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Caddyinfo's Cadillac How-To Section

Cadillac Spark Knock Ping

Rough, Unstable, or Incorrect Idle and Stalling

4.9L Engine Knock/Ping Analysis:

Condition Possible Cause Correction
Engine knocks Cold and continues for two to three minutes.  Knock increase with torque. a. flywheel contacting splash shield

b. loose or broken balancer or drive pulleys.

c. Excessive piston to bore clearance.

d. bent connecting rod.

e. Piston 180 degrees off

a. reposition splash shield

b. tighten or replace as necessary.

c. replace piston/liner assembly

d. replace bent connecting

e. rotate piston 180 degrees.

Engine has heavy knock, hot with torque applied a. broken balancer or pulley hub

b. loose torque converter bolts

c. accessory belt too tight or nicked

d. exhaust system grounded.

e. flywheel cracked

f. excessive main bearing clearance

g. excessive rod bearing clearance

a. replace parts as necessary.

b. tighten bolts.

c. replace belt or tensioner as necessary

d. reposition as necessary.

e. replace flywheel

f. replace as necessary

g. replace as necessary

Engine has light knock, hot in light load conditions a. detonation or spark knock

b. loose torque converter bolts

c. exhaust leak at manifold

d. excessive rod bearing clearance

a. see detonation diagnosis section 6e

b. tighten bolts

c. tighten bolts

d. replace bearings as necessary

Engine knocks on initial start up but only lasts a few seconds a. improper oil viscosity

b. hydraulic lifter bleed down

c. excessive crankshaft end clearance

d. excessive main bearing clearance

a. install proper oil viscosity

b. clean, test and replace as necessary

c. replace crankshaft thrust bearing

d. replace worn parts.

Engine knocks at idle hot a. loose or worn drive belt

b. compressor or generator bearing.

c. valve train

d. improper oil viscosity

e. excessive piston pin clearance

f. connecting rod alignment

g. insufficient piston to bore or liner clearance

h. loose crankshaft balancer.

a. replace belt or tensioner as necessary.

b. replace as necessary.

c. see valve train noise diagnosis

d. install proper viscosity oil for expected temperature.

e. replace piston liner/assembly

f. check and replace rods as necessary.

g. replace piston/liner assembly

h. torque any or replace worn parts


Detonation/Spark Knock

DEFINITION:  A mild to severe knock, that usually occurs under acceleration.  The engine produces sharp metallic sounds that change with throttle opening.

  • Check for poor fuel quality, proper octane rating

  • Check for overheating problems:

    • Radiator cap won't hold pressure

    • Low coolant

    • Restricted air or coolant flow to or through radiator

    • inoperative electric cooling fans

  • Check for incorrect PROM

  • Check ignition timing

  • Check EGR operation

  • Check for loose or improperly connected body ground, engine grounds, or distributor ground

  • Perform fuel pressure and injector flow tests

  • Decarbon the engine using top engine cleaner.  follow the instructions on the can.  If top engine cleaner improves or eliminates the condition then check for carbon sticking valves or other flow restricting deposits in the heads.

  • Check for leaking valve seals

  • Check for improper operation of transmission and VCC.

  • Check spark plugs for proper heat range and type.  Improper heat range or type may overheat the plug and cause pre-ignition.

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