DESCRIPTION
Most models use a water-cooled turbocharger, mounted directly to the exhaust manifold with a wastegate assembly attached to rear of turbine housing. The turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate. Other components include impellers, impeller shaft, bearings and impeller housings.
The safety valve of the system is a pressure actuated wastegate that prevents excessive intake boost pressure.
Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to the system.
OPERATION
At idle and light throttle, the Turbo engine operates like a standard engine. When more power is required, exhaust gases from exhaust manifold enter the turbocharger's turbine housing and flow through the turbine blades.
Exhaust flow and turbine speed increase as throttle opens and RPM increases. The impeller turns with turbine and forces air into compressor housing and intake manifold. As impeller and turbine speed increases, boost pressure also increases.
If boost pressure exceeds safe limits, engine damage may result. The wastegate opens when exhaust pressure exceeds a predetermined limit and allows exhaust gases to by-pass compressor.
When Starting
After engine has started, allow it to run at idle for several minutes. If engine has been shut down for a long period, be sure to run engine at idle until engine oil has circulated throughout engine. When turbocharger is replaced, remove oil pipe by loosening top flare nut and pour fresh engine oil directly into oil filler port.
During Operation
Monitor oil pressure gauge to confirm that constant oil pressure is available. If abnormal noise is produced by rotating parts of turbocharger, or unusual vibration is noted, stop operation and check.
When Stopping
Allow engine to run at idle for several minutes before stopping engine. If engine is operated at high load, then stopped abruptly, the engine oil supply is cut off while the turbocharger is still very hot. The turbocharger bearings will be overheated and could be damaged.
TESTING
Note. No tests are available for Mazda.
TROUBLE SHOOTING
Note. Check the following items. If found defective, replace turbocharger assembly. If related parts are defective, repair or replace.
VIBRATION OR NOISE
- Inspect for defective bearings or interference of rotating parts with related objects. Consider neglect of engine oil change, sustained use with contamination in oil pipe, a restricted or broken oil filter. Check for repeated abrupt starts and stops that could cause bearing failure.
- If nothing is wrong with lubricating system, an incorrectly balanced rotating section or bent shaft may be suspected. This is due to excessive wear of bearings or contamination that have caused damage to turbine or compressor wheels.
- If any of these conditions exist, turbocharger assembly must be replaced. Before a new turbocharger assembly is installed, carefully check for contamination or pieces of broken turbine or compressor wheels which might be left in manifold system.
LOW BOOST PRESSURE
- Check air cleaner element for contamination or clogging and clean or replace element as necessary. If turbine or compressor wheels do not rotate smoothly and lightly when turned by hand, replace turbocharger assembly. Check wastegate valve or relief valve which might be left opened.
- If turbocharger appears to be good, but has low boost pressure, check for the following: Gas leaks in exhaust system. Deformed or clogged exhaust pipe or muffler which might be causing increased exhaust resistance. Air leaks from compressor discharge side.
WHITE EXHAUST SMOKE
Sustained engine operation with faulty bearings will result in failure of oil seal which could cause leakage of engine oil into exhaust and intake pipes. Leakage of engine oil from turbocharger into exhaust pipe or intake pipe will result in White colored exhaust. If this occurs, check for clogged, crushed or deformed oil return pipe. If nothing is wrong with oil return pipe, leakage is probably due to wear of piston ring (seal ring) in turbocharger.
Removal (MX-6 & 626)
- Drain engine coolant. Remove air hoses and air by-pass valve. Remove turbocharger heat insulators. Remove oil pipes from turbocharger. Remove coolant hoses, EGR pipe and oxygen sensor.
- Loosen bolts securing turbocharger to bracket. Remove nuts attaching exhaust pipe to turbocharger. Remove nuts attaching turbocharger to exhaust manifold. Remove turbocharger.
Scheme 76
Removal (323)
- Remove engine undercover. Drain engine coolant. Remove radiator. Remove intake air pipe and intake air hoses.
- Remove turbocharger heat insulators. Remove coolant hoses from turbocharger. Remove oil pipes from turbocharger.
- Loosen bolts securing turbocharger to bracket. Remove nuts attaching exhaust pipe to turbocharger. Remove nuts attaching turbocharger to exhaust manifold. Remove turbocharger.
Scheme 77
Removal (RX7)
Disconnect air hoses and air pump. Remove air funnel and air hose. Remove air control valve. Remove split air pipe. Disconnect water hose and water pipe. Disconnect oil pipes. Remove insulator covers. Disconnect front converter. Remove turbocharger and insulator covers. Remove exhaust manifold and actuator.
Installation (All Models)
To install, reverse removal procedure. Replace gasket between turbocharger and exhaust manifold. Before installation, add 25 cc of clean engine oil to oil passage of turbocharger.