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Hesitation while accelerating


BarOne

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Some advice neded. I am a new owner of 05' 12RT. Picked up the bike a month ago with 800 miles on it - now has 3500 (I love this bike). On a 100 mile trip today, the engine hesitated for a full second (it felt like it was about to shut down) under hard acceleration while passing a car in 5th gear. Once the hesitation passed, the engine pulled strongly and evenly. I tried to replicate the problem several more times and was able to do so only under medium to hard acceleration. The hesitation did not occur every time and it was most likely to occur when accelerating in the higher gears (4th-6th). It "feels" like the engine is starved for fuel when it happens.

Have you folks experienced this? What can I try myself before hauling the bike 60 miles to a dealer?

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Any chance that you recently fueled up? If not... maybe a tank of bad gas?

At what rev range is this happening? Any chance that you're doing full roll-ons at revs lower than perhaps 3500? (not that that would make it happen on a properly tuned bike)

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I agree with the bad coil theory. A bad coil that won't hold a full charge would make sense. It might store enough energy for normal to moderate acceleration, but at higher RPM's and throttle position, with the dual spark less staggered or even occuring simultaneously, there is a higher peak demand for energy from the coil. Form my understanding, the coil is in part just a big a capacitor as well as increasing the voltage.

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Thanks for these ideas. I hope the bad fuel theory is correct because a bad coil sounds much more expensive. I called the dealer today and the soonest he can fit me in is September 11. Are delays like this the norm in the BMW community? Do you know if there is something I can do to test the coil?

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Sounds like your dealer is understaffed or too small for the local demand. I can usually get an appointment the same week in most cases.

 

A bad coil is easy to change... but yes, it could be a little pricey... maybe $200 each??? just a guess.

 

You should feel lucky. 60 miles to the dealer is relatively short since BMW dealers are so far and few between. I have a 100 mile drive/ride. Some may be well over 200 miles.

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Barnone-

 

Also have the dealer check for computer upgrades. An issue dealt with in the 7 series update was hesitation during acceleration. That update was a good thing for my ST.

 

Frank

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Mine did the same on holiday recently (5K miles on the clock). When I got home the dealer said 'oh it will be the Bosch plugs". Curiously BMW fitted Bosch as the mains and NGK as the secondaries. When 2 new NGK's were fitted, the problem miraculously disappeared. The dealer said he had replaced 'lots'

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In order of my preference -- bad gas, followed by the plugs and bad coil bringing up the rear. Do I understand you to say there is more than one coil? I am away from home at the moment so I can't inspect the bike but a plug change can't be too difficult. Is it?

Thanks for your replies -- keep 'em coming.

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In order of my preference -- bad gas, followed by the plugs and bad coil bringing up the rear. Do I understand you to say there is more than one coil? I am away from home at the moment so I can't inspect the bike but a plug change can't be too difficult. Is it?

Thanks for your replies -- keep 'em coming.

 

If it's like most bikes (which BMW's aren't), there's 1 coil for each spark plug and they are integrated onto the end of the plug wire. So there would be 4 coils on the newer R bikes. It wouldn't be "direct" electronic igntion if some plugs shared a coil.

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Each plug has its own coil. They come off with a bit of pulling/leverage. You need a thin wall socket to get right down to the heads - mine is a Snap-On one. The plugs are easy to change. If you have Bosch, get rid of them! BMW recommend fitting dry - no copper grease. If you want to know the part number of the socket, let me know.

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Yes. It was a rough as a bear's backside, as they say. But instantly cured. Independent dealers in the UK are recommending Brisk plugs now....

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