Basic Construction and Operation
The turbocharger assembly has a turbine housing, a compressor housing and a bearing housing (refer to Figure 6-4). A turbine wheel/shaft connects to a compressor wheel, and the assembly rotates inside the housings.
Basic turbocharger operation starts with exhaust gases entering the turbine housing, causing the turbine wheel/shaft to rotate (see Figure 6-5). As the exhaust gases spin the turbine wheel/shaft, the compressor wheel spins.
The action of the compressor wheel increases the pressure and flow of the air intake charge and is dependent on exhaust gas flow.
The power of the engine provides exhaust gas pressure needed to take air under atmospheric pressure and provide air under boost pressure in the engine intake manifold. Since exhaust gas pressure varies with engine speed, the amount of boost also varies.
Turbocharger Mounting
The engine supports the turbocharger, using the right exhaust manifold, and studs and nuts secure it (see Figure 6-6). Exhaust gases from both the left and right cylinder heads flow into the turbine housing and the gases exit the turbine housing into the exhaust pipe and muffler.
The compressor housing of the turbocharger has an inlet connected to the air filter assembly. All intake air to the engine flows into and out of the compressor housing.
The turbocharger bearing housing has an oil inlet connected to a supply hose from the engine lubrication system (see Figure 6-7). The oil outlet from the bearing housing has a pipe/hose connecting it to the crankcase part of the cylinder case (see page 3-11 for more information).
A shield mounted on a bracket at the right rocker cover prevents heat produced by the turbocharger from affecting the operation of the fuel injection nozzles for cylinders #4 and #6. The heat shield is secured by slot alignment and two bolts.
Turbocharger Lubrication
Oil entering the bearing housing of the turbocharger travels to two sleeve-type bearings (refer to Figure 6-8). The bearings have clearance in the housing and float in oil during turbocharger operation. The turbine wheel/shaft also floats in oil between it and the bearings.
As oil moves past the bearings and shaft, it travels in a special passage inside the bearing housing near the turbine wheel to cool nearby parts (see Figure 6-9). The oil then exits the bearing housing at an outlet port and travels to the crankcase part of the cylinder case through a drain pipe/hose.
A shield between the turbine and bearing housings reduces the transfer of heat to the lubricating oil. The use of the special cooling passage and heat shield greatly reduces the possibility of oil in the turbocharger overheating and forming carbon deposits (known as coking). No special turbocharger cool-down procedure to prevent coking is required after running the engine.
Turbocharger Bearings and Seals
The sleeve-type bearing at the turbine wheel end of the bearing housing has two retaining rings to keep it in position (refer to Figure 6-10). The sleeve-type bearing at the compressor wheel end of the bearing housing is positioned by a retaining ring and the thrust bushing.
The turbocharger uses a thrust bushing and bearing at the compressor wheel end of the turbine wheel/shaft to control end-play.
Two metal seal rings on the turbine wheel/shaft contact a seal plate assembly to prevent oil from entering the compressor housing (see Figure 6-11). One metal seal ring on the other end of the turbine wheel/shaft contacts the bearing housing bore to prevent oil from entering the turbine housing.
Turbocharger Wastegate Valve and Actuator Assembly
The turbocharger turbine housing has a mechanically operated wastegate valve that allows exhaust gases to bypass the turbine wheel and directly enter the exhaust pipe/muffler (see Figure 6-12). The wastegate valve operates at higher exhaust gas pressures to limit engine power. It acts like a turbine wheel speed governor to limit the maximum amount of boost pressure to 5 psi.
An actuator assembly provides a calibrated spring force to keep the wastegate valve closed, and the pressure of exhaust gases flowing in the turbine housing provides force to open the wastegate valve (see Figure 6-13). The position of the wastegate valve and length of the actuator rod are extremely critical for proper turbocharger operation.
During turbocharger manufacture, the turbine, bearing and compressor housings are aligned so that the positioning of the wastegate valve and actuator assembly provide the specified performance characteristics.
Because of this feature, no realignment of the housings is permitted during service.
Engine/Turbocharger Performance
The 6.5L V8 diesel engine has a turbocharger for several reasons:
• To provide an increase in engine power without adding a substantial increase in weight
• To provide consistent power at all altitudes by compensating for changes in air density
• To increase combustion turbulence and air/fuel mixing efficiency, resulting in greater fuel economy
• To reduce exhaust emissions (especially smoke)
The 6.5L V8 turbo diesel engine provides quick power response at low engine speeds. Under full-load conditions, the engine is capable of steadily increasing its output torque as it accelerates up to approximately 1,700 rpm (refer to Figure 6-14). At this point, the intake manifold has a maximum boost pressure of 5 psi, and the turbocharger compressor wheel speed may reach 80,000 rpm.
Under less than full-load conditions, the turbocharger works with the engine to provide varying levels of power under a broader range of speeds. Intake manifold boost pressure will also vary, and turbocharger compressor wheel speeds can be as low as 15,000 rpm (at idle speed).
As part of diagnosis, a technician may test intake manifold boost pressure in these steps:
1. Follow these safety precautions:
• Use an assistant to stand on either side of the vehicle during the test.
• Block the drive wheels of the vehicle and set the parking brake.
2. Remove the front center mounting bolt of the air inlet duct and replace it with the special boost gauge (see Figure 6-15).
3. Start the engine, place the transmission in OD range, and operate the engine at full-throttle for 10 seconds.
4. Have the assistant observe the boost gauge reading during the test.
Note: A boost test reading above 2 psi indicates that the turbocharger is working properly.
Turbocharger Diagnosis
Turbocharger operation relates to the following diagnosis hints (refer to Figure 6-16 for component identification):
Condition #1: Engine lacks power
Cause:
A. Restricted air filter
B. Obstructed turbocharger inlet duct
C. Air leak in turbocharger inlet or outlet ducts
D. Obstructed intake manifold
E. Air leak in intake manifold/gaskets
F. Restricted exhaust system
G. Exhaust gas leak in manifold
H. Turbocharger turbine wheel/shaft binding due to coking
I. Turbocharger turbine wheel/shaft or compressor wheel unbalanced
J. Internal turbocharger damage
Correction:
A. Replace air filter.
B. Remove obstruction.
C. Secure clamps or replace damaged duct(s).
D. Remove obstruction.
E. Tighten mounting bolts or replace manifold/gaskets.
F. Check exhaust system and replace damaged part(s).
G. Tighten manifold mounting bolts or replace damaged part(s).
H. Replace turbocharger, check oil supply and drain for restrictions, and change engine oil/filter.
I. Replace turbocharger.
J. Replace turbocharger.
Condition #2:
Cause:
Turbocharger noise
A. Restriction or air leak in turbocharger inlet or outlet ducts
B. Turbocharger turbine wheel/shaft or compressor wheel unbalanced
C. Turbocharger turbine wheel/shaft or compressor wheel contacting housing
Correction:
A. Secure clamps or replace damaged duct(s).
B. Replace turbocharger.
C. Locate cause of damage and replace turbocharger.
Condition #3: Black exhaust smoke
Cause: Lack of intake air, causing improper air/fuel ratio
Correction: Refer to corrections for condition #1.
Condition #4: Blue exhaust smoke and abnormal oil consumption
Cause:
A. Lack of intake air
B. Restricted oil drain tube
C. Oil leakage past turbine seal ring
D. Oil leakage past compressor seal rings
Correction:
A. Refer to corrections for condition #1.
B. Clean or replace oil drain tube.
C. Replace turbocharger.
D. Replace turbocharger.
Turbocharger Inspection
As part of diagnosis of the turbocharger, perform the following steps:
1. Listen for the unusual sounds:
– A high-pitched whine that may indicate an air induction or exhaust leak
– A sound that is cycling in pitch that may indicate one of the following faults:
• Blockage in the turbocharger inlet duct
• Restriction in the air filter
• Dirt accumulation on the turbocharger compressor wheel
– A sharp, high-pitched scream that indicates turbocharger bearing wear or turbine/compressor wheel contact with a housing
2. Look at components:
– The compressor wheel blades (inspect for bends, breaks, erosion, cracks or dirt accumulation) – refer to Figure 6-17
– The compressor housing (inspect for signs of contact)
– The bearing housing (inspect for signs of oil leakage)
Note: Oil on the compressor wheel blades may be seen, since the Crankcase Depression Regulator Valve (CDRV) outlet is on the inlet duct to the turbocharger compressor housing.
3. Check internal rotating parts in these steps:
– Rotate the compressor wheel by spinning the nut on the end of the shaft in a clockwise direction (observe signs of binding or housing contact).
– While rotating the compressor wheel, pull and push the shaft nut (observe signs of binding or housing
contact).
– While rotating the compressor wheel, raise and lower the shaft nut slightly (observe signs of binding or housing contact).
Note: If the turbocharger fails any of the above checks, replace it as an assembly. No specifications for runout or end-play are given, due to the design characteristics of the sleeve-type floating bearings.
4. Inspect the wastegate and actuator in the following steps:
– Pull the actuator rod toward the rear of the engine, causing the wastegate valve to open (observe no signs of binding).
– Release the actuator rod (observe that the valve closes under spring tension without binding).
Note: If the actuator does not snap back into a closed position, replace it.
5. Perform the boost pressure test (see page 6-15).
