However what I hadn't yet mentioned was the awesome piece of troubleshooting that was performed last weekend.
When I bought the car, I neglected to mention that it had a steady miss at idle (obviously at idle, not like I was revving a car that had 16 month old gas in it)
Sunday after the rain started the only thing I could think to do was work on the engine in the cover of the garage, so I set at it.
First I wanted to identify which cylinder was out but it turns out with such a quiet engine that is already down a cylinder that can be a bit tricky. Certainly not as easy as it would be on a high strung 4 cyl like I was used to.
I pulled off each coil connector in turn, and I thought I could hear a difference on all of them. The number 3 cylinder did seem to make *less* of a difference, but it wasn't enough to convince myself. At this point I did a compression test which immediately ruled out a major mechanically problem as numbers came back 220-215-210-210-200 psi, so I put things back together with new plugs (no luck there, but they definitely needed changing anyway, that moisture you see is unburned fuel) and called it a day.
Then purely by chance later that day I was reading a thread about how an inline 6 is harmonically perfectly balanced, and how BMW likes to impress people by leaving glasses of water on the engine while it's running and being reved, and then some random forum goer happens to mention using the wave pattern on the surface of the water to track a difference in vibration caused by a miss.
Bingo.
It's really simple actually, i was a bit sad I didn't think of it myself first. Put a glass of water on a flat spot on the head, start the engine and observe the surface vibration (keep in mind I was already down a cylinder. Tested on a perfectly running I6 engine that was there helping, the water is nearly still)Then simply unplug each coil in turn, watching for a change in the water. If it doesn't change, there is your dead hole. Turns out my ear was right and it was #3.
So, I was excited that I could now simply replace the coils and have a mechanically beautiful engine.
But wait, it got even better.
The next day I went back out to the car to remove the alternator (it needed replacement) and had some time to kill so I figured, why not check the coil plug boot? I didn't expect anything, but hey who will it hurt.
So I pulled the 1 and 3 coils, swapped the boots and started her up.
The misfire followed the boot!
So in the end I Tracked down a misfire that turned out to be just a fricking coil plug boot. How awesome is that, I got a stonkin deal on the price because when it ran it had a steady miss. I actually bought it believing 100% that it would need a rebuild.
Turns out all it needs is a 6.47$ Coil plug boot.
What a day!
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