The 1-2K RPM miss has been driving me bonkers. It's enough to piss off the Pope! Last night I spent some more time diagnosing it, and like usual I learned a few things, and ended up with more questions than answers.
Here is why it runs rough at 1-2K RPMs. The computer is adding extra injection pulses like it is accelerating.
The computer normally adds extra injection pulses when extreme enrichment is needed, like when the throttle is opening. Only between these RPMs do I get extra injection pulses like this. As soon as the engine hits 2000 RPMs, it disappears. Anytime I've ever seen anything like this on a car the first thing I suspected was a bad TPS. Rapid fluctuations in TPS voltage, even small ones, can result in a whole lot of extra fuel getting added. It's not that it can't be anything else, it's just that the TPS is the number one suspect. It was adjusted within specs but I decided to fool with it, trying several different closed throttle voltages. Every time I moved it, the RPM where it missed changed. Furthermore, if I substituted the signal with my signal generator, the problem disappeared.
Here is what the TPS looked like on the scope.
It's pretty easy to see that it drops to 0V for a tiny slice of time. Less than 300 microseconds, in fact. I figured there was NO WAY the primitive processor in the FJR could see this spike, but I couldn't find any other reasons for the false enrichment. I scoped MAP, Crank/Cam, and came up empty handed. Before spending $200+ on a TPS I ran the bike with the TPS unplugged, and the PCII accelerator pump turned on, and way up. Aside from the Engine Light being on it ran pretty darn good, aside from the surge that the PCIII fixed. I rode 40 miles of mixed riding looking for the problem to come back, but it didn't. I was convinved I needed a TPS. I put one on, and the bike ran no better than the original one. Anyone wanna buy a nice, low mileage TPS?
So here is where we are: The PCM is adding tons of enrichment only between 1-2K RPMs. I can't find any input other than TPS that is acting incorrectly. A new TPS doesn't fix it, but substituting a known good signal does. It just doesn't make any sense.
At this point I'm really wishing I had another bike to throw the scope on. In the mean time I may check to see if I can get the bike to go into closed loop without a TPS input. I'll unplug the wire from the PCM so the PCIII can still operate normally and see what happens. If anyone has any suggestions I'd glady consider them.
Joe