Dear Abby,
I've been chasing this problem for 4 months now. My RPMs are hunting. At idle, in cruise...basically any time the engine is running, the RPMs are hunting. The problem presents itself as such: It will basically stay where it's supposed to (i.e. 2350) for a moment, then it usually surges up, sometimes 100 RPMs before the prop governor corrects for it, then the problem resolves and the RPMs go lower than my 2350, then the governor corrects for it again. Rinse/repeat.
800 SMOH
In troubleshooting I've done this:
* Sent the MT Governor out for overhaul.
* I have a Lycoming test plate for the governor attach point on the engine. Oil pressure at the main bearing is steady at 80. The prop when using differential pressure tester, injecting air, moves smoothly stop to stop. When we used air to set a random pitch, it seemingly holds it without bleeding down.
* Ran the engine without the governor (it's now a fixed pitch prop right?). Still hunting.
* Removed/Cleaned injectors. They sparkle. I even put them back in.
* Checked for induction air leaks at the cylinders and where the induction tubes mate to the oil sump. No blue. All hoses and bolts are fine. Bolt torques are still spot-on.
* Does it on L/R/both mags. Mag timing is spot on. (Left Mag is a Surefly E-mag).
* I have 12 Iridium Plugs. Starts like a late model car.
* Does it when the electric fuel pump is on/off. Does not make any difference.
* Manifold pressure behaves normal
* CHTs don't seem beyond the ordinary. EGTs expectedly move +/- a few degrees...b/c the engine is surging.
* I've explained this to a few Hartzell prop shops and they ALL insist that the prop is not the root cause in this case. I feel safe with this consensus to look elsewhere...
Where do I go next? Fuel servo/Flow divider?
Mechanical Fuel pump?
Blinker fluid?
I'm starting to feel that this experience is going to make me the master someday, but for now, I'm the pupil and I'm ready to take notes. Any takers?
Thanks in advance.
Signed,
Frustrated in Massachusetts
I've been chasing this problem for 4 months now. My RPMs are hunting. At idle, in cruise...basically any time the engine is running, the RPMs are hunting. The problem presents itself as such: It will basically stay where it's supposed to (i.e. 2350) for a moment, then it usually surges up, sometimes 100 RPMs before the prop governor corrects for it, then the problem resolves and the RPMs go lower than my 2350, then the governor corrects for it again. Rinse/repeat.
800 SMOH
In troubleshooting I've done this:
* Sent the MT Governor out for overhaul.
* I have a Lycoming test plate for the governor attach point on the engine. Oil pressure at the main bearing is steady at 80. The prop when using differential pressure tester, injecting air, moves smoothly stop to stop. When we used air to set a random pitch, it seemingly holds it without bleeding down.
* Ran the engine without the governor (it's now a fixed pitch prop right?). Still hunting.
* Removed/Cleaned injectors. They sparkle. I even put them back in.
* Checked for induction air leaks at the cylinders and where the induction tubes mate to the oil sump. No blue. All hoses and bolts are fine. Bolt torques are still spot-on.
* Does it on L/R/both mags. Mag timing is spot on. (Left Mag is a Surefly E-mag).
* I have 12 Iridium Plugs. Starts like a late model car.
* Does it when the electric fuel pump is on/off. Does not make any difference.
* Manifold pressure behaves normal
* CHTs don't seem beyond the ordinary. EGTs expectedly move +/- a few degrees...b/c the engine is surging.
* I've explained this to a few Hartzell prop shops and they ALL insist that the prop is not the root cause in this case. I feel safe with this consensus to look elsewhere...
Where do I go next? Fuel servo/Flow divider?
Mechanical Fuel pump?
Blinker fluid?
I'm starting to feel that this experience is going to make me the master someday, but for now, I'm the pupil and I'm ready to take notes. Any takers?
Thanks in advance.
Signed,
Frustrated in Massachusetts