Base Engine Misfire with Abnormal Valve Train Noise
| Cause | Correction |
|---|---|
| Worn or loose rocker arms The rocker arm bearing end caps and/or needle bearings should be intact within the rocker arm assembly. | Replace the valve rocker arms as required. |
| Worn or bent pushrods | Replace the pushrods. Inspect the top of the pistons for valve contact. If the top of the piston shows valve contact, replace the piston and pin assembly. |
| Stuck valves Carbon buildup on the valve stem can cause the valve not to close properly. | Repair or replace as required. |
| Excessively worn or mis-aligned timing chain | Replace the timing chain and sprockets as required. |
| Worn camshaft lobes | Replace the camshaft and valve lifters. |
| Sticking lifters | Replace as required. |
| Improper operation of the Displacement-on-Demand (DOD) system | Repair as required. Refer to Displacement on Demand (DOD) System Diagnosis . |
| Cut or damaged oil pump screen O-ring seal which may cause aeration of the engine oil | Repair as required. Refer to Oil Pressure Diagnosis and Testing . |
Base Engine Misfire with Abnormal Valve Train Noise
Engine Noise on Start-Up, but Only Lasting a Few Seconds
| Cause | Correction |
|---|---|
| Incorrect oil filter without anti-drainback feature | Install the correct oil filter. |
| Incorrect oil viscosity | Drain the oil. Install the correct viscosity oil. |
| High valve lifter leak down rate | Replace the lifters as required. |
| Worn crankshaft thrust bearing | Check the crankshaft end play. Inspect the thrust bearing and crankshaft. Repair or replace as required. |
| Damaged or faulty oil filter bypass valve | Inspect the oil filter bypass valve for proper operation. Repair or replace as required. |
Engine Noise on Start-Up, but Only Lasting a Few Seconds
Upper Engine Noise, Regardless of Engine Speed
| Cause | Correction |
|---|---|
| Low oil pressure | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing . Repair or replace as required. |
| Loose and/or worn valve rocker arm attachments | Inspect the valve rocker arm, bolt, and pedestal. Repair or replace as required. |
| Worn or damaged valve rocker arm | Inspect the rocker arm for wear or missing needle bearings Replace the valve rocker arms as required. |
| Bent or damaged push rod | Inspect the following components and replace as required: The valve rocker arm The valve push rod The valve lifter The valve lifter guide The piston Inspect the top of the pistons for valve contact. If the top of the piston shows valve contact, replace the piston and pin assembly. |
| Improper lubrication to the valve rocker arms | Inspect the following components and repair or replace as required: The valve rocker arm The valve push rod The valve lifter The oil filter bypass valve The oil pump and pump screen Improper operation of the Displacement-on-Demand (DOD) oil pressure relief valve The engine block oil galleries |
| Broken valve spring | Replace the valve spring and spring shim. |
| Worn or dirty valve lifters | Replace the valve lifters. |
| DOD valve lifter with a broken spring | Replace as required. |
| Stretched or broken timing chain and/or damaged sprocket teeth | Replace the timing chain and sprockets. |
| Worn engine camshaft lobes | Inspect the engine camshaft lobes. Replace the camshaft and valve lifters as required. |
| Worn valve guides or valve stems | Inspect the following components and repair as required: The valves The valve guides |
| Stuck valves Carbon on the valve stem or valve seat may cause the valve to stay open. | Inspect the following components and repair as required: The valves The valve guides |
| Cut or damaged oil pump screen O-ring seal which may cause aeration of the engine oil | Repair as required. Refer to Oil Pressure Diagnosis and Testing . |
Upper Engine Noise, Regardless of Engine Speed
Lower Engine Noise, Regardless of Engine Speed
| Cause | Correction |
|---|---|
| Low oil pressure | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing . Repair or replace damaged components as required. |
| Worn accessory drive components Abnormalities such as severe cracking, bumps or missing areas in the accessory drive belt and/or misalignment of system components. | Inspect the accessory drive system. Repair or replace as required. |
| Loose or damaged crankshaft balancer | Inspect the crankshaft balancer. Repair or replace as required. |
| Detonation or spark knock | Verify the correct operation of the ignition controls system. Refer to Detonation/Spark Knock in Engine Controls - 5.3L. |
| Loose torque converter bolts | Inspect the torque converter bolts and flywheel. Repair or replace as required. |
| Loose or damaged flywheel | Repair or replace the flywheel. |
| Oil pump screen loose, damaged or restricted | Inspect the oil pump screen. Repair or replace as required. |
| Excessive piston-to-cylinder bore clearance | Inspect the piston and cylinder bore. Repair as required. |
| Excessive piston pin-to-bore clearance | Inspect the piston, pin, and connecting rod. Replace the piston and pin as an assembly, as required. |
| Excessive connecting rod bearing clearance | Inspect the following components, and repair as required: The connecting rod bearings The connecting rods The crankshaft The crankshaft journals |
| Excessive crankshaft bearing clearance | Inspect the following components, and repair as required: The crankshaft bearings The crankshaft journals |
| Incorrect piston, piston pin and connecting rod installation Pistons must be installed with the mark or dimple on the top of the piston facing the front of the engine. Piston pins must be centered in the connecting rod pin bore. | Verify the pistons, piston pins and connecting rods are installed correctly. Refer to Piston, Connecting Rod, and Bearing Installation . Repair as required. |
Lower Engine Noise, Regardless of Engine Speed
Engine Noise Under Load
| Cause | Correction |
|---|---|
| Low oil pressure | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing . Repair or replace as required. |
| Detonation or spark knock | Verify the correct operation of the ignition controls. Refer to Detonation/Spark Knock in Engine Controls - 5.3L. |
| Loose torque converter bolts | Inspect the torque converter bolts and flywheel. Repair as required. |
| Cracked flywheel - automatic transmission | Inspect the flywheel bolts and flywheel. Repair as required. |
| Excessive connecting rod bearing clearance | Inspect the following components, and repair as required: The connecting rod bearings The connecting rods The crankshaft |
| Excessive crankshaft bearing clearance | Inspect the following components, and repair as required: The crankshaft bearings The crankshaft journals The cylinder block crankshaft bearing bore |
Engine Noise Under Load