Turbocharger Diagnostics

MasterTech News - April 1999

Turbocharger Failure Diagnosis

To facilitate turbocharger failure diagnosis and avoid possible customer returns, the following procedure is recommended.

   The first step in any diagnosis is to verify the customers concern, and may involve a road test if necessary. Complaints may range from excessive noise to a lack of power or a surge in engine speed, among others.
    Since oil in the air induction system may cause an increase in engine speed, remove the pipe from the air cleaner housing at the turbocharger and inspect for excessive oil in the compressor housing. It's important to note that a slight residue of oil, which is caused by a restriction at the air cleaner element, is normal. If excessive oil is observed, the intercooler and related piping need to be flushed.
    For low power or inordinate noise complaints, pressure test the air induction system at approximately 20 psi -NOTE: DO NOT exceed 30 psi. While the system is pressurized, check for leaks at all the joints with a soap and water mixture. Make any necessary repairs.
    Visually inspect the turbocharger for damage. The compressor wheel should not contact the compressor housing when you apply light pressure to the nose of the compressor wheel. Specifications are .003" to .005" endplay and .0 1 2" to .0 1 8" radial play.
    Then pressure test the wastegate actuator for leaks and proper movement. Be sure that the rubber control hose that connects to the wastegate is properly clamped at both ends and is free of leaks. Refer to TSB 11-08-98 for complete details.

Star Center News - Volume 29, April 1999


Do to the increase in "No Trouble Found" Cummins diesel turbo warranty, this article has been developed to assist technicians in the field in correctly diagnosing turbocharger failures.

The first step in any diagnosis of a turbo is to verify the concern (Noise, lack of power, and/or oil contamination).

Before disassembling the entire induction system, remove the pipe from the air cleaner housing at the turbo and inspect for any oil in the compressor housing of the turbo. A slight residue of oil is normal and is caused by a restriction at the air cleaner element.

NOTE: Oil in the induction system could possibly cause an RPM increase. If the system is contaminated with oil, the intercooler and piping need to be flushed. For a loss of power and/or noise concerns the next step is to pressure test the entire induction system at approx. 20 PSI, and do not exceed 30 PSI for safety purposes. Check the system for air leaks using a soap and water mixture at all joints while the system is pressurized to 20 PSI.

Visually inspect the turbo for any apparent damage. The compressor wheel should not contact the compressor housing while applying light pressure to the nose of the compressor wheel. The specifications are .003" to .005" end play and .012" to .018" radial play.

The next step is to pressure test the waste gate actuator and test for leaks and proper movement. Refer to TSB 11 -08-98. Verify the rubber control hose that connects to the waste gate is properly clamped at both ends and is free of leaks.

Star Center News - Volume 13 date unknown


Some owners of 1994-97 Dodge Ram trucks equipped with the Cummins diesel engine may complain of various types of turbocharger noise. The following noises may be among those :

Remember, what is heard as turbocharger noise may not be caused by a noisy turbocharger. Before replacing a turbocharger perform the following diagnosis.

A.    If a loud whine or whistle is heard during acceleration and increases or decreases with rpm and load. 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.

1.    With the engine running at idle and the transmission in Park or Neutral 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.

2.    Check the exhaust manifold and exhaust system for leaks.

B.    Exhaust howling (Spooky-hoot) during turbo boost conditions.

This condition usually occurs over a narrow speed range and may be caused by a muffler tuning issue. This condition can be diagnosed by wedging a 2x4 wooden block between the frame rail and the flat area in the middle of the muffler. Repeat the conditions at which the noise occurs. This condition cannot be corrected at this time; however a new muffler is being evaluated and is expected to be available in early 1997.

C.    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.

D.    Low boost pressure.

Low boost pressure is usually a symptom of low fuel injection pump fuel delivery and is associated low power complaints. Refer to TSB 18-29-95 for proper diagnosis.

Turbocharger wastegate adjustment should be checked for proper operation. Refer to the applicable model year Dodge Ram Service Manual for proper adjustment procedures.

E.    Other causes of turbocharger failure.

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 steps:

1.    .With the engine off, remove the air, cleaner to turbocharger intake tube.

2.    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.

3.    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.

4.    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.


Last Update: February 22, 2000