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Engine misfiring when warm


Pixie
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Start with the battery for it's the weakest link in the whole system... To
determine the condition of an Maintenance Free battery give it a
refreshing charge... wait 30 minutes... measure terminal voltage...

12.8 or higher is a good battery...
12.0 to 12.8 is a insufficient charge... recharge...
12.0 or lower... battery unserviceable...

 

The key to understanding a motorcycle charging system is RPMs... below
5000 and the bike consumes more than the system can replenish... above
5000 and the battery stores more than the system can use...

We are in the age of the Electronic Bike... fuel delivery and spark
timing and instruments and everything else operate within millionths
of a volt (milli-volts) and for some reason a component doesn't
receive its allotted share of volts the system starts to prioritized
which components are powered and which components are cut so you can
ultimately return home...

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5 hours ago, Pixie said:

Thanks, will check these suggestions out. Spark plugs was the first thing I tried, it's not that. also tried set of second hand coils, still the same.

 

Any mods?  

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8 hours ago, Pixie said:

Thanks, will check these suggestions out. Spark plugs was the first thing I tried, it's not that. also tried set of second hand coils, still the same.

 

Why didn't you mention this first up???

Anything else you've tried that we don't need to worry about?

Any suspicions of your battery, charge it then take it to a reputable auto store where they will load check it for you.

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15 hours ago, BusyLittleShop said:

The key to understanding a motorcycle charging system is RPMs... below
5000 and the bike consumes more than the system can replenish... above
5000 and the battery stores more than the system can use...

We are in the age of the Electronic Bike... fuel delivery and spark
timing and instruments and everything else operate within millionths
of a volt (milli-volts) and for some reason a component doesn't
receive its allotted share of volts the system starts to prioritized
which components are powered and which components are cut so you can
ultimately return home...

Not sure of what your saying here BLS.

- If the charging voltage is normal then the battery is being charged at any RPM.

- Millivolts = 0.001 being a thousandth of a volt. 

- ECM will use a default numerical value for a sensor that is outside of operational values.

 

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16 hours ago, BusyLittleShop said:
The key to understanding a motorcycle charging system is RPMs...   below 5000 and the bike consumes more than the system can replenish...

 

What? 

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On 11/11/2021 at 9:57 PM, BusyLittleShop said:

...for some reason a component doesn't
receive its allotted share of volts the system starts to prioritized
which components are powered and which components are cut

so you can ultimately return home...

Uhh, all sensors share common regulated 5v power-source from ECM. Same with all coils and injectors sharing one common power line directly from battery... Not sure how any kind of triage can occur...

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So if I may, I'd like to understand this better.  If you're pulling away from a stop light at maybe 4,000 to 5,000 (or whatever) rpm, you experience a mis-fire.  But once moving, maybe 40 mph, if you're in a gear that produces the same rpm as when leaving a stop and using the same throttle setting you are not experiencing a mis-fire . . . do I have that right?  In other words, is the only variable that causes or eliminates the mis-fire the speed?  That would seem very unusual but plausible.   

 

Also, when you mentioned "2nd hand coils" - do you have a buddy that also owns a 6th gen?  Just wondering how you sourced them.  The Denso part number is also common to many Honda and Acura cages, so they are common.  They do differ though from many other coil packs in that they have a 3 wire set up vs 2.  If you have any high(er) resistance connections in the circuit(s) to the coils you could potentially have issues, or any wiring with cracked insulation that could be intermittently shorting out, possibly under certain loads or conditions and maybe not others.  Some thorough inspection of the wiring and connectors may be helpful, particularly cylinders 2 and 4, which get the brunt of oncoming moisture and debris. 

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6th gen will run just fine with a bad battery and charging system issues, just like a regular vehicle will drive for a looooong while with a bad alternator.  I would check the battery and it "could be" electrical but this doesn't sound like a battery or spark problem.  

 

I would look for mods, to include PAIR valve removal.  Exhaust mods without an ECU tuner of some sort (RapidBike or Power Commander) comes to mind.  Vacuum leak or pinched tubes somewhere.  Whatever DannoXYZ and Grum say to do 😄  Run some of this through the fuel tank:

 

https://www.amazon.com/Red-Line-Complete-System-Cleaner/dp/B000CPI5Z0?th=1

 

Nothing cleans out the fuel system like PEA, and SI-1 has more of it than anything else.  

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23 hours ago, ShipFixer said:

6th gen will run just fine with a bad battery and charging system issues, just like a regular vehicle will drive for a looooong while with a bad alternator.  I would check the battery and it "could be" electrical but this doesn't sound like a battery or spark problem.  

Only until you reach a threshold where the injectors won't fire correctly! And probably the headlight current draw with a bad battery will get you to that point fairly quickly.

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ECM would fail due to low-voltage well before injectors, which are current-driven. As long as you have enough voltage to generate sufficient current to activate solenoid, they'll work. Threshold's around 9v or so.

 

Yeah, fuel-system cleaner with healthy dose of PEA does wonders. These have enough to be worthwhile:

 

- Red Line SI-1
- Techron Concentrate Plus
- Gumout All-in-One
- 3M Max Strength Fuel System Cleaner #08814
- Royal Purple Max Atomizer 18000

 

I'm still betting on vacuum leak.

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This thread keeps reminding me of another thread from a couple years back. 

 

There was another owner (of a 5th Gen, I think) who had a "misfire when warm/hot" situation, and after a lot of searching and trouble shooting he discovered that one of the coils had a crack in it's plastic covering which was affecting the coil's ability to fire the spark plug (apparently the crack in the coil cover was allowing a partial grounding of the coil field to occur).

 

I can't remember which VFR forum this thread was on, I searched around a bit but couldn't find it.  Have you done a thorough/close visual inspection of the bike's ignition system, to include the coils? 

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I found this article from Southern Illinois University Automotive program to be some interesting reading about the difference between 2, 3 and 4 wire coil packs.  Interesting that the 3 and 4 wire versions are apparently using a 5v command pulse to fire the coils.  Getting so that diagnosing these things is getting more and more complex. 

 

https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1025&context=auto_pres

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9 hours ago, Sweeper said:

Vacuum leaks really show up under acceleration more than steady throttle if I recall correctly. +1

 

Negative...

On a fuel injection system any air that gets past the throttle bodies the map
just adds the corresponding fuel... the result is high uncontrolled idle... the
fact that the problem is not continuous suggest something else...
 
However poorly insulated spark plugs do show up under acceleration...
 


To locate spark leaks look at the engine under the cover of darkness...
first spray the engine with water then start... watch for the blue
arch of a miss fire... possible culprits are 1)bad wire 2) broken
spark plug insulator 3) corrosion in the spark plug cap...

 

To disassemble the spark cap use a screw driver and note any corrosion
at the resistor and spring...

 full-45634-36698-sparkplugcapdetails.jpg

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