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bmw4life
05-21-2009, 11:31 PM
ItÔÇÖs time to ask for wisdom from this forum. About three weeks ago I did my valve adjustment and throttle body sync. It went as well as expected and I have put in about 700 miles since then. Bike was running really smooth.
Today on my way back from work about 8 miles to home my bike started to run rough. At idle it feels like the motor is miss firing. At idle when, I do quick acceleration I can hear/feel the motor back fire (exhaust note). When I run the bike I feel some amount of power lost.
I am not sure if my ignition coil is faulty. Any ideas? Where do I start?

mpmarty
05-22-2009, 12:22 AM
Inasmuch as it is a dual spark engine I doubt it's the coil.

1. Quit riding it and pull the valve covers and check your valves again. It is possible that one came loose and got out of adjustment. If that is the case you could cause damage to the engine.

2. If the valves are OK look closely at the spark plugs, all four of them.

3. If the plugs don't tell you anything which would surprise me no end, get a compression reading on the two cylinders. Be sure you have the little switch on the right handle bar in the "off" position so you can crank the engine without generating any spark.

4. If the compression is even and good on both sides put it back together and run the throttle body sync. again.

If you haven't found the problem by this point if it was mine I'd trailer it to the dealer.

Good luck.

leadfoot
05-22-2009, 01:08 AM
Also, since you performed a TB Sync, make sure that the jam nuts for the cable adjustment have not become loose, allowing the TBs to drift out of sync. I found I had to shave my wrenches a little in order to get a good turn on them.

I always check the simple stuff first.....Good Luck!

deilenberger
05-22-2009, 02:25 AM
It would be helpful to know what year your hexhead is.

IMHO - it could be a failed coil, the symptoms sound right, and the finger-coils have been known to fail. It is also worth checking that the coils are fully seated on the plugs since you had removed at least the primary coils to do the valve adjustment.

If I had to guess which coil failed - it's probably a primary coil that failed - not the secondary coil. I have heard when the secondary coil fails the engine buzzes more - but runs OK. It might be worth eyeballing at least the primary coils, I have seen photos of some failed ones where the coil expanded and cracked the outer casing when it shorted out. A visual clue like this would be a dead giveaway.

If you know someone with the GS-911, you might try hooking it up to see if there are any stored codes. I'm fairly certain the new engine control units are capable of recording misfires. That would be a great big clue.

BMW has changed PN's on the coils at least once, which to me means they have a new supplier due to problems with the coils. BMW has used the same design coil on numerous cars since about 1991 - and has changed vendors and extended warranties because of coil problems. (BMW usually changes PN's if a part is superceded by an improved part. Identical parts from different vendors normally keep the same PN.)

It's actually the reason I have a complete spare set for my bike in my garage - I'm calling on Eilenberger's Law of Spares (You'll never need what you have..) If you were close to me I'd say ride by and we can try swapping them out. It's not easy to test the coils - since sometimes the fail under load.

HTH,

blongb
05-22-2009, 03:03 AM
I just had the rough idle issue (along with elevated idle speed) after a dealer servicing and it turned out to be a loose vacuum hose.

tbryant
05-23-2009, 12:48 AM
I was just gonna say, my R1200C did that recently and found one of the intake tubes to the left cylinder had backed out...confuses the heck out of the system, causes backfire on accel.

bmw4life
05-23-2009, 12:34 PM
O.K this is does not make sense. I had this problem occur on Thursday evening on my way back from work. Friday morning I started my bike (no problem) and let it run for ten min at idle to reach normal working temp. Run like normal. Played with acceleration and had no issues.
Took the bike out for about 150 miles ride and run like normal. Only difference between Thursday evening and yesterday was the temp. On Thursday the outside temp was 85 F and Friday it was 72 F..
Well I guess I would just need to monitor and see if the situation occurs again. Thanks for the advice.