The AFM/POH for the specific airplane contains information that should be followed in the event of any abnormal engine instrument indications. The table shown in Figure offers generic information on some of the more commonly experienced in-flight abnormal engine instrument indications, their possible causes, and corrective actions.

MalfunctionProbable CauseCorrective Action
Loss of rpm during cruise flight (non-altitude engines)Carburetor or induction icing or air filter cloggingApply carburetor heat. If dirty filter is suspected and non-filtered air is available, switch selector to unfiltered position.
Loss of manifold pressure during cruise flightSame as aboveSame as above
Turbocharger failurePossible exhaust leak. Shutdown engine or use lowest practicable power setting. Land as soon as possible.
Gain of manifold pressure during cruise flightThrottle has opened, propeller control has decreased rpm, or improper method of power reductionReadjust throttle and tighten friction lock. Reduce manifold pressure prior to reducing rpm.
High oil temperatureOil congealed in coolerReduce power. Land. Preheat engine
Inadequate engine coolingReduce power. Increase airspeed
Detonation or preignitionObserve cylinder head temperatures for high reading. Reduce manifold pressure. Enrich mixture
Forthcoming internal engine failureLand soon as possible or feather propeller and stop engine.
Defective thermostatic oil cooler controlLand as soon as possible. Consult maintenance personnel.
Low oil temperatureEngine not warmed up to operating temperatureWarm engine in prescribed manner
High oil pressureCold oilSame as above
Possible internal pluggingReduce power. Land as soon as possible
Low oil pressureBroken pressure relief valveLand as soon as possible or feather propeller and stop engine.
Insufficient oilSame as above
Burned out bearingsSame as above
Fluctuating oil pressureLow oil pressure, loose oil lines, defective pressure relief valveSame as above
High cylinder head temperatureImproper cowl flap adjustmentAdjust cowl flaps.
Insufficient airspeed for coolingincrease airspeed.
Improper mixture adjustmentAdjust mixture.
Detonation or preignitionReduce power, enrich mixture, increase cooling airflow.
Low cylinder head temperatureExcessive cowl flap openingAdjust cowl flaps.
Excessively rich mixtureAdjust mixture control
Extended glides without clearing engineClear engine long enough to keep temperatures at minimum range.
Ammeter indicating dischargeAlternator or generator failureShed unnecessary electrical load. Land as soon as practicable.
Load meter indicating zeroSame as aboveSame as above
Surging rpm and overspeedingDefective propellerAdjust propeller rpm
Defective engineConsult maintenance
Defective propeller governorAdjust propeller control. Attempt to restore normal operation
Defective tachometerConsult maintenance
Improper mixture settingReadjust mixture for smooth operation
Loss of airspeed in cruise flight with manifold pressure and rpm constantPossible loss of one or more cylindersLand soon as possible
Rough running engineImproper mixture control settingAdjust mixture for smooth operation
Defective ignition or valveConsult maintenance personnel
Detonation or preignitionReduce power, enrich mixture, open cowl flaps to reduce cylinder head temp. Land as soon as possible
Induction air leakReduce power, Consult maintenance
Plugged fuel nozzle (fuel injection)Same as above
Excessive fuel pressure or fuel flowLean mixture control
Loss of fuel pressureEngine driven pump failure
No fuel
Turn on boost pumps
Switch tanks, turn on fuel
Commonly experienced in-flight abnormal engine instrument indications, their possible causes, and corrective actions