Engine Controls - Basic Testing: Other Subaru Impreza GC/GF

Compression

Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer. See engine analyzer manual for specific instructions.

Exhaust System Backpressure

1. The exhaust system can be checked with a vacuum or pressure gauge. Remove HO2S sensor or air injection check valve (if equipped).
2. Connect a 1-10 psi pressure gauge and operate engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.
3. If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold it steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

FUEL PRESSURE

Basic diagnosis of fuel system should begin by determining fuel system pressure. If fuel pump is inoperative, see appropriate test under FUEL PUMP CIRCUIT TESTS .

Relieving Fuel Pressure

1. Disconnect fuel pump connector. Crank engine for at least 5 seconds. If engine starts, let it run until it stops. Disconnect fuel hose at pressure regulator and install fuel pressure gauge using "T" connector.
2. Start engine and check fuel pressure at idle. See the «REGULATED FUEL PRESSURE»(ref-26157-S34696590662001010500000) table. Verify fuel pressure increases as engine speed increases.

REGULATED FUEL PRESSURE

IGNITION CHECKS

Note. Also see appropriate test under IGNITION CONTROL SYSTEM TESTS.

SPARK

Check for spark at spark plug wires using a spark tester. Check resistance of each spark plug wire. Replace wire if resistance is not within specification. See HIGH TENSION WIRE RESISTANCE table.

HIGH TENSION WIRE RESISTANCE

IGNITION COIL RESISTANCE

1. Disconnect 3-wire connector from ignition coil assembly. Using an ohmmeter, check primary resistance between terminals No. 1 and 2 for one coil. (Scheme 30)
2. Check primary resistance between terminals No. 2 and 3 for remaining coil. Resistance should be as specified. See the «IGNITION COIL RESISTANCE»(ref-26157-S20853188202001010500000) table. If resistance is not as specified for each coil, replace ignition coil assembly.
3. To test secondary resistance, connect one ohmmeter lead to tower at one end of coil. Connect remaining ohmmeter lead to tower at opposite end of same coil.
4. Repeat test for other coils. If resistance of each coil is not as specified, replace ignition coil assembly.

Scheme 30

IGNITION COIL RESISTANCE - OHMS @ 68°F (20°C)

CRANKSHAFT POSITION SENSOR & TDC SENSOR SIGNALS

Note. For crankshaft position and TDC sensor signal testing, see the TESTS W/CODES article.

IDLE SPEED & IGNITION TIMING

Verify idle speed and ignition timing are set to specification. See IDLE SPEED SPECIFICATIONS and IGNITION TIMING tables. For adjustment procedures, see the ADJUSTMENTS article.

IDLE SPEED SPECIFICATIONS

IGNITION TIMING (Degrees BTDC @ RPM)

ECU POWER SUPPLY & GROUND TESTS

1. Check Main Relay - Turn ignition off and remove main relay. Connect battery voltage to main relay terminals No. 1 (Black/Blue Wire) and 2 (Light Green/White wire). Ensure there is less than 10 ohms resistance between main relay terminals No. 3 (Red wire) and 5 (Light Green/Red wire), and between terminals No. 4 (Green/Black wire) and 6 (Green/White wire). If resistance is less than 10 ohms, go to next step. If resistance is more than 10 ohms, replace main relay.
2. Check ECU Power Supply Circuit - Install main relay and disconnect connectors from ECU. Turn ignition on. Ensure there is at least 10 volts between ECU connector terminals No. 15 (Brown wire) and No. 96, No. 16 (Blue/Yellow wire) and No. 96, and No. 42 (Yellow/Green wire) and No. 96. If at least 10 volts are present, go to next step. If at least 10 volts are not present, repair harness or connectors as necessary.
3. Check ECU Ground Circuit - Turn ignition off. Ensure there is less than 5 ohms harness resistance between ECU connector terminals No. 25 (Black/Green wire) and ground, No. 45 (Black/Red wire) and ground, No. 46 (Black/Red wire) and ground, No. 69 (Black wire) and ground, No. 70 (Black/Green wire) and ground, No. 71 (Black/Yellow wire) and ground, No. 72 (Black/Yellow wire) and ground, No. 95 (Black/Green wire) and ground, and No. 96 (Black/Green wire) and ground. If resistance is less than 5 ohms, see «IGNITION CONTROL SYSTEM TESTS»(ref-26157-S27184940732001010500000) . If resistance is more than 5 ohms, repair harness or connectors as necessary.

IGNITION CONTROL SYSTEM TESTS

1. Check Ignition System For Proper Spark - Remove injector sub-harness and plug wire cap from each spark plug. Install a known good spark plug to plug wire and position spark plug so it is grounded to engine. Ensure each spark plug sparks as engine is cranking. If a spark does not occur at each spark plug, connect injector sub-harness and plug wires and go to next step. If a spark does occur at each spark plug, see «FUEL PUMP CIRCUIT TESTS»(ref-26157-S07722669732001010500000).
2. Check Ignition Coil Power Supply Circuit - Turn ignition off and disconnect Gray 3-pin ignition coil connector. Turn ignition on. Ensure there is at least 10 volts between ignition coil connector terminal No. 2 (Blue/Red wire) and ground. If at least 10 volts are present, go to next step. If at least 10 volts are not present, repair harness or connectors as necessary.
3. Check Ignition Coil - Ensure there is.7 ohm resistance between ignition coil connector terminals No. 1 and 2, and No. 2 and 3. Ensure there is 13,800 ohms resistance between spark plug wire towers opposite each other. If specified resistance is present, go to next step. If specified resistance is not present, replace ignition coil. (Scheme 30)
4. Check Harness Connector Between Ignition Coil & Ignitor - Turn ignition off and disconnect Gray 6-pin ignitor connector. Measure harness resistance between ignition coil connector terminal No. 1 (Blue/Red wire) and ignitor connector terminal No. 5 (Blue wire), and between coil connector terminal No. 3 (Red/Green wire) and ignitor connector terminal No. 6 (Red/Green wire). If resistance is less than 10 ohms, go to next step. If resistance is more than 10 ohms, repair or replace harness connector as necessary.
5. Check Input Signal For Ignitor - Turn ignition off and connect ignition coil and ignitor connectors. Measure voltage between ignitor6-pin connector terminal No. 1 (Yellow/Blue wire) and ground, and between terminal No. 2 (Green/White wire) and ground. Crank engine and verify voltage fluctuates between.1-3.4 volts. If voltage fluctuates, go to next step. If voltage does not fluctuate, replace ignitor.
6. Check Ignitor Harness Connector Ground Circuit - Turn ignition off. Ensure there is less than 10 ohms resistance between ignitor connector terminal No. 3 (Black wire) and ground. If resistance is as specified, go to next step. If resistance is not as specified, repair harness or connectors as necessary.
7. Check Harness Connector Between ECU & Ignitor - Turn ignition off. Disconnect ECU 26-pin and 22-pin Green connectors. Ensure there is less than 10 ohms resistance between ECU connectors and ignitor connector. Measure between 22-pin connector terminal No. 20 (Green/White wire) and ignitor connector terminal No. 2 (Green/White wire), and between terminal No. 21 (Yellow/Blue wire) and terminal No. 1 (Yellow/Blue wire).
8. On ECU 26-pin connector, measure between terminal No. 14 (Black wire) and ignitor 6-pin connector terminal No. 3 (Black wire). Ensure there is one megohm resistance between 22-pin connector terminal No. 20 (Green/White wire) and ground, terminal No. 21 (Yellow/Blue wire) and ground, and 26-pin connector terminal No. 14 (Black wire) and ground. If harness resistance is not as specified, repair harness or connectors as necessary. If harness resistance is as specified, inspect and repair ECU connectors. If ECU connectors are okay, replace ECU.

FUEL PUMP CIRCUIT TESTS

1. Check Fuel Pump Operation - Ensure there is fuel pump operation for 2 seconds after turning ignition on. If fuel pump operates for 2 seconds, check fuel injector circuit. See «FUEL INJECTOR CIRCUIT TESTS»(ref-26157-S30621711762001010500000). If fuel pump does not operate, go to next step.
2. Check Fuel Pump Ground Circuit - Turn ignition off and disconnect fuel pump 6-pin connector. Ensure there is less than 10 ohms resistance between connector terminal No. 3 and ground. If resistance is less than 10 ohms, go to next step. If resistance is more than 10 ohms, repair harness or connectors as necessary.
3. Check Fuel Pump Power Supply - Turn ignition on. Ensure there is at least 10 volts between fuel pump 6-pin connector terminal No. 1 (Blue/Yellow wire) and ground. If at least 10 volts are not present, go to next step. If at least 10 volts are present, replace fuel pump.
4. Check Harness Resistance Between Fuel Pump & Fuel Pump Relay - Turn ignition off. Ensure there is less than 10 ohms resistance between fuel pump connector terminal No. 1 (Blue/Yellow wire) and fuel pump relay 4-pin connector terminal No. 4 (Black/Red wire). If resistance is less than 10 ohms, go to next step. If resistance is more than 10 ohms, repair harness or connectors as necessary.
5. Check Fuel Pump Relay - Disconnect fuel pump relay 4-pin connector and main relay 6-pin connector. Remove fuel pump relay and main relay with bracket. Connect battery voltage to fuel pump relay terminals No. 1 and 3. Ensure there is less than 10 ohms resistance between terminals No. 2 and 4. If resistance is less than 10 ohms, go to next step. If resistance is greater than 10 ohms, replace fuel pump relay. (Scheme 31)
6. Check Harness Resistance Between ECU & Fuel Pump Relay - Disconnect ECU connectors. Ensure there is less than 10 ohms resistance between ECU 26-pin connector terminal No. 8 (Light Green/Black wire) and fuel pump relay connector terminal No. 3 (Light Green/Black wire). If more than 10 ohms is present, repair harness or connectors as necessary. If less than 10 ohms is present, inspect ECU connector terminal. If ECU connector is okay, replace ECU.

Scheme 31

FUEL INJECTOR CIRCUIT TESTS

1. Check Fuel Injector Operation - Using a stethoscope, ensure there are injector operating sounds while engine is cranking. If operating sounds are not heard, go to next step. If operating sounds are heard, verify fuel pressure. See «FUEL PRESSURE»(ref-26157-S41925579572001010500000) under FUEL SYSTEM.
2. Check Fuel Injector Power Circuit - Turn ignition off and disconnect each fuel injector connector. Turn ignition on. Measure voltage between each injector connector terminal No. 2 (Yellow wire) and ground. If at least 10 volts are present, go to next step. If less than 9 volts are present, repair harness or connectors as necessary.
3. Check Fuel Injectors - Measure resistance between terminals No. 1 and 2 of each fuel injector. Resistance between terminals should be 11-12 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace fuel injector(s). (Scheme 32)
4. Check Resistance Between ECU Connector & Each Injector - Disconnect ECU 22-pin connector. Ensure there is less than 10 ohms resistance between ECU connector terminals No. 1 (Light Green/Red wire), No. 2 (Brown wire), No. 12 (Blue/Red wire), No. 13 (Blue/White wire) and fuel injector terminal No. 1 of each fuel injector connector. If resistance is greater than 10 ohms, repair harness or connectors as necessary. If resistance is less than 10 ohms, inspect ECU connector and repair as necessary. If ECU connector is okay, replace ECU.

Scheme 32

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to the TESTS W/CODES article. If no hard codes are found in self-diagnostics, go to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.