System/component Tests Subaru XT I

INTRODUCTION

Note. Prior to testing separate components or systems, it is highly recommended that all procedures listed in BASIC TESTING be performed. Since many computer controlled and monitored components will set a trouble code if they malfunction, it is also recommended that self diagnosis be performed. See TESTS W/CODES .

HIGH TURBO BOOST PRESSURE

If turbocharger fails, excessive boost pressures can cause engine knock and overheating. Check wastegate operation, electrical circuits between wastegate duty solenoid and ECU and ECU problems.

LOW TURBO BOOST PRESSURE

Low boost pressure can cause the following: lack of power, poor acceleration, and increased fuel consumption. Check for leaks in the intake and exhaust system, incorrect ignition timing, electrical circuits between wastegate duty solenoid and ECU and ECU problems.

OIL LEAKS - TURBOCHARGER

1. Worn turbocharger oil seals can cause excessive oil consumption and White smoke from the exhaust. Remove center exhaust pipe and examine the turbocharger from the exhaust side. If there is excessive carbon deposits on the turbine exhaust side, oil is leaking from the turbine.
2. The turbocharger is not necessarily defective when oil is present on the blower side. Oil most likely has come from oil vapors contained in blow-by gases present in the intake system or defective PCV system.
3. If intake side contains oil and a rattle is present, remove the turbocharger. Check the end play and side play.

COMPONENT TESTING - TURBOCHARGER

Note. No provision has been made for turbocharger disassembly or adjustment. Replace turbocharger if found to be defective.

BOOST PRESSURE

1. Disconnect wastegate duty solenoid connector. Engine must be at normal operating temperature. Disconnect line from wastegate valve controller. Using a "T" fitting, connect an air pressure gauge. Use enough line so that gauge may be carried inside passenger compartment.
2. Boost pressure should be checked at 2400 RPM with a wide open throttle. Normal pressure is 7.2-8.3 psi (2.4-2.8 kg/cm 2 ). Reconnect wastegate duty solenoid.
3. If boost pressure is too high, check the rubber hose that connects the intake manifold to the wastegate valve. Replace if defective. If wastegate valve is not operating and remains closed, replace the turbocharger. If boost pressure is too low, replace the turbocharger.

WASTEGATE DUTY SOLENOID

Disconnect wastegate duty solenoid connector. Using an ohmmeter, measure solenoid resistance. If resistance is not 17-21 ohms, replace solenoid. Check solenoid terminals for a short to ground. Also see appropriate TESTS W/CODES articles.

END PLAY & SIDE PLAY

The maximum end play on the turbine shaft is .0035" (.09 mm). Maximum side play is .0067" (.17 mm). Side play is checked by moving intake and exhaust side of shaft at the same time.

A/C SWITCH

See appropriate L - WIRING DIAGRAM, test switch and circuits as necessary.

AIRFLOW METER

Remove rubber cover from electrical connector on airflow meter. Leave connector connected. Connect volt/ohmmeter between terminals and record readings. See AIRFLOW METER RESISTANCE table. If readings are not to specifications, check electrical wiring. If wiring is okay, replace airflow sensor.

Note. DO NOT start engine during this test. Place the ignition switch in the "OFF" or "ON" position as indicated.

AIRFLOW METER RESISTANCE

Justy

See appropriate HIGH ALTITUDE COMPENSATOR in this article.

See appropriate L - WIRING DIAGRAM article in this section and test switch and/or circuits as necessary.

CLUTCH SWITCH

See appropriate L - WIRING DIAGRAM article in this section and test switch and/or circuits as necessary.

COOLANT TEMPERATURE SENSOR

Disconnect coolant temperature sensor connector. Using an ohmmeter, measure resistance between sensor terminals. See COOLANT TEMPERATURE SENSOR RESISTANCE table.

COOLANT TEMPERATURE SENSOR RESISTANCE

CRANK ANGLE SENSOR

For testing information, see BASIC TESTING .

EGR POSITION SENSOR

See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS and SUB-SYSTEMS in this article.

EGR TEMPERATURE SENSOR (CALIF.)

See TESTS W/CODES and appropriate WIRING DIAGRAMS .

ELECTRICAL LOAD SENSORS

See appropriate L - WIRING DIAGRAM and test switch and/or circuits as necessary.

ENGINE SPEED SENSOR (SPFI)

See FUEL CONTROL in this article.

See appropriate L - WIRING DIAGRAM article in this section and test switch and/or circuits as necessary.

OXYGEN SENSOR

For testing procedures, see appropriate trouble code(s) for rich or lean running in TESTS W/CODES and appropriate WIRING DIAGRAMS .

P/N SWITCH

See TESTS W/CODES article, appropriate L - WIRING DIAGRAM and test switch and circuits as necessary.

Except Justy

For testing, see TESTS W/CODES and appropriate WIRING DIAGRAMS .

See appropriate L - WIRING DIAGRAM article in this section and test switch and related circuits as necessary.

Disconnect 2-wire harness on thermosensor. Measure resistance between each terminal and ground. If sensor does not meet specifications, replace sensor. See JUSTY THERMOSENSOR RESISTANCE table.

JUSTY THERMOSENSOR RESISTANCE

THROTTLE POSITION SENSOR/SWITCH

For testing and adjustments, see ADJUSTMENTS article in this section.

PRESSURE SENSOR

For testing, see TESTS W/CODES and WIRING DIAGRAMS articles in this section.

VEHICLE SPEED SENSOR

For testing, see TESTS W/CODES and WIRING DIAGRAMS articles in this section.

EGR SOLENOID

See EGR SYSTEM under EMISSION SYSTEMS and SUB-SYSTEMS in this article and TESTS W/CODES for appropriate trouble code.

FLOAT BOWL CONTROL SOLENOID

See FUEL EVAPORATION under EMISSION SYSTEMS and SUB-SYSTEMS in this article.

FUEL PUMP RELAY

For testing procedures, see BASIC TESTING and appropriate L - WIRING DIAGRAM.

HIGH ALTITUDE COMPENSATOR SOLENOIDS

See HAC SYSTEM under EMISSION SYSTEMS and SUB-SYSTEMS in this article and TESTS W/CODES for appropriate trouble code.

MAIN RELAY

For testing procedures see BASIC TESTING and appropriate L - WIRING DIAGRAM articles in this section.

PURGE CONTROL SOLENOID

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in this article.

SLOW-CUT SOLENOID VALVE

For testing procedures, see appropriate trouble code in TESTS W/CODES article in this section.

VACUUM LINE CONTROL (VLC) SOLENOID

See HAC SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in this article and TESTS W/CODES for appropriate trouble code(s).

See EGR SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in this article and TESTS W/CODES for appropriate trouble code.

FUEL INJECTOR(S)

1. Connect tachometer to engine. Start engine and run at idle. Remove harness connector from injectors one at a time. Engine idle speed should drop 100-300 RPM as each injector is disconnected. If engine idle speed does not drop, check the wiring connector, injector resistance or injection signal from the computer.
2. Disconnect electrical connector from each injector. Measure injector resistance. See «INJECTOR RESISTANCE SPECIFICATIONS»(/subaru/xt/i-1987-1992/remont/testing-diagnostics/#systemcomponent-tests) table. If injector is not to specification, replace injector.

INJECTOR RESISTANCE SPECIFICATIONS

FUEL INJECTOR RESISTORS (MPFI 1.8L)

Disconnect resistor block. Measure resistance between terminal "W" and to any other terminal. If reading is not 5.8-6.5 ohms, replace resistor block.

KICKDOWN RELAY CONTROL

For testing procedures, see TESTS W/CODES .

SPFI models with automatic seat belts also use an engine speed sensor to operate fuel pump relay. This sensor will also ground the fuel pump control relay, if for some reason the ECU does not. For testing procedures on all models, see BASIC TESTING and appropriate L - WIRING DIAGRAM articles in this section.

For testing procedures see BASIC TESTING and appropriate L - WIRING DIAGRAM articles in this section.

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in this article and TESTS W/CODES article in this section for appropriate trouble code.

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING

Disconnect harness and measure resistance between solenoid terminals. Ensure resistance is 10-100 ohms. If not, replace solenoid(s). Also see appropriate trouble code(s) in TESTS W/CODES article in this section.

FEEDBACK SYSTEM

Manufacturer recommends complete inspection of self-diagnostic system be performed. This would also include checking mechanical condition of engine, available fuel to carburetor or injectors and ignition. Repair or replace components as required and test drive vehicle.

SYSTEM INSPECTION

No inspection procedures are available from the manufacturer. Ensure self-diagnostic system is checked for any trouble codes. Repair components as required. If necessary, check and replace appropriate components.

AUXILIARY AIR VALVE (MPFI 1.8L)

1. With engine running, pinch hose between Auxiliary Air Valve (AAV) and intake manifold. Engine speed should drop (about 100 RPM with engine warm, more with engine cold). Release hose. Ensure engine speed returns to previous speed.
2. If not as specified, turn ignition off. Ensure resistance of AAV is between Zero and Infinity ohms. If not, replace AAV. Check AAV solenoid for any short to ground. If present, replace ACV.
3. Check for voltage at harness connector. Ensure 12 volts are available at Blue wire of AAV electrical connector. If not, check main relay, fuses and power source.

BY-PASS AIR CONTROL VALVE (MPFI 2.7L)

1. Disconnect By-Pass Air Control Valve (BACV) harness connector. Using an ohmmeter, measure resistance between terminals No. 1 and 2 (Yellow/Red and Black/White wires). Resistance should be 9.5-11.5 ohms.
2. Measure resistance between terminals no. 2 and 3 (Black/White and Yellow/Blue wires). Resistance should be 8.5-10.5 ohms. Ensure terminals are not shorted to ground. If BACV does not test as described, replace BACV.

BY-PASS AIR CONTROL VALVE (SPFI)

1. With engine running, disconnect electrical connector. Engine speed should drop (a little with engine warm, a lot with engine cold). Reconnect electrical connector. Ensure engine speed returns to previous speed.
2. If not, turn engine off. Turn ignition switch to "ON" position. Ensure 10-12 volts are available at Black/White wire of air control valve electrical connector.
3. Turn ignition off. Ensure resistance of Air Control Valve (ACV) is 7.3-13 ohms. If not, replace ACV. Check ACV solenoid for any short to ground. If present, replace ACV.
4. Attach electrical connector to ACV. Disconnect connector at ECU. Turn ignition on. Ensure 10-12 volts are present at Green/Red wire (terminal No. 45) of ECU. If not, check harness between ACV and ECU.
5. Turn ignition off and reattach ECU connector. Turn ignition on. Backprobe Green/Red wire (terminal No. 45) of ECU. There should be 1 volt or less for about 1 minute after ignition is turned to "ON" position. After 1 minute, there should be at least 10 volts. If not, check for a bad ground, problem with ECU circuits (sensors) or ECU.

Justy & MPFI

1. Warm engine to operating temperature. With transmission in Neutral, open throttle until dashpot is fully extended.
2. Allow throttle to slowly close. Ensure dashpot end contacts throttle lever between 2200-2400 RPM on Justy or 2800-3400 RPM on MPFI engines. If not, loosen locknut and adjust dashpot.

1. Turn A/C switch on, if equipped. On models without A/C, turn headlight, heater blower, rear defogger and radiator fan on. Ensure Fast Idle Control Device (FICD) solenoid operates.
2. On auto. trans. models, ensure vacuum is applied to mixture by-pass actuator. (Scheme 77) On all models, ensure vacuum is applied to idle-up actuator. If necessary, check and adjust actuator so it opens.030" (.76 mm) man. trans. or.034" (.86 mm) on auto. trans. models. (Scheme 78)

Scheme 77

Scheme 78

FAST IDLE CONTROL DEVICE (MPFI & SPFI)

See appropriate L - WIRING DIAGRAM and test switch and/or circuits as necessary.

Remove top of air cleaner. With engine running, apply a source of heated air to warm up idle compensator. Ensure idle compensator opens and idle speeds up. Allow idle compensator to cool (should close). If idle compensator does not test as described, replace.

Disconnect harness and measure resistance between solenoid terminals. Ensure resistance is 33-40 ohms. (Scheme 79) If not, replace solenoid. Also see appropriate trouble code(s) in TESTS W/CODES.

Scheme 79

IGNITION SYSTEM

Note. For basic ignition checks (coil, wires, crank angle sensor), see BASIC TESTING .

Electronic Advance

For testing, see TESTS W/CODES and WIRING DIAGRAMS articles in this section.

Knock Sensor

For testing, see TESTS W/CODES and WIRING DIAGRAMS articles in this section.

Scheme 80

Suction Valve

1. Blow air through suction valve air inlet section. Air should flow smoothly through to valve outlet. (Scheme 81) If not, reed valve is stuck closed. Replace reed valve.
2. Blow air through valve outlet. If air flows out inlet, reed valve is broken or stuck open. Replace reed valve.
3. Open suction valve. Inspect gasket, inlet case and outlet case for damage (cracks). Clean reed valve with gasoline and inspect for waves, cracks or dents in reed valve seat. Inspect for broken or cracked point of reed valve, or rusted stopper. Replace as required. (Scheme 82)

Scheme 81

Scheme 82

Scheme 83

Scheme 84

EGR System

1. Apply about 8 in. Hg to EGR valve with hand vacuum pump. With engine warmed up, either rough idling or engine stall should occur.
2. If engine idle does not change, check EGR pipe and gas passages for clogging and leaks. Clean or replace if necessary. When cleaning, inspect exhaust gas inlet to intake manifold for presence of deposits. Inspect EGR inlet pipe for exhaust deposits.

EGR Valve

1. Look through opening in EGR valve body. Warm engine to normal operating temperature. Increase engine speed and observe that valve shaft moves when engine reaches 3000-3500 RPM under no-load condition.
2. If shaft does not move, remove valve and manually check valve movement. If valve appears okay, check vacuum lines for leaks. If valve does not operate, clean or replace. NOTE: When cleaning EGR valve, DO NOT wash in solvent or degreaser, or permanent damage to the valve diaphragm will result.
3. Depress valve diaphragm and inspect valve seat area. Inspect valve inlet and outlet for deposits and clean as necessary. Blow clean with compressed air. Recheck valve operation by applying 8 in. Hg with a hand vacuum pump. Install unit using a new gasket.

EGR Solenoid Valve

1. Remove connector from solenoid valve. Measure resistance of solenoid valve. Resistance should be 33-40 ohms. If not, replace solenoid valve.
2. Measure resistance between solenoid valve terminal leads and body ground. If solenoid is shorted, replace solenoid valve.
3. Check vacuum passage for opening and closing operation. On SPFI and Justy engines, when EGR solenoid is not energized, passage between "A" and "B" should be closed and passage between "B" and "C" should be open. (Scheme 85) When solenoid is energized, passage between "A" and "B" should be open and passage between "B" and "C" should be closed.
4. On Federal turbo and MPFI engines, when solenoid is not energized, passage between "A" and "B" should be closed. When solenoid is energized, passage between "A" and "B" should be open. If solenoid valve does not operate properly, replace with a new one.

Scheme 85

Check Valve

Ensure air does not flow from EGR solenoid valve side, to air intake boot side. Ensure air flows from air intake side to EGR solenoid valve side.

Scheme 86

Scheme 87

Scheme 88

System Test

Remove fuel filler cap. Disconnect vent hose between charcoal canister and fuel tank. Blow air toward canister. Check that air flows freely into canister. Blow air toward fuel tank. Check that air flows into tank with a slight resistance from 2-way valve.

Charcoal Canister

1. Remove vacuum hose from canister purge vent port (main purge vent on turbo). (Scheme 89) Blow air into canister purge vent port. Airflow will be blocked if valve is operating properly.
2. Remove hoses from canister's fuel tank and carburetor ports. Blow air into each port. Check that air flows into canister.
3. On Turbo models, remove secondary purge hose. Blow into hose. Air should flow with a slight resistance.

Scheme 89

2-Way Valve

Remove valve from hoses. Mark hoses for reinstallation. Blow air into each valve port. Check that air flows through valve with light resistance. Visually inspect valve for cracks.

Bowl Vent or Purge Control Solenoid Valve

1. Using an ohmmeter, check resistance between terminals of solenoid. If resistance is not 33-40 ohms (16-20 ohms for Justy), replace solenoid valve.
2. Using an ohmmeter, ensure windings are not grounded. Apply battery voltage to valve terminals. Ensure passage opens and closes as voltage is applied and removed.
3. When EGR solenoid is not energized, passage between "A" and "B" should be closed and passage between "B" and "C" should be open. (Scheme 90) When solenoid is energized, passage between "A" and "B" should be open and passage between "B" and "C" should be closed. If solenoid valve does not operate properly, replace with a new one.

Scheme 90

Atmospheric Pressure Sensor

Disconnect vacuum hose for pressure sensor. Turn ignition on. Check for 2-4.5 volts at ECU terminal No. F62-5 (Red/Yellow wire). If voltage is less, check 5-volt reference and ground circuit. If voltage is more, check ground circuit. If circuits okay, replace pressure sensor.

Scheme 91

1. Using an ohmmeter, check resistance between terminals of solenoid. If resistance is not 33-40 ohms, replace solenoid valve.
2. Using an ohmmeter, ensure windings are not grounded. Apply battery voltage to valve terminals. Ensure passage opens and closes as voltage is applied and removed.
3. When solenoid is not energized, passage between "A" and "B" should be closed. (Scheme 91) When solenoid is energized, passage between "A" and "B" should be open. If solenoid valve does not operate properly, replace solenoid valve.

Scheme 92

1. Using an ohmmeter, check resistance between terminals of solenoid. If resistance is not 33-40 ohms, replace solenoid valve.
2. Using an ohmmeter, ensure windings are not grounded. Apply battery voltage to valve terminals. Ensure passage opens and closes as voltage is applied and removed.
3. When solenoid is not energized, passage between "A" and "B" should be closed and open between "B" and "C". (Scheme 92) When solenoid is energized, passage between "A" and "B" should be open and closed between "B" and "C". If solenoid valve does not operate properly, replace solenoid valve.

Scheme 93

Air Control Diaphragm & Valve

1. In warm weather, it may be difficult to find a malfunction in hot air control system. In cold weather, vacuum leaks or faulty air control valve will result in engine stalling or hesitation, increased fuel consumption and/or lack of power.
2. Check vacuum hoses for cracks and proper connections. Inspect air control diaphragm (vacuum motor) with engine stopped.
3. Disconnect vacuum hose from air control diaphragm. Apply vacuum to diaphragm. Valve should rise to open position (hot air inlet uncovered, fresh air inlet blocked).
4. If diaphragm does not hold vacuum, replace it. With valve in open position, pinch hose to trap vacuum. Valve should remain open for at least 30 seconds. If valve closes too soon, replace air control diaphragm.

Note. Engine must be cold before performing this test. Check hoses, air control diaphragm and valve first.

Temperature Sensor Valve

1. Start engine, allow to idle. Observe position of air control valve. Valve should be open (hot air inlet uncovered, fresh air inlet blocked).
2. Continue to observe valve as engine warms up. Air control valve should gradually move to closed position (hot air inlet blocked). If not, replace temperature sensor valve assembly.

Scheme 94

See also:
• AIRFLOW METER RESISTANCE