Turbocharger Saab 900 I

DESCRIPTION

Vehicles use a Garrett T3 Turbocharger. Exhaust gases drive the turbine, which turns the compressor, pushing air under pressure to the throttle valve.

Excessive pressures are controlled by a boost pressure control valve or wastegate. A pressure switch prevents engine damage in case of wastegate failure. Additional engine protection is provided by the Automatic Performance Control (APC) system. The APC system senses engine knock and automatically cuts back the amount of boost.

The system is designed to operate at low engine speeds, providing increased torque at typical vehicle driving speeds. The turbine shaft is mounted in a floating, sliding-contact bearing having a high oil flow. The shaft actually floats on oil during operation.

Lubrication is supplied by the engine lubrication system. The shaft is sealed against bearing housings with sealing rings installed in shaft grooves.

OPERATION

As engine operation begins, exhaust gases flow through the turbocharger's turbine impeller, causing it to rotate. Gases are expelled through the turbine to the exhaust pipe. As the turbine spins, its shaft turns the compressor impeller, compressing the intake air.

At idle speeds the air compression has little effect upon its operation. However, as engine speed is increased (partial load), the pressurized air enters the system faster, and exhaust gases are expelled faster. The more exhaust gases passing over the turbine impeller, the faster it turns, and the more pressurized air is delivered to the engine.

At full load, the throttle valve is fully open and charge pressure increases. At 8.7-10.1 psi (.61-.71 kg/cm 2 ), the valve in the charge pressure regulator opens, permitting exhaust gases to flow directly to the exhaust pipe, bypassing the turbine impeller.

In the event the valve sticks open, charge pressure increases to 13.1-14.5 psi (.92-1.02 kg/cm 2 ). This causes a pressure switch to break current flow to the fuel pump, thereby preventing engine damage. Pressure switch is located on the turn signal flasher bracket under the instrument panel.

AUTOMATIC PERFORMANCE CONTROL (APC)

Automatic Performance Control (APC) adjusts boost pressure constantly to match octane rating and engine load conditions. Maximum engine output is always available and damage due to pre-ignition (pinging) is eliminated. System consists of knock detector, pressure transducer, solenoid valve, and Electronic Control Unit (ECU).

Knock detector (below intake manifold) senses "pinging" in engine and transmits signals to ECU. Pressure transducer (under dash at left of steering column) senses boost pressure in intake manifold downstream of throttle valve. Pressure is converted to electrical signal which is sent to ECU.

The ECU (under rear seat cushion) also receives RPM signal from ignition system. ECU operates solenoid valve by regulating electrical current pulse ratio. Solenoid valve (right radiator support bracket) governs control pressure to boost pressure regulator. Boost pressure regulator operates boost pressure regulator valve (wastegate) based upon intake pressure.

Solenoid valve is fed by intake pressure downstream from turbocharger. Solenoid inlet tube "C" has fixed diameter orifice. When the solenoid valve is fully shut, wastegate is open fully and provides low boost since boost pressure regulator receives full intake pressure from outlet "W" of solenoid.

When solenoid valve is fully open, pressure is vented through outlet "R" of solenoid to intake upstream from turbocharger. Boost regulator pressure is reduced allowing wastegate to close and increase boost pressure.

Solenoid valve fluctuates between open and closed positions at fixed frequency of 12 Hz. Pulse width changes when boost pressure exceeds 6 psi (.4 kg/cm 2 ). Pulse width is ratio of time solenoid valve is open to time solenoid is closed during each cycle. Solenoid valve cycles 12 times per second. Pulse width is changed by ECU, depending upon signals sent to ECU.

Turbo APC System. Scheme 16

Basic Setting

1. Boost pressure regulator valve and diaphragm unit assembly should be connected to turbocharger. Press regulator valve control lever to "shut" position. Adjust end piece on diaphragm unit push rod so it can easily be fitted to control lever stud, without forcing diaphragm return spring.
2. Screw end piece 3.5 turns inward onto diaphragm unit push rod. Tighten lock nut. Pull out push rod and hook end piece onto lever stud and fit circlip. Check basic setting of boost pressure regulator by road testing car and measuring basic setting pressure while in motion.
3. When basic pressure setting falls within specified tolerances regulator valve lever stud should be sealed with a tamper-proof seal.

Road Testing

1. Run hose of pressure gauge (83 93 514) from passenger compartment to engine compartment. Position pressure checking gauge vertically. Connect hose of pressure gauge to connection of vacuum hoses placed beside expansion tank. Disconnect APC system by detaching electrical wiring from solenoid valve. CAUTION: Checking maximum boost pressure in a road test must be performed as quickly as possible (approximately 3-5 seconds) to avoid abnormally high temperatures building up in brake linings.
2. On cars with manual transmissions, start test by driving car in 3rd gear at an engine speed lower than 1500 RPM. On cars with automatic transmissions, start test by driving car with gear selector in position "1" at an engine speed lower than 1500 RPM.
3. Depress accelerator pedal to floor. When engine speed approaches 3000 RPM, apply brakes with accelerator pedal pressed to floor. Read boost pressure from gauge with engine held under full load at 3000 RPM. NOTE: A boost pressure surge may be noted when engine is accelerated to maximum, i.e. boost pressure will momentarily exceed preset maximum figure when accelerator is floored.
4. Once stabilized, pressure reading should be .3 Bar. Basic pressure setting is only initial setting for function of APC system and has no direct effect on maximum boost pressure level. Engine output is not increased by raising basic boost pressure above .3 Bar.
5. If basic pressure setting falls outside tolerance, adjust boost pressure regulator basic pressure. If basic pressure setting falls within specified tolerances regulator valve lever stud should be sealed with a tamper-proof seal. Reconnect wiring to solenoid valve. Remove pressure reading equipment.
6. Car should be driven at least 1/2 of a mile between each test and after testing is completed in order to allow brake linings to cool.

MAXIMUM BOOST PRESSURE

1. Run hose of Pressure Reading Equipment (83 93 514) from drivers seat to engine compartment. Position pressure checking gauge vertically. Connect hose of pressure reading equipment to connection of vacuum hoses placed beside expansion tank.
2. Tilt rear seat cushion forward and detach electrical wiring from control unit. Connect test wiring harness (83 93 548) with service box between normal harness connector for control unit and control unit itself.
3. Set knock detector switch on service box to "OFF" position. This switching off has to be made to prevent knock detector from varying boost while measurements are being taken. Depending on type of fuel in tank, engine may knock continually while measurements are being taken. Engine should be at normal operating temperature. CAUTION: Test must be performed as quickly as possible to avoid high temperature build-up in brake linings.
4. On cars with manual transmissions, start test by driving car in 3rd gear at an engine speed lower than 1500 RPM. On cars with automatic transmissions, start test by driving car with gear selector in position "1" at an engine speed lower than 1500 RPM.
5. Depress accelerator pedal to floor. When engine speed approaches 3000 RPM, apply brakes so engine is held under full load at 3000 RPM. Read boost pressure from pressure gauge.
6. Once stabilized, pressure reading should be .6 Bar. If boost pressure is correct, remove testing equipment. If boost pressure is incorrect, faulty boost pressure regulator valve, sticking diaphragm push rod bushing, or blocked orifice in solenoid valve hose connection to turbocharger may be the problem.

KNOCK CONTROL

1. Connect Test Wiring Harness (83 93 548) with service box. Set knock detector switch on service box to "ON". Road test at 3000 RPM. If system is working correctly engine boost pressure should drop by about .1 Bar when knocking occurs as a result of engine being put under load at full acceleration.
2. If knocking persists, pressure will be further reduced by system in several steps, until engine runs without knocking. If engine is maintained under full load, boost pressure will try to increase in steps (.1 Bar in 3 seconds) toward nominal figure until knocking occurs again. Boost will once again drop.
3. The lower the octane rating of fuel used in engine, the lower mean figure of boost pressure that engine works with when operating at full acceleration. Each time knock detector is activated, reading on boost pressure gauge will alter boost reading and will drop below preset maximum figure while at the same time flashing red light on test wiring harness service box.
4. Should fuel in tank be of such high octane that knocking does not occur, pressure control is not required. This test procedure should only be used if it is not possible to make engine knock using fuel already in tank.
5. Remove vacuum hose from vacuum control unit on distributor. Seal by connecting hose to drain tap on thermostat housing. This disconnects distributor advance and retard mechanism with the result that engine runs 5° advanced under full load conditions.
6. If necessary, a further method of provoking engine knocking is to disconnect full load enrichment by disconnecting insulated cable terminal at throttle microswitch. Depressing accelerator to floor during road test will now normally cause engine to knock and function of APC system can be observed.
7. If knocking still does not occur, fuel of a lower octane rating must be used in order to carry out this test. Remove test equipment. Reconnect vacuum hose to distributor and disconnected cable to throttle switch on completion of test.

PRESSURE SWITCH

1. Start engine and run at idle. Disconnect hose from pressure switch at intake manifold. Connect pressure gauge and pump (cooling system tester) to pressure switch hose.
2. Increase pressure with pump and check pressure at which engine cuts out. Reading should be 13.1-14.5 psi (.92-1.02 kg/cm 2 ). If not, replace pressure switch.

Note. To avoid damage to transducer connector, apply rest prods on the same side that ohmmeter cables enter connector.

PRESSURE TRANSDUCER

1. Remove transducer electrical connector cover. Using an ohmmeter, measure resistance between terminal No. 23 (Black/White) and terminal No. 10 (Green/Red).
2. Connect air pump via hose and connector to hose from pressure transducer. Disconnect electrical wires from pressure transducer. Connect an ohmmeter to electrical terminals of pressure switch. Resistance should be 10 ohms at atmospheric pressure.
3. Using air pump, raise pressure to approximately 1 Bar, then reduce to .6 Bar while tapping pressure transducer lightly with handle of a screwdriver. Resistance should be 88 ohms at .6 Bar. If readings are not obtained, replace pressure transducer.

SOLENOID VALVE

1. Remove electrical connector on solenoid valve. Disconnect hose running between turbocharger inlet and "R" connection on solenoid valve at compressor inlet end. Connect jumper wires between battery and electrical terminals of solenoid valve.
2. Solenoid valve should be open when current is on and closed when current is off. This can be checked by blowing through disconnected hose. If solenoid valve does not function properly, it should be replaced.
3. In solenoid valve connection marked "C" leading to hose from turbocharger outlet there is an orifice which should have a diameter of .10 (2.5 mm). Check that orifice is free from dirt. If orifice is blocked and dirt cannot be removed, replace solenoid valve.

BOOST PRESSURE

To adjust boost pressure, remove wire seal and circlip from regulator control arm and detach diaphragm lever. Loosen lock nut on lever and rotate lever end in appropriate direction. See CHARGE PRESSURE ADJUSTMENT chart.

Adjusting Charge Pressure Regulator. Scheme 17

CHARGE PRESSURE ADJUSTMENT

Removal

1. Disconnect negative battery cable. Remove air intake and pressure connections from compressor. Loosen pre-heating hose. Remove exhaust elbow between exhaust manifold and compressor.
2. Disconnect oil supply and return lines at turbocharger. Remove bolts securing turbocharger to exhaust manifold and remove turbocharger. Plug all holes in turbocharger.

Installation

1. Attach turbocharger to intake manifold, using new gasket. Attach oil return pipe to turbocharger, using new gasket.
2. Fill oil feed channel with engine oil and attach oil pressure pipe, using new gasket. Install exhaust elbow and exhaust manifold. Install air intake and pressure connections to compressor.
3. On Hall Effect ignition systems, disconnect wiring from control unit before cranking. Crank starter for approximately 30 seconds so turbocharger is primed with oil before engine operation.