1999 VFR with a wierd issue ???

Hi guys Its been awhile since the last conversation.  Yet this time it is a crazy one, I''ll do my best to keep it condensed.  Last year I got my hands on a very clean low millage VFR that I knew of from a gentlemen that took care of it it was very well less the last couple years where he hadn't time for riding so it sat.  Next he decided to sell the beast again I knew what this one was about so made him an offer thinking its going to need the basics to get it down the road.  He was getting ready to fire it up and get back into it, but things went in a different direction.  then I didn't hear back for a few moths then here he was coming full circle and took my offer  Nice 😉 so I thought.

Ok, here we go once it was in my garage the normal fluid changes,  plus battery and the complete going over al look good  Now it time take it for a spin fired right off so typical Honda  😉 then once out it acted like it was down on power compared to my 98,  Then bing GOat  2800 rpms it took off, all was good.... hahah   Nope, any time you go below 2800, it kinda goes flat so back to the shop I went.  Knowing these critters like i do and know this particular VFR told me since it sat for awhile it could be a fuel injector so into the gunnels we go,  while it was opened up, I swapped outall  4 them , button up,  lets try this again. PUFF!!  only to have the same result. Head -a -scratching  had me use a temp gun on the exhausts, yep Number 4 was the culprit, not firing off util the 2800 mark. So the next was done one at a time.

Fuel pump, check pressure checked out  along with new fuel filter, check,  still does it

ECU swap  still does it

ignition coils with leads and boot along with new plugs.. still does it

FPR swap.. still does it.

Here's the weird part, it starts and idles great hard tell its not running on all four, I even did the starter vale alignment, it still does the same after 2800 it's great. I decided to let it act this way for a couple tanks, no change.  

Next I modded out the air box so I could get it running less air box to check injectors with a tester of sorts ,that told me as best one could, $#@! those bugger are buried. that they are working, Yet ??? 

So I got a syringe and squirted fuel in # 4 while running.  Wa-La  the exhaust temp showed up, so yea its not getting fuel in there below 2800 Hmm?

A double checking that the fuel lines are good,which they are, so now the question is,  is it the Injector wire harness? or maybe there's a pulse input thing with the injector mode that isn't working?  if so where ?

 Thanks for the Listening,  If this VFR wasn't so sharp, I'd part it all out.

I may be wrong but believe the pulse generator is a single device on the clutch cover i.e. it services all 4 cylinders, so I think you'd rule that out. 

You've eliminated the ignition so yes that leaves fuel, which you showed to fix the issue. I believe you can get a plug-in test light that is in series with the injector and would show if there is a pulse below 2800 rpm, someone with an osciliscope can probably check that more easily and determine if the injector pulse is generated by the ECU. A bit of dodgy wiring certainly sounds plausible. Good luck. 

Yes, they are called NOID lights. You plug them into the wiring harness and fire up the bike and if the injector is getting signal, it will flash. Not sure if the Honda's switch ground or power, but I'm sure someone here can tell you. Also not sure if these bikes are batch fire, or sequential.

You could also unplug the injector and the ECU and test the continuity of the wire(s), and also check for a short to ground. I don't have the manual for that bike, but I think you can download them from this forum.

Good luck with finding that gremlin!

Thanks for the Noid thing.   That gets me thinking if a digital multi meter may work.  Now I'm gong to throw on a an extra injector to see how it actually acts.  😉 

I'm not aware of any switch over point around 2800 rpm. You can test the Fi easily if you can rig up a spare injector with a basic fluid feed don't use fuel. Just wire it up point it in a bucket & see if it fires at idle &/or up to 2800rpm. If not & ECU is known good, then has to be a signal loss, but that would normally cover all rpms. 

Yes that's whats throwing me for a loop. Unless.. it's like what I have seen and heard of like when a coil lead is lose or barely on where as the rpms increase so does the the energy. In this case as the rpms rise the voltage gets to a point where it can jump the connection.  But in this case I'm pretty sure the 12v with the injector is a constant and not a lot needed in a amp load here, which begs the question of,  WT......     😉 Yep, I'm going to do that as I just happen to have 4 extra Injectors laying around, just ordered up a little fuel pump, so we will see what comes of that.

Up date: after a bit of fiddling I was able to hook up a separate fuel pump & fuel lines to the injector in question on #4 and had it wired in to the VFRs circuit. Once running I turn on the fuel pump and, Wa-la there is a nice spray of fuel. The only thing puzzling me left to do now is pull the fuel rail out to see whats going on.  How odd, could it be, all though the fuel pump test showed me 70 psi,  that's not enough?  When running above 2800 it makes more psi? The Shop manual says the injectors need or run at 43 psi.  I would think if it runs great above 2800,  it shoud be working fine below 2800.. Totally Weird.  At least this test takes away the VFRs FI circuitry.

UP Date:  Wow!  What a Go figure.   It turns out I had a partly like a very little lack of communication with the ECU via the TPS being it was only the very first part of the throttle not telling the ECU what to do with the #4 injector.   Doh!, it was telling me it was working, yet only partly I found out.   Anywho, all is like it should be.  Runs great now,  but what a headscratcher.                                                                                                                                                                                                                                                                                            Side note:  if anyone is looking for a very sharp 5th-generation low miles, very well taken care of with nice options. I should have this one available sooner than later. Though I am in the PNW of the USA,  so there's that hurdle.

That's great, but...   what WAS IT tho?  Corrosion?  Bad sensor?