RPM 's Bounce

[JimT]

I think I've seen the same or similar issue with my cm2250. If I have the engine up over 1400rpm then let it drop back to idle it will bounce a couple times when it gets down to the set idle rpm. It's not massive, sometimes only about +/-10rpm. And if I wind the engine down while still in gear then go back to neutral when it's close to the set idle it doesn't do it. Not sure exactly when this started, but I think it was present before my inframe. My first thought was maybe a leaky injector. I've done cylinder cut-out test, injector performance test, rail pressure test and everything was perfect. Only thing I haven't done is pull out and try individually testing each injector.

I'm not sure exactly what or why, but at 1400rpm I can hear a difference in the fueling. Quieter below 1400, louder (more horse power or torque? or just a different fueling pattern?) at 1400 and up. Been that way since the programming was done last February. Related or not, recently I've noticed that the line isn't so clear cut sometimes. Sometimes it will kick in at a lower rpm or continue down to a lower rpm instead of the strict above or below 1400rpm point. Seems more likely to do this when it's still cold, though it still occurs when warm.

I bring that second symptom up because I think it goes hand in hand with the first and further points to an injector not acting right or being slow to respond, despite not being able to narrow it down during tests.