Hi folks,
A couple of days ago, I flew a short 45-minute practice cross-country with my CFI in a 1979 Mooney m20k 231 (with a Turbo Plus intercooler and Merlin waste gate). We flew at 8,500 and during the flight felt a couple of light kicks or sputters from the engine. The other odd thing was that a VERY small movement of the throttle moved MP from 34 to 25 or so. There was no easy way to keep move the power smoothly through that range. And on final, when I wanted to pull the engine to idle, the MP would not fall below about 19. At the destination airport, the line guy who welcomed us said that the plane sounded weird on approach. When we were ready to head back to our home airport, we pre-flighted the plane and did a run-up VERY carefully, watching everything. Once again, we could not get the MP on the indicator to go below about 18 or 19, but the engine sounded normal / idle with the throttle pulled back. Note that I have two indicators: a JPI engine monitor and a steam gauge, both telling me the same MP numbers. The other notable item was that oil pressure was a bit low (top of the yellow) below 1200 and the temp was close to the top of the green. We decided to take off. On climbout, at 105 MPH (~90 kt) and 34" MP, I normally get ~1,000 ft/minute climb. I was getting between 200 and 300. Note: the airport is just a few feet above sea level, and the day was warm but not hot, so D.A. was not an issue. We made the call to return to the field immediately and landed without incident. Oil was at 6.5 quarts on pre-flight inspection and no oil leaks were visible on post-flight inspection.
We left the plane at the FBO and will have the local A&P look at it this week but meanwhile, I wanted to post this here because it seems like an intriguing mystery and I wonder if we'll solve it here before the A&P does.
Any ideas welcome!