Engine Noise
ENGINE NOISE
Special Tools:
Engine Noise Overview
NOTE: When diagnosing engine noise problems, make sure that noises caused by accessories, such as the A/C Compressor and power takeoff, are not mistaken for engine noises. Remove the accessory drive belts to eliminate noise caused by these units. Noise will also travel to other metal parts not related to the problem.
NOTE: The use of a stethoscope can help locate an engine noise.
Engine noises heard that are at Crankshaft speed (engine RPM), are noises related to the Crankshaft, Pistons, Connecting Rods, and piston pins. Noises heard that are at Camshaft speed (one-half of the engine RPM), are related to the valve train. A handheld digital tachometer can help to determine if the noise is related to components operating at crankshaft or camshaft speed. Engine noise can sometimes be isolated by performing a cylinder cutout test. If the volume of the noise decreases or the noise disappears, it is related to that particular engine cylinder. There is not a definite rule or test that will positively determine the source of a noise complaint. Engine driven components and accessories, such as gear-driven fan clutches, hydraulic pumps, belt-driven Alternators, A/C Compressors, and Turbochargers can contribute to engine noise. Use the following information as a guide to diagnosing engine noises.
Main Bearing Noise
The noise caused by a main bearing with excessive clearance is a loud dull knock heard when the engine is under a load. The knock is heard regularly every other revolution. If all of the main bearings have excessive clearance, a loud clatter will be heard. The noise is the loudest when the engine is lugging or under heavy load. The knock is duller than a connecting rod noise. Low oil pressure can also accompany this condition. Look for an oil light on instrument cluster. If the bearing is not loose enough to produce a knock by itself, the bearing can knock if the oil is too thin, or if there is no oil at the bearing. An irregular noise can indicate worn crankshaft thrust bearings. An intermittent sharp knock indicates excessive crankshaft end clearance. Repeated clutch disengagements can cause a change in the noise.
Connecting Rod Bearing Noise
Connecting rods with excessive clearance knock at all engine speeds, and under both idle and load conditions. The knock is usually rhythmic and the speed and volume will increase and decrease relative to engine speed. When the bearings begin to become loose, the noise can sometimes be confused with piston slap or loose piston pins. Low oil pressure can also accompany this condition. Look for an oil light on instrument cluster.
Piston Noise
It can be difficult to tell the difference between a piston pin, connecting rod, or piston noise. A loose piston pin causes a loud double knock which is usually heard when the engine is idling. When the injector to this cylinder is cut out, a noticeable change will be heard in the sound of the knocking noise. On some engines the knock becomes more noticeable when the vehicle is operated on the road at steady speed condition.
Turbocharger
A Turbocharger noise can be identified by one of the following:
1. A loud whine or whistle during acceleration
- This condition is most often the result of a loose clamp/hose at the Turbocharger compressor outlet, charge air cooler (CAC) inlet, CAC outlet or at the Intake Manifold. Some things to look for:
- With the engine running at idle, the Transmission in Park or Neutral, and with the parking brake set, feel for boost air escaping at each connection between the Turbocharger compressor outlet and Intake Manifold. For limited access areas, spray soapy water on those connectors and look for bubbles.
- Check the Exhaust Manifold and exhaust system for leaks.
2. Exhaust howling during turbo boost
- This condition usually occurs over a narrow speed range and may be caused by an issue with the muffler (usually external damage) bent touching frame or bent restricting exhaust flow.
3. Loud popping, whooshing, flushing, fluttering, noise emitted during closed throttle deceleration
- This condition is caused by inability of the engine to intake higher boost levels that are present at the beginning of closed throttle deceleration. Pressure generated by the Turbocharger has nowhere to go, thus causing it to "stall" or "surge". The noise will sound as though it is coming through the air cleaner, however this is a normal condition. No damage will be sustained and the Turbocharger should not be changed for this condition.
4. Low boost pressure
- Low boost pressure is usually a symptom of low fuel injection pump fuel delivery and is associated low power complaints. Generally Turbocharger replacement will be related to turbine shaft failures or Turbocharger housing seal leaks. To check for turbine shaft bearing damage, perform the following checks:
- With the engine off, remove the air cleaner to Turbocharger intake tube.
- Visually inspect the Turbocharger compressor fan. The fan blades should not contact the fan housing and the fan blades should not be chipped, bent or damaged in any way.
- Check the end play of the compressor to fan. A small amount of fore/aft play is normal. Excessive play that would cause fan distortion or fan to housing contact is not acceptable. In this case, replace the Turbocharger.
- While pushing the turbine shaft left, right, up and down, gently rotate the compressor wheel. The compressor fan should turn freely by hand, if it doesn't replace the turbocharger.
Fuel System
A fuel system noise can be identified by one of the following conditions:
1. Loud knock (Rap) type sound with rough idle (vibration and smoke
- This condition can be caused by one of the following:
- Alternative fuel or fuel contamination. Fuel Contamination Perform the DIESEL FUEL CONTAMINATION TEST procedure.
- There may be air in the fuel system. This requires checking and correction.
- Fuel Injection Pump phasing may be incorrect. Check the Fuel Injection Pump phasing if necessary. Installation to find the timing procedure.
- Excessive pressure in the high pressure side of the system. This should be accompanied by a fault.
- The fuel injectors may be stuck or have low opening pressure. This requires replacement of defective injectors. A cylinder cut out test or mechanical blocking of injectors (injector block off (9011)) can be used to identify failed injectors.