thefleshrocket Posted April 14, 2020 Share Posted April 14, 2020 My '99 has ~25K miles on it. Last fall, before I put it away, it misfired on me a couple of times shortly after starting up the bike. I looked up the code and it was for the MAP sensor. I bought a used replacement on Ebay (for a 6th gen as it looked "clean" and supposedly it's the same sensor because Honda used it on a bunch of bikes) and installed it. Speaking of which, one screw, one wiring harness, and one vacuum hose.. easy, right? Well, whatever nincompoop decided that the one screw should be on the edge of the airbox facing down with almost no room to get to it without removing the airbox should be punched. It could have easily been secured several other ways with no drawbacks, but no.. took me close to an hour to get the old sensor unscrewed and the new one installed using a right-angle screwdriver. Ugh. Should have just pulled the airbox but didn't want to add any other variables to the equation. Anyway, I fired up the bike and did a 60-mile ride, mostly at high speed (100-125mph cruising speeds.. on an, um, privately owned road), and the bike ran flawlessly. The next day, the battery was dead (I still have to troubleshoot but I suspect one leg of the stator isn't working consistently), but I got it jumpstarted and rode home. The misfire from the past Fall was back. Oddly, it only happened between 4500-6000RPM--if I rode a gear or two low when cruising to keep the RPM up over 6000, or when I was at a slow area and the RPM was under 4K, there were no misfires. But man, get it in the 5-5500 "sweet" spot and it would misfire periodically. When I say misfire, it's like the entire engine cut out for a split second, then came back immediately. Not a miss on one cylinder, but all four of them shutting down very briefly. The FI light would come on for the duration of the misfire and maybe a half second after. I posit that I didn't get any misfires on the initial ride because the RPM was well over 6000 for almost the entire time, aside from initial startup and the first few warmup miles. And I confirmed that there is a stored code for the MAP sensor, so it's not something else that's angry. I realize it's possible that the replacement MAP sensor was also bad, but that seems like a stretch. I could buy another one (and not mount it to the airbox unless the bike runs perfectly) to test it out, but what else should I be looking into if it's not the MAP sensor itself? Thanks! Link to comment Share on other sites More sharing options...
thefleshrocket Posted April 14, 2020 Author Share Posted April 14, 2020 Not sure how to turn on notifications, and I missed the "notify me of replies" button in my original post, but now it's turned on. Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 14, 2020 Member Contributer Share Posted April 14, 2020 Get your battery and charging system sorted first. Then clear any stored Fi codes, see how you go after that. Link to comment Share on other sites More sharing options...
GreginDenver Posted April 14, 2020 Share Posted April 14, 2020 I'm with Grum on this one. It sounds like your bike's charging system is failing. The Regulator/Rectifier on the 5th Gen is a known fail point (it's an old-school Shunt-type Regulator/Rectifier, this type of R/R doesn't last forever, heat issues caused by the shunt-to-ground method of its rectification function eventually kill it). Sometimes the R/R failure is precipitated by corrosion in the multi-plug that connects it to the lines from the alternator stator (this can lead to high temperatures in the plug which will result in a burned/melted appearance). Occasionally it's the stator itself that fails. Either way the R/R ends up compromised and now it won't be able to maintain your battery, which is why it fails during rides. The MAP sensor problem could easily be nothing more than a by-product of worsening situation with your battery and R/R. So, yes, Grum is pointing you in the right direction: Trace the bike's charging wiring looking for connectors that are corroded or have a "burned/partly melted" appearance. If you don't find anything like that you should test the R/R (there are plenty of YouTube videos that can run you through how to do this). Bear in mind that by now your bike's battery may be in poor condition (possibly in need of replacement) you can take it to a shop and have it tested to see if it can still deliver AMPs. It might be that your battery needs to be replaced. It might be that both your battery and your R/R need to be replaced. That's a start... Link to comment Share on other sites More sharing options...
thefleshrocket Posted April 19, 2020 Author Share Posted April 19, 2020 Ok, I’ll look at the charging system. I’m 95% sure I put a Rick’s R/R on it a couple thousand miles ago (6 or 7 years ago as the bike sat it pieces in my basement for a long time) and the battery is a several-year-old EarthX LiFePo4 that didn’t have enough CCA to spin my 1125R’s starter but easily cranks the VFR. But I know I haven’t touched the stator. And the fact that charging voltage is sometimes in the mid 14s and other times in the low 13s or upper 12s makes me think one leg of the stator is iffy. So I’ll start by attacking that and leave the MAP sensor alone for the time being. Thanks’ Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted April 19, 2020 Member Contributer Share Posted April 19, 2020 I also agree with Grum because we have been here before... Start with the battery for it's the weakest link in the whole system... To determine the condition of an Maintenance Free battery give it a refreshing charge... wait 30 minutes... measure terminal voltage... 12.8 or higher is a good battery... 12.0 to 12.8 is a insufficient charge... recharge... 12.0 or lower... battery unserviceable... Lithium batteries terminal voltage are different than lead acid... understanding the charger operation is key to success... 14.340 100% 13.300 90% 13.270 80% 13.160 70% 13.130 60% 13.116 50% 13.104 40% 12.996 30% 12.866 20% 12.730 10% 9.200 0% I'd would not begin troubleshooting unless the battery's starting voltage is greater than 13 volts and the charging system is steady at the prescribe 14.0 to 14.8 @ 5,000 rpm because it is the logical component to your intermittent problem... at this junction I think we can say that the new part failed to fix the root problem... Inspect all connections for corrosion and resistance... because a corroded electric connection is known to prevent the full transfer of volts to the point of cutting out... My own RC45 QD quick disconnect fried and almost to turn my bike into a crispy critter... Link to comment Share on other sites More sharing options...
thefleshrocket Posted May 8, 2020 Author Share Posted May 8, 2020 So, it was the battery. I replaced the EarthX LiFePo4 with a known good conventional battery, and have put 400 trouble free miles on the bike since. Thanks to everyone for your input! Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted May 8, 2020 Member Contributer Share Posted May 8, 2020 46 minutes ago, thefleshrocket said: So, it was the battery. I replaced the EarthX LiFePo4 with a known good conventional battery, and have put 400 trouble free miles on the bike since. Thanks to everyone for your input! That's good news. After 400 miles of riding it sounds like your charging system must be OK, have you checked your charging voltage anyway? Link to comment Share on other sites More sharing options...
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