Checked, all good. 

So then I started digging deeper into the harness and I'm getting some funny multimeter results, so I test the replacement harness connected to the coils but not back into the factory harness that goes to the car. 

Okay so maybe the replacement harness is built wrong. Remove from the car completely, test all connections and circuits, all check out good. 

So I start to review the ignition coils, and well, there is definitely a problem. 

I've never seen a coilpack fail this way before, but there are two showing a short between the power and ground and are (I'm assuming) causing the fuse to pop. 

I'm wondering if the original harness that gets crispy from the exhaust and failed took two coils with it. Obviously they are sealed units, so there is no fixing them, and I have some coils on the way, but this all makes sense, right? 

I have no idea how long the original harness has been slowly failing, so in theory, the coils could have been putting up the good fight for a while and then the guts just had enough and melted their innards together. 

Just seems odd to me that any instance of a failed coilpack would cause a complete engine shutdown. 

It can happen.  The most recent example I had was a Mercedes SUV with a V6, one of the coils shorted internally and took out the fuse that powered it and all sorts of other things.

Replaced the fuse with a buzzer, unplugged things on that circuit until the buzzer stopped buzzing.  Easy and made me look like a hero 

In your case, the coils failing is most likely what fried the wiring. The wiring is not anywhere near enough to the exhaust for it to come into play, heck some VWs in this era had plastic valve covers!

 Normally the fuse is supposed to blow to protect the wiring, maybe it had one of those high end Harbor Freight Nev-R-Blow fuses, or someone replaced the blown fuse with one of higher capacity.

Of course you'll want to replace ALL of the coils, preferably with VW/Bosch.

As an experiment, could you not harvest a coil  pigtail from the crispy harness, connect 12 volts to the 12 volt input of the coil and tap the ground wire against a ground to see what happens? Stick a plug in just for fun. I would put a fuse on the 12 volt side just to be safe.

Maybe those two are good and the others are all bad?

I've certainly had Ford era Volvo coils take out the fuse.

They are usually very stinky by the time they do that.  Probably lucky that they don't eat the driver in the ecu.

"... Just seems odd to me that any instance of a failed coilpack would cause a complete engine shutdown. ..."

All depends on what's powered off that circuit. If all the coil packs are powered in parallel from the one fuse, if one pack shorts, the fuse pops and removes power from all of them.

In reply to kb58 :

GM is nice in that they power the injectors and coils of a given bank from the same fuse.  You lose coils, you lose fuel, so you don't lose the catalytic converter on that side.

Okay guys, going to close this loop in case someone else needs the information. 

I had two shorted coil packs, which would immediately cook the EFI/Engine Management fuse on power up. 

Turns out, VAG 1.8t engines have a tendency to destroy their coil pack harness from exhaust heat. They turn into a brittle mess and short out on the valve cover or the other wires in the loom. My guess is the shorted harness took down the two coils with it. 

I installed a replacement harness, and new coils, all is well. 

Outwardly, the shorted coils showed no sign of failure, and they immediately failed, with no warning. They also make the car inoperable, which is an odd design. My hope would have been that a failed coil would cause a serious misfire, but not a total EFI shutdown. 

But, you know, I didn't design it so all I can do is take the information (and maybe a coil or two) on my next drive!

Normally coils fail to where the primary windings fail.  Your coils failed in a manner where the power transistor shorted, which is rare but possible.  No engine's going to run with a blown fuse.