DESCRIPTION
Vehicles use a turbocharger, mounted directly to front of exhaust manifold. A wastegate is attached to rear of exhaust manifold. Other system components include an additional safety switch to prevent excessive boost, oil cooler mounted behind the front spoiler, injector cooling thermoswitch, intercooler, dual oil filters, and an oil thermostat.
Engine modifications include a piston cooling system (oil jet spray), low compression pistons, larger piston pins, sodium-filled exhaust valves, and increased oil capacity.
Scheme 48
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. A boost pressure safety switch is used for protection in case wastegate fails. This switch is connected to the intake manifold and serves as ground for electric fuel pump. When pressure is higher than 11.6 psi (.82 kg/cm 2 ), the switch opens and the fuel pump stops, slowing the engine.
An electric blower fan is used to cool the injectors and intake manifold and prevent vapor lock. A thermal switch controls fan operation and turns the fan on whenever manifold temperatures exceed 212°F (100°C).
Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Turbo models have increased oil capacity, an oil cooler, oil thermostat, and special filter. Both turbocharger filter and regular engine filter should be changed at regular intervals.
BOOST PRESSURE
| CAUTION | This operation requires the use of a chassis dynamometer to safely test components. If dynamometer is not available, testing can simulated with a road test and the correct equipment arrangement. |
- To test turbocharging system, use Pressure Gauge (VW 1397). Gauge is equipped with a valve which locks pressure measurement when closed.
- Attach gauge to vacuum advance at distributor, using "T" fitting supplied with gauge. Ensure vacuum advance unit and charcoal canister purge valve are free of leaks. Use hose clamps at all connections to avoid low readings.
- Warm engine until oil temperature is above 176°F (80°C). Accelerate engine to 4000 RPM in second gear with automatic transmission (third gear on manual transmission). Hold vehicle speed constant and close gauge shut-off valve. Record reading. NOTE: Testing should not exceed 10 seconds at full boost.
- Boost pressure readings will vary with temperature. Compare results with readings in BOOST PRESSURE SPECIFICATIONS table.
- If boost pressure is incorrect, replace wastegate as a testing measure and retest. If boost pressure is still incorrect, replace turbocharger.
| Ambient Temperature | Psi (kg/cm 2 ) |
|---|---|
| 4°F (-20°C) | 6.2-6.9 (.43-.49) |
| 14°F (-10°C) | 6.0-6.8 (.42-.48) |
| 32°F (0°C) | 5.9-6.6 (.41-.47) |
| 50°F (10°C) | 5.7-6.5 (.40-.46) |
| 68°F (20°C) | 5.6-6.3 (.39-.45) |
| 86°F (30°C) | 5.3-6.2 (.37-.44) |
BOOST PRESSURE SPECIFICATIONS
End Play
Attach dial indicator to the turbocharger. (Scheme 49) Zero dial indicator, with 1 mm preload, pointing toward turbocharger shaft. Move shaft backward and forward. Maximum end play should be.008" (.2 mm).
Scheme 49
Side Play
Mount dial indicator with stem on side of turbocharger shaft end nut. Zero dial indicator, with 1 mm preload, pointing toward hub of shaft. Push shaft toward dial indicator and return. Maximum side play should be .022" (.55 mm).
WASTEGATE SOLENOID
- Remove connector from multi-thermo switch and turn ignition on. Energize wastegate solenoid by momentarily brushing lead to wastegate solenoid at multi-thermo switch. Solenoid will click if operating properly.
- Remove connector from wastegate solenoid. Check voltage at connector terminal No. 1 (Green/Purple wire). Voltage should read approximately 12 volts. Turn ignition off and remove connector from electronic control unit.
- Using an ohmmeter, measure resistance between terminal No. 2 (Blue/Black wire) and terminal No. 19. Ohmmeter should read 0 ohms. If not, check for open circuit in wiring or connectors. If circuits are functional, replace wastegate solenoid.
Removal
- Disconnect battery and all air hoses from turbocharger. Unclip air filter cover and remove cover plate.
- Disconnect front exhaust pipe from turbocharger. Place drain pan under turbocharger and disconnect oil supply and return lines from turbocharger.
- Disconnect exhaust pipe from wastegate pipe. Remove alternator and disconnect right engine mount cooling air hose. Remove turbocharger.
Installation
To install, reverse removal procedure.