VFR800 5th gen motor hesitates or dies when bumps on road

Hi guys,

been tapping on VFRworld for many infos so far, and I appreciate alot the amount of experience and knowledge found here. I bought my first bike last year (2015), a VFR800 manufactured in 2000 that was already at 68,000km, love the bike. It's now at 78,000km, had no problems since then, appart from both headlights burning at the same time at 02HAM on a slippery road (downgraded the fuse from 20A to 15A, no issue yet).

To make a long story short, had a particularly bumpy road (at slow speed) last Thursday, and on the way, the bike started to hesitate, and then die, when bumps came accross. Could restart without problem every time (while rolling). Dash never shut down during the ride (looked at battery connections, tight, no rust). Was able to travel the 40km back home, but pulled the clutch every time I rolled on a bump, which allowed for no motor dying along the way even though hesitations were felt systematically.

Have to say that I replaced the 4 spark plugs 2 weeks prior, and yesterday checked all four, unscrewed and screwed them again, made sure the wire connection came with a click. All good. Found on VFRworld details on how to get and interpret the fuel injection self-diagnosis (also got the service manual in .pdf), shorted the service connector and got the zero blink result (from the FI indicator). However, when key turned to ON, the FI indicator lights up. But it turns off when motor runs.

So not sure how to interpret this no blink result, especially knowing that the light comes on upon ignition, and engine does not operate normally.

Took off left fairing, found grey connector (not blue in my case, probably replaced by previous owner), no melted connection, no rust, all clean. Same with the green wire and screw on frame for ground.

Does that ring any quick bell?

Thanks in advance,

Eric

 

Check the main 30A fuse holder (it's white plastic, clipped to battery box). Innards get cripsy over time, if so replace. Pull fuse, I bet the blades are white powdery oxide goodness. Make sure the door to your ECU is secure and clipped down (under seat, towards rear tail light. 2 plastic pop rivets at front of lid flap), otherwise the thing will slide around causing all sorts of issues.

 

Did you make any changes to the foot pegs? You are not kicking the side stand on the bump?

Check that the side stand is not loose or flopping or any bolts have fallen out. You can also bypass the kickstand safety switch as a test of whether it requires replacement.

 

V4toTour, 30A white fuse holder good, slight white powder on blades, but nothing excessive; lightly steel-brushed them in case. ECU door clipped, 2 large connectors unclipped and clipped again to make sure.
Knight, side stand has full clearance, isn't touched by surroundings, spring is strong, and it needs to be pushed down by more than 45 degrees to have the switch kill the motor.

I have a doubt: when bike in operation, FI indicator is always on when motor running? Mine, again, lights up on ignition, but closes after 2-3 seconds (motor running). If the PGM-FI is off, that could explain the motor hesitations and tendency to die upon vibration. But what could have the PGM-FI it turned-off?

Thank you again for your help

 

ECU - If you didn't you must check the individual wires to make sure they are all tight.

Does the problem still exist after you did this cleanup?

* Find the bank angle sensor and make sure it is not a-floppin'. (Can't help as I don't know where mine is).

 

After a long week without use of my VFR, was finally able to remove all 4 fairings and inspect all accessible connections with relays and harness.
Bank angle sensor was tight and connections clean.
Grounding screw and green wires on frame on right side of bike were clean and tight.
Checked individual ECU wires on both connectors, nothing loose.
Was too late so didn't have time to check connections under the gas tank, but took a chance with a test drive. To my surprise, initial symptoms were not reproduced (tried on bumpy road, headlight on HI, 7-8000RPM, motor stayed strong). So I'm stuck with a loose connection somewhere, and preventive measures will be to clean and lightly brush these connections once a year (dielectric grease not necessary since little or no oxydation found).
Might go for the VFRness.

Thanks for the help!

 

Or...in the process of the inspection, you have disconnected and reconnected the cause and now have good continuity.

BTW you asked about the FI light, it should come on for a few seconds with the ignition, then go off if all is normal. If you get a fault with the FI system it will illuminate and stay lit. If that occurs there is a diagnostic method (see the service manual) where the light can be made to blink out a code that identifies the fault.