TROUBLESHOOTING 11-6 Symptoms Possible causes Low power output Abnormal engine noise Remarks Incorrect oil viscosity Gr 11 Incorrect/defective fuel Gr 13 Incorrect valve clearance Defective cylinder head gasket Worn valve/valve seat, and carbon deposits Weakened valve spring Worn/damaged piston ring(s) Worn/damaged piston ring groove(s) Incorrect injection timing Gr 13 Defective injection pump Gr 13 Defective cooling system Gr 14 Defective injection nozzle(s) Gr 13 Air trapped in fuel system Gr 13 Clogged air cleaner Gr 15 Clogged muffler Gr 15 Defective turbocharger Gr 15 Incorrectly fitted pipe(s)/hose(s) Gr 13 Injection pump, alternator, or other auxiliary device(s) defective/incorrectly fitted Gr 13, 54 Loose/damaged V-belt Gr 14 Incorrectly fitted crankshaft pulley Defective air cleaner or muffler Gr 15 Defective valve spring(s) Defective rocker shaft and bracket Incorrect lubrication of rocker shaft bracket Incorrect backlash in timing gears Incorrect lubrication of timing gear peripheries and idler shafts Worn connecting rod small end bushing and piston pin Worn/damaged crankshaft pin and connecting rod big end bearing Worn/damaged crankshaft journal and main bearing Excessive end play in crankshaft and camshaft Worn tappet(s) and camshaft