Just after take-off with 115% throttle we experienced a reduction in rpm to around 4200 (but manifold pressure was still 40”) then a couple of cycles of a brief recovery followed by the rpm settling at ~4200. The aircraft did not get above 200ft but managed to land back OK.
We did an in-depth visual inspection and checked the compressions which were good and spark plugs looked normal.
We then did a full power ground run with a laptop running the TLR software and observed the rpm slowly dropping to 4600, but MP still 40”. We repeated the test several times, but the issue did not recur. The extract from the attached TCU logs shows the TCU did not think the throttle moved (so position sensor OK) and the airbox temp, airbox pressure, ambient pressure & servo position remained more or less constant, so it doesn’t look like the power reduction was commanded by the TCU.
We suspected a fuel problem so replaced the fuel filter and the fuel hoses downstream of the pumps which were due their 5 year replacement. The engine ran fine after this for 35hours so we thought we'd fixed it and then the same thing happened again :-(
Any suggestions as to where to look next ?
Thanks, Mark
