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Misfiring in the rain


Charles Elms

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Charles Elms

I was riding in my first rainstorm of the season yesterday and after about 5 minutes at 70 mph in a moderate to heavy rain the bike started running very rough and misfiring. Felt like is was alternating between running on 2 and 1 cylinder. Speed dropped to about 50 mph and I managed to keep moving by downshifting to 4th. It seemed like about 10 seconds of every minute the bike would run ok, 10 seconds like it was not firing at all, and the rest of the time it was running on one jug. Bike is a 97 RT with 62000 miles. I am have the original HES but figure it is not the problem because my understanding the HES works or it doesn't, and will not cause the bike to run on one cylinder.

 

Before I tear the bike down and start poking around at all things electric- any suggestions as to what the culprit might be?

 

It was misfiring when I pulled it into the garage. I will take it out now that it's not raining and verify that it runs ok and the misfiring was caused by the rain.

 

All suggestions will be appreciated.

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Normally an HES insulation failure seems to cause the engine to quit completely but given your symptoms (and bike model/mileage) I sure wouldn't rule it out. Your problem may also lay in some other part of the ignition system but since you are a prime candidate for an HES wiring harness upgrade (and it should probably be done regardless of whether it is the source of the current problem or not) it seems like you have nothing to lose by starting there.

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This is just a personal feeling, so take it for what it is worth.

 

My bike used to act up in the rain.......it would occasionaly misfire (not as bad as you explain, but it was still there), I occasionaly had a noticable loss in throttle response, and it would also have a tendancy to stall at stop lights and stop signs. It only acted like this while I was riding in the rain.

 

My HES died last month (the morning after riding 100 miles in the pouring down rain). I replaced it, and haven't had any of those symptoms return. I got lucky and made it home last night before that storm hit, but I got stuck in heavy rain twice last week and the bike never skipped a beat. In fact, since the HES replacement, the bike has never run this well in the two years I've owned it.

 

The only thing that changed was the HES and the alternator belt, so I have to point the finger at the HES. Also, coming from the electronics field......I have seen numerous intermitant wiring failures involving heat and humidity (I spent 7 years working on portable military radar systems). So it wouldn't surprise me one bit if this was an early warning sign of a failure.

 

I still have my old HES in the garage. I keep meaning to carefully slice open the harness and inspect the wiring, but it keeps escaping my mind when I actually have the time.

 

Once again.....its just my opinion.

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Joe Frickin' Friday
Could be aged (microscopic cracks) spark plug wires.

 

I would expect bad plug wires to show up first at high-load conditions, i.e. when there is maximum impedance at the spark gap, forcing the wire to arc to ground somewhere else. OP says it was misfiring even at idle in the garage, so I suspect plug wires are not the problem.

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Charles Elms

Just came back from a short test ride. Now that it's dry it runs smooth as silk. I'll start with the HES since I know it's only a matter of time before it bites me. I'll also go over the plug wires carefully.

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Just came back from a short test ride. Now that it's dry it runs smooth as silk. I'll start with the HES since I know it's only a matter of time before it bites me. I'll also go over the plug wires carefully.

 

Are you going to do the work yourself, or are you thinking about a dealership?

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Charles Elms

I'm going to do it myself. I'm going to replace HES and plug wires. 10 years is good enough for me on those parts.

I will order parts from BeemerBoneYard today.

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I'm going to do it myself. I'm going to replace HES and plug wires. 10 years is good enough for me on those parts.

I will order parts from BeemerBoneYard today.

While you're in there it's probably best to upgrade the HES harness wiring to something that will take the heat. An OEM replacement will just be putting the same potential for a problem back in.
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I was riding in my first rainstorm of the season yesterday and after about 5 minutes at 70 mph in a moderate to heavy rain the bike started running very rough and misfiring. Felt like is was alternating between running on 2 and 1 cylinder. Speed dropped to about 50 mph and I managed to keep moving by downshifting to 4th. It seemed like about 10 seconds of every minute the bike would run ok, 10 seconds like it was not firing at all, and the rest of the time it was running on one jug. Bike is a 97 RT with 62000 miles. I am have the original HES but figure it is not the problem because my understanding the HES works or it doesn't, and will not cause the bike to run on one cylinder.

 

Before I tear the bike down and start poking around at all things electric- any suggestions as to what the culprit might be?

 

It was misfiring when I pulled it into the garage. I will take it out now that it's not raining and verify that it runs ok and the misfiring was caused by the rain.

 

All suggestions will be appreciated.

 

Charles, you could have one of more of many possible things.. As mentioned above-- could be Hall sensor,, or plug wires,, or hairline crack in spark plugs,, or coil insulation problems,, or even more than one isolated thing..

 

About all you can do is eliminate the obvious,, like cracked spark plugs,, poor fitting spark plug boots,, obvious cracks in the spark plug wire outer covering,, plug wires abasing on sharp edges,, etc.. If nothing obvious found then probably at least pull the Hall Effect sensor & look for problems there..

 

One obvious place to look is at the R/H spark plug wire where it comes close to the R/H TBI cable cam.. My last 1100 had hard contact there & was wearing a thin spot in the spark plug wire..

 

If you want to go to the trouble you might pull the Tupperware off then run the engine at night (or in the dark anyhow) while spraying a fine mist from a garden hose on different engine areas just to see if you can duplicate the engine misfire or see obvious sparks jumping..

 

Twisty

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I'm going to do it myself. I'm going to replace HES and plug wires. 10 years is good enough for me on those parts.

I will order parts from BeemerBoneYard today.

 

Sounds good. Its much more straight forward than I thought it would be. It would have been a cake walk if I would have been in my garage when mine failed. I'm interested to see if it solves your problem also.

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I'm going to do it myself. I'm going to replace HES and plug wires. 10 years is good enough for me on those parts.

I will order parts from BeemerBoneYard today.

 

Just a hint:

The stock BMW HES is already failing. Why buy another one? I just picked one up from BMWMick (on this board) for less $ and better wiring (high heat). Get a hold of MIck thumbsup.gif

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