Turbocharging system problems usually show up as inadequate boost pressure (lack of. engine power), leaking shaft seals (oil consumption), damaged turbine or compressor wheels (vibration and noise), or excessive boost (detonation). Refer to a vehicle service manual for a detailed troubleshooting chart if needed. It will list the common troubles for the particular turbo system. To protect a turbocharger from damage, some automakers recommend that the oil in a turbocharged engine be changed more frequently. The turbo bearings and shaft, because of the high rotating speeds, are very sensitive to oil contaminants. Engine oil must be kept clean to assure long turbocharger life
Checking turbocharging system
There are several checks that can be made to determine turbo-charging system condition. These include:
- Check connection of all vacuum lines to waste gate and oil lines to turbo, Fig. 22-25.
- Use a regulated, low-pressure air hose to check for waste gate diaphragm leakage and operation.
- Use the dash gauge or a test gauge to measure boost pressure (pressure developed by turbo under a load). If needed, connect the pressure gauge to an intake manifold fitting. Compare to specs.
- Use a stethoscope to listen to bad turbocharger bearings.
To check the internal condition of a turbo, remove the unit from the engine, as in Fig. 22-26. Unbolt the connections at the turbo. Remove the oil lines and take the unit to your workbench. Inspect the turbocharger wheels for physical damage. The slightest knick or dent will throw the unit out of balance, causing vibration. Fig. 22-27 shows how to measure turbo bearing and shaft wear.
WARNING! Never use a hard metal object or sandpaper to remove carbon deposits from the turbine wheel. If you gouge or remove metal, the wheel can vibrate and destroy the turbo. Only use a soft wire brush and solvent to clean the turbo wheels
Installing new turbocharger
Many turbocharger problems are NOT repaired in the field, Fig. 22-28. Most mechanics install a new or, the rebuilt unit. When installing a turbo, you should:
- Make sure the new turbo is the correct type. Compare part numbers.
- Use new gaskets and seals.
- Torque all fasteners to specs.
- If needed, change engine oil and flush oil lines before starting engine.
- If the failure was oil related, check oil supply pressure in feed line to turbo.
Waste gate service
An inoperative waste gate can either cause too much or too little boost pressure. If stuck open, the turbo will not produce boost pressure and the engine will lack power. If stuck closed, detonation and engine damage can result from excessive boost.
Before condemning the waste gate, always check rings, other parts. Check the knock sensor (spark retard system if used) and the ignition timing. Make sure the vacuum-pressure lines are all connected properly. Follow service manual instructions when testing or replacing a waste gate. As shown in Fig. 22-29, waste gate removal is simple. Unbolt the fasteners. Remove the lines and lift the unit off of the engine. Many manuals recommend waste gate renewal, rather than repairs.
Fig. 22-30 shows a turbocharged engine. Can you identify all of the parts? Trace flow of fuel charge into engine and exhaust out of engine.