1999 VFR800 Unsolved Misfiring Problem

good to hear you got this worked out!:thumbsup:

 

Hey guys,
I replaced the plug cap on the weekend and the bike is running great now. It has no idling issues and runs really smooth. I did however rev the bike up very slowly to see if there were any problem areas and if I hold the revs at about 4000rpm, the needle does gently move around like it can't quite find where it should be. It's nothing like it used to be, but it is still noticeable compared to the rest of the rev range. It only seems to be an issue when free reving, it doesn't have any noticeable effect when riding, so unless it worsens and becomes a problem, I'm pretty happy to live with it, unless someone can suggest an easy fix of course.

 

You can buy (solid wire core, not resistance wire) sparkplug wire cut to length from bulk roll at a good old-school autoparts store for pennies.......no need to order from Honda.

Yamaha dealers a sell a high quality plug wire cut to whatever length you need, runs about $2/foot.

 

Ten years is a long time for the rubber to last in that harsh enviornment. I generally change out plug wires on vehicles before that.

I was riding in Colorado a few years ago during their 'monsoon' season. It just poured several times a day. My bike was cutting out during hard acceleration but I just thought that it was the altitude. When it persisted back on the plains I realized that I had a problem. When I pulled the plug boots there was a black soot on the porcelain from the arcing. Cleaned it up and the bike ran fine afterwards. I now use a grease on the plugs to keep the moisture out. I also use an electrical grease on all my electrical connectors to keep corrosion out of them.
I'm glad that you were able to find your problem.

 

It happened again! But I think I know where to start looking now.

Well today the temp reached a steamy 40 degrees. The bike started up normally and was running normally until I had to sit in some gridlock traffic and the bike started to get hot. It got up to 95C when I took off through an intersection and it just started running like an angry dog, spluttering, misfiring, jolting, etc. The tacho needle was bouncing up and down like crazy. I had to pick some stuff up on my way home from work so I kept riding for a bit and the bike just kept misbehaving. On throttle, off throttle, high revs, low revs, it was just going berserk no matter what I did. Anyway, I gave the bike a big rev and hit red-line and the FI light lit up while the bike was still running. I pulled into a car park and sat there, but it didn't blink. I shut it off and the light went out. I took the key out and started again, started it up and the light didn't come back on.

So I went and picked up my stuff, long enough for the bike to cool down to about 88C. The bike was running fine again. I still had about 10 mins to ride home, so I watched the temp gauge, when it got to about 100C it started playing up again, but not quite as severely this time and the FI light still wouldn't come back on. I pulled into my driveway and again gave the bike a hard rev, hitting red-line and the light came on again! So I wheeled it into the car spot sat there and watched and this time it started flashing. 1 long flash (this = 10 I understand, please correct me if I am wrong?) and 9 short flashes. So the answer is 42! I mean 19.

The Ignition Pulse Generator according to The Book. Now I'm a little embarrassed to admit this but in my defense, someone told me this is how it works. Last time I saw an error code for this problem, I interpreted it to mean 9 flashes, as you are supposed to exclude the long flash, so I was stumped when I went to replace the IAT sensor and the FI light still said there was something wrong with it!

So, now I will start looking at the Pulse Generator, however I can't find any indication to it in the Service Manual, perhaps someone could point me in the right direction? (I admit I am tired and cranky after work so I didn't have a thorough check.)

And can anyone suggest what I should do to check it/fix it?

Thanks,

I HOPE SO MUCH THAT THIS WILL FIX THE DAMN PROBLEM FINALLY!!!!

 

Pulse generator is under clutch cover, but you need only find the wires coming out and test resistance in ohms according to service manual specifications.

It's typical for failing pulse generators to work OK when cool but fail after engine has reached operating temperature, then work again after bike has cooled.

In your situation you'd only detect a fault while engine is in highest heat zone.

One ignition coil-- whichever one sends signals to operate the tach--should also be considered a suspect.

 

Thanks heaps for that, I'll check it out. As for the coil, how do I determine which coil operates the tacho?

 

Service manual wiring diagram......or someone on here that knows.

 

Old old thread, but I could have written it myself, having very similar problems, recently fitted new plugs, now I need to get new plug caps to see if that will solve it.

 

caps can be tested for proper resistance as outlined in fsm.

 

I don't have a fsm I'm looking through the Haynes manual here, it's not much help. The op had a problem with the cap.

 

you can download your fsm free here. you really may not need the caps, and u could test by hooking wire directly to plug.

 

Where would I find it here to download?

 

sorrry, i've no clue, but someone knows. you could try @ vfrd.

watching your bike run in the dark (pull out headlight fuse) will often show bad wires or caps spaRKING TO GROUND.

 

I can just switch the headlights off, are yours always on?

 

yes, always on for government-mandated safety.

 

Here's a link to the manual at the "other" VFR site.

https://www.vfrdiscussion.com/index...onda-vfr-service-manual-optimized-bookmarked/

 

That's the way now on newer bikes in the EU, my 5th gen has a light switch on the right side, high beams and flash button on the left side.
I'll try and download that fsm, thanks guys, thinking of buying a complete set of coils and plug caps from ebay, and just swap all over and see what happens, 2nd hand set so not too expensive. I might be able to swap them over myself, any testing or stuff like that I'd have to take her to a proper mechanic.

 

oh, no, not that !!

you can get alot more help here than you have already. for example, have you checked plug colors after a run ? checked wire and cap resistances ? inspected air filter ?

try to figure out whether misfire happens on only one cylinder or at random on any. are you certain the plugs are the proper ones for the engine ? is it more likely when engine is hot or cold ?

could possibly be a ecu error.

 

Plugs are new and correct, air filter? that's also new anyway, I wouldn't know how to check resistance in a plug cap, I will investigate further soon.