Bell 412 unusual engine problem
Hello there. Just picking up our Bell 412 from contractor following a 600 hr inspection. The #1 engine was taken out because it was reported that engine stalling / popping was occurring. Some of the compressor blades were changed out and the engine got a new combustion liner.
We started doing our post 600 hr ground runs and noticed that the #1 engine was still popping since repair! It seemed to pop like a machine gun going off between 61% to 70% Ng (N1) on a normal wind up of the #1 engine throttle. If the pilot wound up the throttle quickly like if we were doing an accel check, it wouldn't pop. Also if he brought up the throttle slowly, it wouldn't happen. It would only happen during a "normal" wind up of the throttle and it didn't matter if the governor was in auto or manual.
So far we have swapped fuel clusters from our #2 side since it was proven serviceable during ground runs, changed bleed valves, fuel surge accumulator, fuel dump valve, checked P3 filter, checked for air leaks, changed the setting on the accel dome 3 clicks in either direction and still has the symptoms!
So any input on the cause of this problem would be very helpful because i think we've changed about everything that we can before we change the engine!
Thanks.