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!
