Odd running

Discussion in 'Mechanics Garage' started by kjg, Jun 18, 2022.

  1. kjg

    kjg New Member

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    Hi
    new to the group but may i ask a question?

    my 2014 vfr800 vtec runs great bellow the vtec point but as soon as the revs hit the point that the vtec cuts in the bike wont rev past this.

    the bike is totaly stock and fully serviced .

    any ideas why I cant get the revs past this point?

    many thanks for any thoughts.
     
  2. Grum

    Grum New Member

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    Wow, this is most unusual for an 8gen, or any vtec 6gen for that matter.

    - Does your Fi light (MIL light/engine fault light) come on?
    - Has it only done this since a recent service?
    - How many K's/Miles has it done?
    - Are temperature indications and oil levels all OK?
    - Is the engine fully warmed when this happens?

    Don't have the vtec spec for the 8gen, but the 6gen states engine temp must be above 65degC/149degF for vtec ops.

    I wonder whether the VLC Solenoid is actually operating, meaning, the vtec valves are not kicking in when they should be at that RPM.
    Grasping at straws! Maybe something as simple or crazy as a blocked or very dirty Oil Filter limiting oil pressure for vtec valve ops!

    Not vtec related but a dirty fuel filter is another possibility!

    Keen to know the cause/answer to this one! Keep us posted.
     
    Last edited: Jun 18, 2022
  3. kjg

    kjg New Member

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    Hello Grum, thanks for the reply.
    No Fi light showing and the service was a good few hundred miles ago.
    The bikes got 26,000 miles on the clock all trouble free.
    Oil levels good and and temperature looks normal.
    Yes did a 40 mile ride and the problem was still there so should have
    been well up to temperature.

    I always have the oil filter replaced with every oil change and tend to use genuine Honda
    filters.

    lovely bike but a bit of a mystery.

    cheers kevin
     
  4. Grum

    Grum New Member

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    Hi Kevin.

    Well I guess if it was my bike and if I suspected it is related to vtec operation, the first thing I would do is check for any ECM fault codes stored in memory, then establish that the ECM is outputting 12v or not to the VLC Solenoid when vtec is activated. I have a very tiny digital voltmeter which I could temporarily wire into the wiring as close to Solenoid as possible, (the wiring diagram shows that from the ECM and apart from the ECM connector, there are two other connectors that the single wire for the solenoid goes through) then tape the meter up front somewhere, go for a ride, seeing if the voltmeter reads 12v at the point of vtec. If that was O.K. I would independently power the Solenoid and make sure I can at least hear it operate, just a starting point!


    It's all about how mechanically minded you are, and whether you have the Service Manual, multimeter and understand the wiring diagram. The fault you have I've never heard of before, the vtec system is incredibly reliable, and add to that the VLC Solenoid is buried within the Vee under the Throttle bodies, a pain in the ar@e to get to.

    As far as a fault code from the ECM there is only one for the VLC Solenoid - a Code 27, the ECM can only know if the wiring or solenoid coil has gone open circuit.

    Perhaps whoever does your servicing should look at it OR a reputable Honda Motorcycle service specialist.

    A couple more questions.
    - Does your engine start instantly when cold?
    - Is your battery healthy and terminals clean and tight?
    - Are you confident the fault was not there straight after its last service?
    - Bike stationary can you rev it (momentarily) up to say 7000rpm?
    - Does the bike surge or carry on in some way when it gets to max rpm while riding?

    Good luck, I'm struggling to offer any more advice. Perhaps there are others that might chime in with some ideas. Keep us posted.
     
    Last edited: Jun 19, 2022
  5. kjg

    kjg New Member

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    Hi
    Well a semi eventfull day. i talked with the local Honda dealer to se about booking the bike in to be looked at.
    After describing the bike and the problem the service guy said most likely a stuck exhaust valve.

    Now im not totaly convinced by this but i running out of ideas.

    Cheers kevin
     
  6. Grum

    Grum New Member

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    Hi Kevin.
    "A stuck exhaust valve", I guess he's referring to the vtec valves as your bike would be running like crap if it wasn't.

    - Just a thought, are you sure that the Throttle is not jamming for some reason? Is there more throttle movement beyond the max RPM your getting. To be sure you could remove your airfilter and check that from idle to full throttle the butterflies go from closed to fully open?

    Before diving into or surmising serious valve issues, the VLC Solenoid MUST first be confirmed as operational and/or its ECM drive signal as good, it's absolutely fundamental to vtec operation.

    Something you could try - Unplug the VLC Solenoid electrical connector and ride the bike. You should get the Fi light to come ON and if there is NO change to how the bike performs then this could confirm an issue with the VLC Solenoid, worth a try. This would involve at least removing the air box to get access to the single wire connector for the VLC Solenoid, bit of a pain! At this point with Ignition to off, you could supply a 12v signal to the valve wire and at least hopefully hear it operate or not! See attached section of wiring diagram, single wire connector for the VLC Solenoid, Green/White to White wire.

    Good luck, look forward to any news.
     

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    Last edited: Jun 20, 2022
  7. squirrelman

    squirrelman Member

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    good thing grum is on the case ! nobody on this forum knows more about motorcycle electricks :cool:
     
  8. Grum

    Grum New Member

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    Thanks Mate, but seriously, that is a gross exaggeration! :Redface:
     
    Last edited: Jun 20, 2022
    mello dude likes this.
  9. Terry Smith

    Terry Smith Member

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    Maybe rodents have moved into the airbox and filled the air filter with useful (if you are a mouse) things that are impeding the airflow needed for higher revs?
     
  10. squirrelman

    squirrelman Member

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    ^^ could be

    001_1HIMeeeml.jpg.6a6cbfe4c93681f7dd29f32c831696a6.jpg
     
  11. Terry Smith

    Terry Smith Member

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    Is your little friend admitting to doing bad things in the airbox? Certainly looks guilty!
     
  12. squirrelman

    squirrelman Member

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  13. kjg

    kjg New Member

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    Hi sorry for the delay in replying to my thread and your replies, work and life took over. Well finaly managed to get the bike into a Honda dealers for a diagnostic. The verdict? they dont know but suspect a vtec Bucket gone bad! but I cant tell yo im convinced, the more I delve into this engine the more I suspect the VLC solonoid is the issue. Grom, thank you I think disconecting the VLC has to be the next option.
    I may of course be barking uo the wrong tree.
    The main dealer gave me a ball park figure of £1700 to strip and rebuild both cylinder heads, great price for the dealer not so good for me.
    Thank you guys for your input
     
  14. Thumbs

    Thumbs Member

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    Who are the Honda dealers?

    Does the bike rev past 7k when stationary?

    These motors are so over engineered and I’ve never heard of a valve bucket failure on any VFR

    The valve covers are not difficult to remove then you can see for yourself
     
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