As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING SCHEDULED FLIGHT AFTER TAKEOFF CLIMB AT 700 MSL, THE REAR ENGINE STARTED DECREASING RPM'S, AND INCREASING MANIFOLD ON REAR ENGINE. VIBRATION FELT ON AIRCRAFT RETURN AND LANDING WITHOUT ANY FURTHER INCIDENT. REAR ENGINE RUN-UP AND FOUND DEFECTIVE MECHANICAL FUEL PUMP. REPLACED BY NEW ONE. ENGINE RUN-UP AND FOUND AIRWORTHY. THE AIRCRAFT WAS RETURNED TO SERVICE.