Base Engine Misfire with Abnormal Valve Train Noise
| Cause | Correction |
|---|---|
| Worn or loose rocker arms | Repair or replace the valve rocker arms, as required. |
| Worn or bent push rods | Replace the push rods. |
| Sticking valves Carbon buildup on the valve stem and/or seat can cause the valve to not close properly. | Repair or replace, as required. |
| Excessively worn or mis-aligned timing chain | Repair or replace the timing chain, camshaft retainer, and sprockets, as required. |
| Worn camshaft lobes | Replace the camshaft and valve lifters. |
| Sticking lifters | Replace, as required. |
Base Engine Misfire with Abnormal Valve Train Noise
Engine Noise on Start-Up, but Only Lasting a Few Seconds
| Cause | Correction |
|---|---|
| Incorrect oil level An oil level that is overfull causes aeration within the oil. | Add or remove oil, as required, to achieve the proper level. |
| 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 valve lifters, as required. |
| Worn crankshaft thrust bearing | Inspect 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 |
|---|---|
| Plugged oil filter | Replace the oil filter. |
| Low oil pressure | Verify proper oil level. 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 stud, nut, or bolt. Repair or replace, as required. |
| Worn valve rocker arm | Replace the valve rocker arm. |
| Worn pushrod guide plate | Replace, 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 |
| 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 The engine block oil galleries |
| Broken valve spring | Replace the valve spring. |
| Worn and/or damaged valve rotators | Replace the valve rotators, as required. |
| Worn or dirty valve lifters | Replace the valve lifters. |
| Stretched or broken timing chain and/or damaged sprocket teeth | Replace the timing chain and sprockets. |
| Worn camshaft lobes | Inspect the camshaft lobes. Replace the camshaft and valve lifters, as required. |
| Worn valve guides or valve stems | Inspect the valves and valve guides. Repair, as required |
| Stuck valves Carbon on the valve stem or valve seat may cause the valve to stick. | Inspect the valves and valve guides. Repair, as required Use GM top engine cleaner GM P/N 1050002, (Canadian P/N 992872) to eliminate carbon deposits following manufacturers instructions |
Upper Engine Noise, Regardless of Engine Speed
Lower Engine Noise, Regardless of Engine Speed
| Cause | Correction |
|---|---|
| Low oil pressure | Verify proper oil level. 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 . |
| Loose torque converter bolts - automatic transmission only | Inspect the torque converter bolts and flywheel. Repair or replace, as required. |
| Loose or damaged flywheel | Repair or replace the flywheel. |
| Damaged oil pan contacting the oil pump screen An oil pan that has been damaged may improperly position the oil pump screen, preventing proper oil flow to the oil pump. | Inspect the oil pan. Inspect the oil pump screen. Repair or replace, as required. |
| 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, piston pin, and connecting rod. Repair or replace, as required. |
| Excessive connecting rod bearing clearance | Inspect the following components: The connecting rod bearings The connecting rods The crankshaft The crankshaft journals Repair, as required. |
| Excessive crankshaft bearing clearance | Inspect the crankshaft bearings and crankshaft journals. Repair, as required. |
| 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. 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 . |
| Loose torque converter bolts or improperly installed torque converter - automatic transmission only | Inspect the torque converter bolts and flywheel. Verify correct installation of the torque converter. 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: The connecting rod bearings The connecting rods The crankshaft Repair, as required. |
| Excessive crankshaft bearing clearance | Inspect the following components: The crankshaft bearings The crankshaft journals The cylinder block crankshaft bearing bore Repair, as required |
Engine Noise Under Load