Hesitation / Misfire after a hard braking event

May be just a coincidence but after a hard braking event (I'm talking full ABS actuation poo came out kinda thing) my bike has a random/intermittent misfire. VERY noticeable on cold start with the idle-up but even at operating temp it'll hesitate.
Example 1: Sliding the clutch when leaving from a red light, breaks up really bad at low RPM. Higher RPM, I'd say VTEC engagement +- 1500RPM is fine.
Example 2: Steady throttle, highway speeds, 6th gear. Twist to pass, usually has plenty of giddy up to overtake, but now feels like it's in 8th gear. Just bogs. After a few seconds it clears up and almost slides me off the back of the seat.

Working on attaching the idle video I took...

 

https://vimeo.com/200977335

 

No one has replied yet so I'll give it a shot. Firstly I can't see how braking hard could possibly cause your bike to misfire. It's likely misfiring also at higher rpm but you just don't notice it. This explains why it won't pull in higher gears.

I would check your spark plugs first. I don't know when you changed them last but it's seems clear when idling that the bike appears to be cutting in from 3 to 4 cylinders.
I'd check the exhaust pipes and see if one is much colder than the rest, after it's been running a few minutes from a cold start.

If the plugs aren't the problem I would think you have some kind of electrical fault.

A possibility is bad gas, or a blocked fuel filter.

It's trial and error if you don't have diagnostic tools. Find out which cylinder is causing the misfire and go from there.

 

One remote possibility for the hard braking misfire could the bank angle sensor, which is designed to stop the ignition system if the bike is crashed. If this is loose and moving around on it's mount, you might get those symptoms. The sensor is located in the front cowl, top left.

 

Okay so I took her all apart today. Cut the connectors out of the R+R and spliced together. No change.

While running I pulled each coil connector and found the misfire coming from cylinder 4 (front right). See attached video.

Cool doesn't show any signs of arcing, nor does the plug.

https://youtu.be/4w1OW9bILck

 

That is good that you've isolated the fault to a single cylinder; means there are only a handful of components that can be astray, the low tension wire, the coil or the HT wire/cap. So maybe a small break in the #4 low voltage coil wire that causes intermittent running? I think you can unplug the ECU and find the matching wire in the plug and do an end-to-end continuity check while wiggling the wire. If not that, maybe time to replace the coil on plug. Have you replaced the plugs?

 

Spark plugs are original 10,800 miles.

Swapped coils between cyl 2 and cyl 4 and 4 still has the problem so the coils we know are good.

I had been planning on putting new plugs in her but have been holding out until I figure out my overheating issue (possible head gasket, another thing that could be causing the misfire).

I'm thinking of a do-over on the compression test, with extra attention to #4...

 

COLD Compression test results:
Cylinder 1 145psi
Cylinder 2 140psi
Cylinder 3 140psi
Cylinder 4 140psi

I did notice a bit of leak down but I'm not sure if it's the engine or the tool so don't jump to conclusions on that one...

 

Just switch the plugs over.. you will then be able to eliminate that as the issue..

Personally, I work on the basis of if I have to pull a plug, I put a new one in..

 

On my ST1100, I finally cured an occasional misfire with a set of new plugs. A cheap thing to do to eliminate a potential fault.


Sent from my iPhone using Tapatalk

 

Yeah I have a set ordered from Amazon

 

Quick update:

New plugs in, haven't fired her up yet because I'm a dipshit and tore the fuel rail return line when I let the gas tank tilt over too far. I swapped #2 and #4 fuel injectors to see if the misfire moved (assuming the plug don't sort that out.

I was able to look down the spark plug holes and saw no evidence of piston tops being steam cleaned by coolant, so that along with a good compression test and a good cooling system pressure test I'm gonna say the head gasket is good.

On the overheating front; I got a gallon of "Engine Ice" coolant, recommended by the guys at my local Honda powersports dealer for warmer-running bikes. I will be removing the radiators to see if they're plugged (left one cool to the touch, while right one is blistering) and installing a brand new radiator cap and thermostat.

I found a 210 on/190 off fan switch from Be Cool part number 75099 but it's a 3/8NPT thread so I also sourced a M16-3/8NPT adapter which should all jive and keep me running cool.


Next full day off is Wednesday where I'll hopefully have her running again and I'll report back...

 

FINAL UPDATE:

New Plugs
New Coolant (engine ice)
New Thermostat
New Radiator Cap
Cleaned Throttle Bodies
Repaired Chewed Knock Sensor Wire
Lubed Brake and Clutch Levers

BIKE RUNS MINT!!!!

Not sure what did it, but my money is on the chewed Knock Sensor wire.

Also to note: Engine Ice is amazing stuff, quick test ride in 45 degree ambient kept the coolant temp between 165 and 168...crept up to 172 at a red light. Will report back when its 90* and I'm sitting in traffic on the cross Bronx expressway.

 

Congratulation on persevering with this one!