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I have a 2006 GL1800 HPNA with 171,800 miles. Recently, it started misfiring. It only happens at certain times, though.

The bike runs perfectly while the engine is cold. The first half mile is great. I've been smelling unburned fuel when I stop at a light for some time, so I think it's running rich while it's cold.

Once warmed up, the engine sputters badly, but only up to about 2500 to 3000 RPM, when it starts running great again. The RPM it stop misfiring at is lower in first and second gear because the load is lighter. When it reaches the RPM where it decides to run right, it's like a switch is turned on. If I'm taking off into a turn, I have to be prepared for the sudden power surge.

I took auto mechanics in high school, so I know how an engine works. That was back in 1978, so I'm really not qualified to diagnose a modern bike. I changed the plugs because it was quick and easy, and the local Honda dealer had the fuel injectors cleaned, with no change. The dealer wanted another $800 to continue diagnosing, so I had them put it back together and return it to me.

The problem is affected both by the engine temperature and the RPM. My thoughts are the ignition advance mechanism, or the fuel scheduling computer. I thought it might be the temperature sensor, but the gauge on the panel is still behaving as it always has.
The dealer thought it might be the ignition coils or wiring, but that would cause a sporadic and intermittent misfire, and the problem is very consistent.

I'm hoping one of you out there has seen this problem before, and any advice you can give will be appreciated.

Thanks, Joe
 

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My automotive mechanic/heavy duty mechanic/hot rod builder friend says warm engine misfires are usually ignition system problems.

He said to first, change the spark plugs. You've done that.

Second, replace the spark plug wires.

If that doesn't fix the misfire, continue diagnosing the ignition system, but you start by replacing the cheapest ignition parts.

Good luck.

Tim
 

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Is try a set of new plug wires, it’s possible the ECM is crapping out once at operating temperature. Also could be a connection with corroded prongs.
 

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Does it ever throw an FI code? If so that should be your starting place. If I had to make a wild guess, I’d suspect the crank position sensor as they are known to be temperature sensitive. But, if that is acting up enough to cause a consistent misfire, it should throw a code...(?).

Some folks smarter than me will will be along shortly...

:thumbup:
 

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I have a 2006 GL1800 HPNA with 171,800 miles. Recently, it started misfiring. It only happens at certain times, though.

The bike runs perfectly while the engine is cold. The first half mile is great. I've been smelling unburned fuel when I stop at a light for some time, so I think it's running rich while it's cold.

Once warmed up, the engine sputters badly, but only up to about 2500 to 3000 RPM, when it starts running great again. The RPM it stop misfiring at is lower in first and second gear because the load is lighter. When it reaches the RPM where it decides to run right, it's like a switch is turned on. If I'm taking off into a turn, I have to be prepared for the sudden power surge.

I took auto mechanics in high school, so I know how an engine works. That was back in 1978, so I'm really not qualified to diagnose a modern bike. I changed the plugs because it was quick and easy, and the local Honda dealer had the fuel injectors cleaned, with no change. The dealer wanted another $800 to continue diagnosing, so I had them put it back together and return it to me.

The problem is affected both by the engine temperature and the RPM. My thoughts are the ignition advance mechanism, or the fuel scheduling computer. I thought it might be the temperature sensor, but the gauge on the panel is still behaving as it always has.
The dealer thought it might be the ignition coils or wiring, but that would cause a sporadic and intermittent misfire, and the problem is very consistent.

I'm hoping one of you out there has seen this problem before, and any advice you can give will be appreciated.

Thanks, Joe
Sounds like you've got a coil breaking down. Could be a cracked coil. The most common coil complaint is that it will run fine until warm and then start to miss. With the mileage you have on her, I'd replace the plug wires too while I was at it.
 
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