GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1996 🢒 Chevy Suburban - 4WD 🢒 Engine 🢒 Engine Mechanical - 7.4L 🢒 Engine Knock Diagnosis

Knocks Cold and Continues for 2 to 3 Minutes
    • Engine flywheel contacting the splash shield. Reposition the splash shield.
    • Loose or broken crankshaft balancer or drive pulleys. Tighten or replace as necessary.
    • Excessive piston to bore clearance. Replace the piston.
    • Cold engine knock usually disappears when the specific cylinder secondary ignition circuit is grounded out. Cold engine piston knock which disappears in 1.5 minutes should be considered acceptable.
    • Bent connecting rod.

Heavy Knock with Torque Applied
    • Broken Balancer or pulley hub. Replace parts as necessary.
    • Loose torque converter bolts.
    • Accessory belts too tight or nicked. Replace and/or tension to specifications as necessary.
    • Flywheel cracked.
    • Excessive main bearing clearance. Replace as necessary.
    • Excessive rod bearing clearance. Replace as necessary.

Light Knock Hot
    • Detonation or spark knock. Check operation of EST or ESC. Refer to Engine Controls.
    • Loose torque converter bolts.
    • Exhaust leak at the manifold. Tighten the bolts and/or replace the gasket.
    • Excessive rod bearing clearance. Replace bearings as necessary.

Knocks on Start-Up but Only Lasts a Few Seconds

The following conditions may produce engine knocks on initial start-up, but only last a few seconds:

    • Improper oil viscosity.
       - Install proper oil viscosity for expected temperatures.
       - Refer to SECTION 0B.
    • Hydraulic lifter bleed down
       - Clean, test and replace hydraulic lifter, as necessary.
       - When the engine is off, some valves will open. Spring pressure against the lifters will tend to bleed the lifter down. Repair the lifter only if the problem is consistent.
       - Engines operated for only short periods between start-ups may have lifter noise that lasts for a few minutes. This is a normal condition.
    • Excessive crankshaft end clearance; Replace the crankshaft thrust bearing.
    • Excessive front main bearing clearance; Replace the worn parts.
    • Timing chain tensioner malfunction; Clean, inspect and replace the timing chain tensioner, if required.

Knocks at Idle Hot
    • Inspect the drive belt for wear. Check the tension and/or replace as necessary.
    • Inspect the A/C compressor or generator bearing. Replace or repair as necessary.
    • Inspect the valve train. Replace the parts as necessary.
    • Inspect for improper oil viscosity. Install proper viscosity oil for expected temperature. Refer to SECTION 0B for engine oil specifications.
    • Inspect for excessive piston pin clearance. Replace the piston and pin as necessary.
    • Inspect the connecting rod alignment. Check and replace the rods as necessary.
    • Inspect for insufficient piston to bore clearance. Hone the bore and fit the new piston.
    • Inspect the crankshaft balancer for looseness. Torque and/or replace the worn parts.
    • Ensure that the piston pin is not offset to the wrong side. Install the correct piston.