1999 VFR800 Unsolved Misfiring Problem

Discussion in 'Mechanics Garage' started by RockVFR, Sep 14, 2009.

  1. RockVFR

    RockVFR New Member

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    I've had a problem with my bike for quite some time now. It seems to come and go intermittently and the symptoms have changed relatively as well over the past 2 years. The problem causes the bike to misfire. It seems to be relative to the engine temp and to a lesser extent the ambient air temp. The bike seems to run best at cooler temps, from 35 - 75C, V.Smooth idling, good power delivery through rev range etc. After 75C things start to go a bit funny.

    At the moment once the bike gets over 75-80C, the idle starts to get a bit jumpy, and when I rev the bike slowly, between 2k-3.5k it misfires quite noticably. And power delivery can be quite sluggish, almost as if it is running way too rich. Once it gets to about 4000rpm it runs fine. I've recently changed the spark plugs, cleaned the air filter and ran a batch of injector cleaner through the tank (<- the injector cleaner made it run really bad actually). At the moment I'm not getting any ECU error codes.

    I'm not really sure if this is the same issue with new symptoms or if it is completely unrelated:
    About 2 years ago the bike had a problem that caused it to misfire and cut out after 5000rpm when accelerating heavily. It gave an error code indicating that the Air Intake Temp (AIT) sensor was faulty. I checked it with a multimeter and it tested fine, but I replaced it anyway. I also tested the wiring to it and that was fine as well.

    After replacing the AIT sensor the problem persisted and I kept getting the same error code. After getting the bike checked by a EFI specialist, they still couldnt find the problem. But eventually the problem just resolved itself. Since then I have only had the bike misfire once or twice when accelerating heavily, and it is usually in very hot temps and after about 1 hour + of riding time.

    The bike is a '99 VFR800, done about 75,000km. It has a Power Commander 2 and runs on a downloaded 'best fit' map from the PC website. Also has a staintune can only, and a K&N air filter. It seems to run best on 91RON fuel, 95 and 98RON fuels make it run like shit, with very poor ecconomy and performance, as well as spluttering and misfiring. I've tried running the bike on the factory ECU but the same problems persist.

    I'm wondering if anyone else has had any similar experiences and what they've done to fix them?

    I'll be keeping the bike for another year before I go overseas so I may invest in getting the PC2 tuned properly on a dyno if that is likely to fix the problem but I'm not really 100% sure that it will.

    Thanks in advance.
     
  2. steven113

    steven113 New Member

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    Have you tried disconecting the pc2?
     
  3. RockVFR

    RockVFR New Member

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    Yup :tongue:
     
  4. matt1986vf500f

    matt1986vf500f New Member

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    i dont know anything about these bikes but have you checked the coil for voltage see if its dropping off when it gets hot?
     
  5. dizzy

    dizzy New Member

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    Kinda sounds like an ignition coil, wire, resistor cap...maybe a poor connection between these or on the primary side of the coil...maybe even a pulse generator. Find your test points and check cold resistance, then get your bike hot to fail and restest...look for a big difference in one of the readings.
     
  6. RockVFR

    RockVFR New Member

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    Haven't tested the coils, but that gives me a starting point, I'll start with the easiest/cheapest stuff first.

    Here's an update.

    Hey guys, for the past few days the bike has been running perfectly to and from work, this just highlights the intermitent nature of the problem, sometimes its good, other times its bad.

    But last night when I started it, it began running rough (probably a better description as I don't really think its a true 'misfire' as if one cylinder isn't firing) straight away. I had the choke on at about 2000rpm and it just kept fluctuating between 3k and 1.5k. One thing to point out is I could actually hear a very fast 'clicking' noise, like the sound a BBQ ignition switch makes when you open the gas valve, coming from the left (when sitting on the bike) rear cylinder, each time the idle would drop off. It was loud enough to hear from a few meters away from the bike, even over the sound of the exhaust. I assume it was the sound of the spark plug firing, but I just thought that was really odd.

    When the bike was about 45C I shut the choke off and started riding, and it was idling really bad and very sluggish until just over 3000rpm. Now here's another weird thing, I was almost home, and the temp was about 77C when out of no where the bike just starts running smoothly again like there's nothing wrong.

    What the hell did Honda do to give these bikes such annoying problems!
     
  7. IA-Mike

    IA-Mike New Member

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    If you can hear clicking you may have a spark escaping and going to ground. Run it in the dark and see if you can see it.
     
  8. RockVFR

    RockVFR New Member

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    That would be interesting. What would be the likely cause and remedy for that?

    In all the time I've had the bike I've never heard the clicking noise before and I'm pretty tuned into how the bike sounds and usually pick up any odd noises going on.
     
  9. Maggot

    Maggot New Member

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    I agree with Iowa Mike. Check the spark plug wires at night. You may have an arcing wire that is very close to a ground source. Heating and cooling may cause this wire to get slightly closer or farther away from the ground. If you find the arc you can fix it with heat shrink or electrical tape. See if a spark plug wire isn't too close to an exhaust pipe.
     
  10. RockVFR

    RockVFR New Member

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    I haven't had a chance to do any work on the bike yet but the problem has changed somewhat. Heat no longer seems to be a factor. The misfire seems to be a lot more predominant and it occurs right from when I start the bike, and does not rectify itself as it warms up. (Speaking of, the previous owner replaced the R/R about 20,000km ago, just before I bought it), where as it used to only occur when the bike gets hot.

    It also backfires a bit now. In about 5 hours if riding over the weekend I probably heard a really loud backfire a 3 or 4 times. And although rare, I've had the bike almost cut out completely a couple of times, like I watched the tacho needle drop from 5rpm down to 2rpm and back up a few times while taking off from the lights.

    Apart from that, the problem is still occurring only between idle at 1.5rpm to 3rpm.

    Since Thursday I've ridden in a handful of times and I keep hearing this clicking noise, it is definitely coming from the left rear cylinder (not sure what number this is off hand), and I can't hear it from any other cylider. As I said in the above post, I can only hear the clicking noise as the misfiring/spluttering happens.
     
  11. IA-Mike

    IA-Mike New Member

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    I had a car do that once where the coil tower had cracked. It got so bad that it did it all the time. I fixed it temporarily by taping up the crack.
    I could hear clicking and the engine would miss terribly. In the dark I could see it sparking to ground.
     
  12. RockVFR

    RockVFR New Member

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    I was just thinking, if it is the coil, wouldn't the problem get worse at faster engine speeds not better?

    I mean, the coil may be a secondary problem and I'll check that out, but it seems more a fuel management problem with things only going wrong inside the 1000-3000rpm band, and occasionally at ~5000rpm.
     
  13. CandyRedRC46

    CandyRedRC46 Member

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    +1
    hearing a clicking noise that directly coincides with engine cuttout seems to be a telltale sign of the spark shorting out somewhere other than the spark plug. you may have a spark plug wire rubbing on the frame or on the exhaust. you deffinetely need to run it in the dark and check, before trying anything else...
     
    Last edited: Sep 20, 2009
  14. TAGLICIOUS

    TAGLICIOUS New Member

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    wow I posted for valves before I read your last post... definately sounds electrical. does the fuel pump need replaced? post when you find the issue...
     
  15. weasel

    weasel New Member

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    Don't know if yours has this problem but after buying, I rode my used '99 back home from Cal. A month later I checked the plugs and all the plugs were off their seats, like they weren't torqued correctly when installed.

    Also found 3 header connections that needed to be snugged up.

    My bike showed no signs of anything being wrong tho, but all that stuff
    should be checked occasionally.
     
  16. RockVFR

    RockVFR New Member

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    Ok I found the source of the clicking noise, it is definitely spark arching, so thanks all who suggested it, and it seems to be coming from the left rear spark plug cap and grounding to the cam cover, I could see it in low light.

    So my question is how do I fix this? just buy a new plug lead and cap?

    weasel, the bike has always been well looked after, I replaced the plugs about 2 months ago myself and tightened them up good.
     
  17. RockVFR

    RockVFR New Member

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    Just had a thought, I recently took the bike to a self serve car wash and gave it a good scrub. When I was rinsing it I tried my best not to spray directly towards any openings or gaps where the engine is exposed but I couldnt help some water making contact, especially through the gap between the tank and the metalic frame where you can see the cam rear bank cam cover. I know most bikes are very water resistant by design but could this cause problems...considering this was over two weeks ago now and should have well and truely dried out?
     
  18. dizzy

    dizzy New Member

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    You can probably replace the resistor cap separately. ANY wet connection can cause a problem...it should have dried by now but wet can also accelerate corrosion. However, in your first post you noted you've had problems a couple years now...so it's probably just a coincidence...or it was failing anyway and the water just made it more obvious.

    probably wouldn't be a bad idea to replace at least that cylinder's spark plug as well. With all the arcing going on it could've easily fouled it.
     
  19. CandyRedRC46

    CandyRedRC46 Member

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  20. RockVFR

    RockVFR New Member

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    Hey guys, the ride to work this morning was like a ride through heaven, at idle the needle sat on 1.300rpm like it was stuck on with glue, and the bike responded without hesitation right through the rev range.

    Last night I inspected the spark plug cap and at first couldn see anything, but when I flexed it I could see the tiniest hairline spit in the rubber casing on the side that sits facing the engine. It looked like someone had firmly scraped across it with a very thin razor blade, hardly visible. I have temporarily fixed it just be squeezing the split together and it seems to be holding up. I'll still replace the cap obviously but as these things seem to have horrendously long order delays from Honda it will do in the meantime. But yeh, this morning the bike rode like a dream.

    I'd say what was originally happening was the slit would open up when the rubber gets hot and flexible, exposing just enough wire to make the spark jump intermitently, also being affected by bumps in the road surface etc.

    This still leaves the AIT sensor issue unaccounted for, but we'll just call than an x-file until it happens again.
     
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