Engine Cutting Off Electrical Problem? - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 11 (permalink) Old 08-20-2019, 01:14 PM Thread Starter
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Engine Cutting Off Electrical Problem?

This problem occurred a few times when I first purchased the bike about a year ago but is now getting worse. Shop that worked on it then suspected the bank angle sensor and repositioned it. Problem seemed to be somewhat fixed but still occurred only on rare occasion.

Bike starts and runs fine. However after riding about an hour today, it cut off 5 times. It is entirely random and not when I hit a bump or turning etc. Occurs in different gears and different rpms. It is like hitting the "kill switch" and engine just stops. The only dash light that comes on is the oil pressure light. Headlights still work normally after engine has died. Normally after turning key off and then back on bike fires back up until this happens again. However today on two occasions, bike would not start. I let it sit for about 10 minutes after several unsuccessful starting attempts and finally started back up and ran normally. I have noticed I still get the fuel pump "whine" sound when it would not start. I am not getting a fuel injection light indicating a problem and comes on normally when starting.
Trying to get some ideas how to trouble shoot this intermittent but increasing in frequency problem because fear it is eventually going to leave me stranded on the side of the road. All maintenance has been done on the bike and up to date. I was going to start by taking the kill switch apart to look for corrosion etc. I have also checked battery which is new for loose connections and the ground.

After the ride, this is what I have done and not found any obvious problems:
Removed left fairing, seat cowl and raised the tank to search for any obvious wires that were frayed or not seated properly. I replaced the fuel cutoff relay with a spare that I purchased some time ago. I removed the headlight relay and noticed it appeared "older" and while not in terrible shape, the connectors appeared somewhat discolored compared to the new one. I moved the fuel cutoff relay to the headlight relay position. While inspecting all of the connectors I could get to with the tank up, I used dielectric grease to apply to the connectors. Inspected the sidestand "green connector" under the tank and applied grease. Took apart the engine stop/run switch and applied dielectric grease but did not note any problems. The bike does not have a power commander. Planning to ride it again today and see if the problem continues. I realize this is probably a "shotgun" approach to fix this intermittent problem and any ideas or other things to check would be appreciated?

Last edited by robertj1979; 08-21-2019 at 07:43 AM. Reason: Update
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post #2 of 11 (permalink) Old 08-21-2019, 04:24 PM Thread Starter
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Update. Rode bike today after performing as above and same problem. Bike would not start when hot. Once cooled down, started normally again. Very frustrating. Wonder if fuel pump could be the problem or if it is somehow heat related as it is running around 200+ now when it quits and then does not want to start until cooled down somewhat. It is possible that is coincidental but just thought would add that every time it quits and does not want to start it is on the warm side. Also, as far as I know the fuel filter has never been changed but at this point would suspect fuel pump or an electrical problem. Hope Wibbly or others have a suggestion or next stop is the shop who is backed up at least two weeks. Thanks in advance.

Last edited by robertj1979; 08-22-2019 at 09:53 AM. Reason: Addition.
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post #3 of 11 (permalink) Old 08-23-2019, 10:26 AM
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it sounds like you're losing spark. if it were the kickstand sensor there's an easy test, just leave the bike in gear, clutch in and see if it will crank, if it won't then the sensor is tripped. you could simply jumper out the kickstand to rule it out completely.

another place i'd look is the crank position sensor and cam position sensors and their associated wiring. it could be an intermittent short in those cables as the ecu needs those signals to fire the plugs. (also check for corrosion on any of these wires in their associated connectors right back to the ECU)

i doubt it's CDI at this point simply because those failures tend to be permanent.


one thing it COULD be but i'm not totally sold on the idea is if someone did a hackjob soft rev mod. the mod requires you to splice into the main power to the ECU. if that splice is done with a scotch lock or similar it may be cutting ECU power. however i'd exect this issue to be more prevalent than you describe. but it's worth a look.

similarly you can check all points along the EFI power circuit. check the IGN fuse holder in the fuse box is tight and secure, check the kill switch connections (white black/ and black) are secure and tight, check the engine stop relay is good (all pins in the connector grab firmly on the tabs in the relay, no corrosion), check that the BAS connector is the same way (you could bypass the BAS to see if that's an issue by connecting the red and green wires in the green 3 pin connector).

also check that the fuse holder that holds the 30 amp main efi fuse is secure, anything loose in there will cause grief, similarly the 1 pin main connector on the red/white wire could be loose or corroded.




once you've been through all that it's likely you won't find any issues anymore. there's no way to be more specific i'm sorry.
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post #4 of 11 (permalink) Old 08-23-2019, 04:33 PM Thread Starter
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Thank you. That is exactly what I needed and will check all those points you suggested. Away on business but will definitely check all of those points when I get back. I really think this problem existed when I bought the bike but for some reason mysteriously went away for a while. I checked the 30 amp main efi fuse and connector/wire as far back as I could without removing more parts. I did not check the fuel pump connector in the tail section however and need to do that as am wondering if the fuel pump could be stopping intermittently. It sounds like the fact it is running a little hotter now due to the time of year is coincidental and should not effect the fuel pump operation? As far as I know the fuel filter has never been replaced. I definitely think I will eliminate the kick stand switch as suggested because have not done that yet either. Unfortunately much of the splicing that was done for the led lights and fender eliminator was a "hack job". The guy who owned the bike before me actually installs trailer hitches for a living and it was amazing to me how he could have done such a crappy job with connectors that I have already had to redo/replace. I am not in that kind of business and am admittedly an amateur when it comes to mechanics but was obvious to me how hacked up the wiring was when I got to examine it.
Really appreciate you taking the time to help out on this and will report back when I find the problem. If I am unsuccessful it is going to my mechanic who restores vintage motorcycles and is an ex indy car mechanic who has been very helpful but stays "swamped" with work on bikes which is now his full time business.

Last edited by robertj1979; 08-23-2019 at 04:38 PM. Reason: Addition
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post #5 of 11 (permalink) Old 08-26-2019, 01:18 PM Thread Starter
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Happy to report I think the problem is solved. I rechecked the single ignition wire with the 30 amp fuse and while not disconnected the splice connector had a few frayed wires so I reconnected and replaced the splice. Disconnected the kickstand switch and jumped the connector to disable it. Disconnected the BAS connector and disabled that as well. After a ride today of almost an hour did not have one shutdown. I probably should have done these "one at a time" but was getting very aggravated and just want the problem to be "gone". I noticed when I disconnected the Bank angle sensor previous owner had already "spliced connections in that line for some reason so just wanted to take it "out of the equation" for now. The only issue now is not exactly sure which "fix" took care of the problem and would really like the BAS to work for safety reasons so may just order a new one and replace and see if the problem comes back.
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Last edited by robertj1979; 08-26-2019 at 01:21 PM.
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post #6 of 11 (permalink) Old 08-26-2019, 02:52 PM
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Nice. It sucks to have a problematic bike. I'm glad my direction led you to a solution
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post #7 of 11 (permalink) Old 08-26-2019, 04:54 PM Thread Starter
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Upon further inspection of the BAS after I removed it, I noticed that the wires had been spliced so that it could be relocated toward the back of the tail section. After the botched fender eliminator, I am assuming there was no good place to mount it so someone used smaller gage electrical wire and extended its length. I have ordered a used BAS from Ebay that should be here in a couple of days and am trying to figure out how to mount it close to the connector in order to not have to extend/splice the wires. The wires were cut so close to the connector it is going to be difficult to splice into it again. I am wondering if the smaller gage wire spliced into the BAC wires could have been the reason for the problem? If I have to splice into those wires to relocate it to the rear I will definitely get heavier gage wire that is at least as large as the oem. Thanks Wibbly cause you really pointed me in the right direction.
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post #8 of 11 (permalink) Old 08-26-2019, 05:03 PM
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the bas has almost no current going through it. wire gauges aren't likely to be the culprit unless they've failed mechanically.


you can buy the terminals for those connectors at cycle terminal

hell you can just buy a new green 3 pin .110 connector and build your own.


Motorcycle 2.8mm - 110 Connector and Terminals
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post #9 of 11 (permalink) Old 08-27-2019, 10:33 AM Thread Starter
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Ok. Understood.. Thanks for the info and where to get the connectors. I found the BAS on Ebay for $9 but no guarantee it is good I suppose but worth a shot for that price to see if that solves the problem once the BAS is reconnected.
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post #10 of 11 (permalink) Old 08-29-2019, 03:56 PM
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Originally Posted by robertj1979 View Post
...Disconnected the kickstand switch and jumped the connector to disable it...
Curious if you're planning on reconnecting this. I know if I disconnected mine it would eventually bite back. My last track day I saw 3 different guys riding through the pits with their side-stand down. They'd turn left and then WHACK!
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