My intermittent power loss has returned after an absence of 2500 miles. (Original thread: http://forums.bmwmoa.org/archive/index.php?t-65698.html)
Short version: Occasionally (3-4 times in 60 miles, in this case), the engine loses power. After a second, or three, it comes back on.
I previously had a bad kill switch that would shut everything down when it jiggled out of place. This doesn't feel like that. Not catastrophically jerky. The engine is just not there.
It will restart with the clutch held in, so it is not bump-starting itself. It has not (yet) died for a long enough period for me to get off the road.
All that, along with normal spark plug appearance, makes me think I have a fuel supply (or maybe air-related) issue rather than an ignition issue.
I've replaced the usual obvious suspects - fuel filter (several), spark plugs, crankcase vent hose, all fuel hoses, big rubber elbow after the air meter, gas tank electrical connector (but not the whole sending unit - yet). The gas and the tank are clean. Injectors just cleaned by Mr. Injector after the first failure 2500 miles ago.
I suspect an electrical fault in the fuel supply, either killing the fuel pump or the injectors. A failure of the pump or pressure regulator would yield the slightly smoother shutdown (as compared to the total electrical failure of the bike). Here are my (current) diagnostic questions:
1. Does it sound like that's the right direction, or am I barking up the wrong tree?
2. Because it's so intermittent, and brief, I have near zero ability to observe what's happening with the bike when the failure occurs. So my thought is to tap critical fuel-related electrical points (like fuse 6, and the coil side of the fuel pump relay) to power LEDs mounted next to the cluster. When the issue occurs, if current is lost at one of those points, its LED will go out. Assuming I don't have too many of those LED's, a quick glance will tell me if any of them is out, and I can follow up with focused examination of the indicated area. Does this seem sane, and at least plausibly productive?
3. Assuming it's not insane, the hardest point to tap (yet possibly the most relevant) is the two connectors on the fuel pump itself. (Either power or ground could fail, of course.) Any suggestions on how to temporarily route wires into the tank?
4. To test a ground connection, like, say, the ground on the fuel pump itself, I'd need to run power to an LED from a known good source, and then ground it through the suspect ground wire. Does that potentially introduce grounding problems for the component (e.g. fuel pump)? I don't think so, but best to ask; I don't want the diagnostic process to cause new failures.