Compression
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system. |
Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer. See engine analyzer manual for specific instructions.
Check engine compression with engine at normal operating temperature, all spark plugs removed and throttle wide open. See COMPRESSION SPECIFICATIONS table.
| Application | Specification | |
|---|---|---|
| Compression Pressure (1) | ||
| 2.2L & 2.5L (2) | 156-185 psi (11.0-13.0 kg/cm 2 ) | |
| 3.0L (3) | 185-213 psi (13.0-15.0 kg/cm 2 ) | |
| (1) Maximum variation between cylinders is 7 psi (.5 kg/cm 2 ). (2) Engine cranking at 200-300 RPM with throttle open fully. (3) Engine cranking at 350 RPM with throttle open fully. | ||
| (1) | Maximum variation between cylinders is 7 psi (.5 kg/cm 2 ). |
| (2) | Engine cranking at 200-300 RPM with throttle open fully. |
| (3) | Engine cranking at 350 RPM with throttle open fully. |
COMPRESSION SPECIFICATIONS
Intake Manifold Vacuum - Forester, Legacy & Outback 2.5L
Note. Intake manifold vacuum information not available from manufacturer for Impreza, Outback Sport or Outback 3.0L.
- The manifold vacuum can be checked with a vacuum gauge. Disconnect brake vacuum hose at intake manifold. Install vacuum gauge to manifold.
- Keep engine running at idle speed. Read vacuum gauge. Vacuum at idle, with A/C off, should be 17.72 in./Hg (450 mm/Hg). If reading is steady, but lower than normal and becomes more evident as engine temperature increases, check for leaking manifold gasket or damaged vacuum hose.
- If engine speed slowly drops or vacuum gauge reading slowly drops after stabilizing, exhaust backpressure is too high or exhaust system is clogged. If vacuum gauge reading drops lower than normal after stabilizing, check for leaks around cylinders. If vacuum gauge reading suddenly and intermittently drops after stabilizing, check for sticking valves.
- If engine speed gradually increases or vacuum gauge begins to vibrate rapidly at certain speeds and increases as engine speed increases, check for defective ignition system or improper idle adjustment.
FUEL SYSTEMS
Basic diagnosis of fuel system should begin by checking fuel pump operation and fuel system pressure.
| WARNING | Always release fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
FUEL SYSTEM PRESSURE RELEASE
Disconnect fuel pump relay connector. Relay is located at left kick panel. Crank engine for at least 5 seconds. If engine starts, let it run until it stops. Reconnect fuel pump relay connector.
FUEL PRESSURE
Note. Fuel pressure information for Impreza, Outback Sport and Outback 3.0L is not available from manufacturer.
Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Remove fuel filler cap. Disconnect fuel hose at fuel filter and install fuel pressure gauge. Start engine and check fuel pressure at idle. See FUEL PRESSURE AT IDLE table. Verify fuel pressure increases as specified.
| Application | Vacuum Line Connected - psi (kg/cm 2 ) | Vacuum Line Disconnected - psi (kg/cm 2 ) |
|---|---|---|
| Forester, Legacy & Outback 2.5L | 30-34 (2.1-2.4) | 41-46 (2.9-3.2) |
FUEL PRESSURE AT IDLE
FUEL PUMP CONTROL CIRCUIT
Note. For information on testing relays and fuel system components, see SYSTEM & COMPONENT TESTING article. For complete wiring circuit of electrical components on a specific model, see WIRING DIAGRAMS article.
Fuel Pump Relay
Fuel pump relay, located at left kick panel, controls fuel pump operation. When main relay is energized, battery voltage is supplied to one side of fuel pump relay. When ignition is turned on, voltage is supplied from ignition switch to other side of fuel pump relay. When proper input signals are received by Electronic Control Module (ECM), fuel pump relay ground circuit is grounded by ECM. Fuel pump relay then provides voltage to fuel pump for fuel pump operation.
Main Relay
On 3.0L, fuse No. 13 (15-amp) in fuse and relay box, located in left front kick panel, supplies constant battery voltage to one side of main relay. For all other models, slow blow fuse No. 5 in main fuse box, located in front of driver shock tower in engine compartment, supplies constant battery voltage to one side of main relay. On all models, when main relay is energized by ECM, main relay provides voltage to fuel pump relay, oxygen sensors, data link connector (DLC) terminal No. 1, Electronic Control Module (ECM), and various other electrical components.
3.0L
- Remove coil from spark plug. Leave original spark plug installed in cylinder head. Install new spark plug to coil. Ground spark plug against cylinder block. Crank engine with throttle valve fully open and check for spark.
- If spark exists, check fuel pump operation. See «FUEL PUMP OPERATION»(ref-11741-S08545478212000121100000) under FUEL SYSTEMS. If spark does not exist, check ignition system. See IGNITION SYSTEM in SYSTEM & COMPONENT TESTING article.
- If ignition system wiring and control system are okay and spark still does not exist, check resistance of camshaft position sensor. See «CAMSHAFT POSITION SENSOR RESISTANCE»(ref-11741-S01277746862000121500000) . If camshaft position sensor resistance is within specification, go to next step. If camshaft position sensor resistance is not within specification, replace camshaft position sensor and retest for spark. See IGNITION SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article.
- Check resistance of crankshaft position sensor. See «CRANKSHAFT POSITION SENSOR RESISTANCE»(ref-11741-S34979961662000121500000) . If crankshaft position sensor resistance is not within specification, replace crankshaft position sensor and retest for spark. See IGNITION SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article.
2.2L & 2.5L
- Camshaft position sensor is located on camshaft support on left cylinder bank. Disconnect negative battery cable. Disconnect electrical harness connector from camshaft position sensor. Remove bolt attaching camshaft sensor to camshaft support. Remove bolt attaching support to cylinder bank. Remove sensor and support as a unit. Separate sensor from support.
- Using an ohmmeter, check resistance between electrical terminals on camshaft position sensor. Camshaft position sensor resistance should be 1000-4000 ohms. If resistance is not as specified, replace camshaft position sensor.
Scheme 6
- Camshaft position sensor is located on right rear of cylinder head on 3.0L. Disconnect negative battery cable. Remove air cleaner. Disconnect ground cable from fuel pipe protector on right side of engine. Remove fuel pipe protector from right side of engine.
- Disconnect electrical harness connector from camshaft position sensor. Remove bolt attaching camshaft sensor to cylinder head and remove sensor. Using an oscilloscope, check waveform pattern of camshaft position sensor. Camshaft position sensor waveform should closely match that (Scheme 6) If waveform pattern is not as specified, replace camshaft position sensor.
- Crankshaft position sensor is located on oil pump, at front center of cylinder block. Disconnect negative battery cable. Remove bolt attaching crankshaft position sensor to cylinder block. Remove crankshaft position sensor and disconnect electrical harness connector.
- Using an ohmmeter, check resistance between electrical terminals on crankshaft position sensor. Crankshaft position sensor resistance should be 1000-4000 ohms. If resistance is not as specified, replace crankshaft position sensor.
- Crankshaft position sensor is located on top rear of engine, in front of throttle body. Disconnect negative battery cable. Remove air cleaner. Remove engine wiring harness bracket from intake manifold. Remove crankshaft position sensor service hole cover.
- Remove bolt attaching crankshaft position sensor to cylinder block. Remove crankshaft position sensor and disconnect electrical harness connector. Using an ohmmeter, check resistance between electrical terminals on crankshaft position sensor. Crankshaft position sensor resistance should be 800-1300 ohms. If resistance is not as specified, replace crankshaft position sensor.
IGNITION COIL RESISTANCE
Note. Coil-on-plug technology is used on 3.0L. No testing information is available from manufacturer for testing ignition coil resistance.
- Disconnect 4-pin connector from ignition coil and ignitor assembly. Using an ohmmeter, check primary resistance between terminals No. 1 and No. 2 for one coil. Check primary resistance between terminals No. 2 and No. 4 for remaining coil. Resistance should be as specified. (Scheme 7)and «IGNITION COIL RESISTANCE - OHMS @ 68°F (20°C)»(ref-11741-S03050087852000112700000) table. If resistance is not as specified for each coil, replace ignition coil assembly.
- To test secondary resistance, connect ohmmeter between ignition coil secondary terminals No. 1 and No. 2, and terminals No. 3 and No. 4. (Scheme 8) If resistance of each coil is not as specified, replace ignition coil assembly. See «IGNITION COIL RESISTANCE - OHMS @ 68°F (20°C)»(ref-11741-S03050087852000112700000) table.
Scheme 7
Scheme 8
| Application | (1) Primary | (2) Secondary |
|---|---|---|
| 2.2L & 2.5L | .66-.80 | 10,880-14,720 |
| (1) Checked between ignition coil and ignitor assembly connector terminals No. 1 and No. 2 and terminals No. 2 and No. 4. (Scheme 7) (2) Checked between ignition coil secondary terminals for cylinders No. 1 and No. 2, and cylinders No. 3 and No. 4. (Scheme 8) | ||
| (1) | Checked between ignition coil and ignitor assembly connector terminals No. 1 and No. 2 and terminals No. 2 and No. 4. (Scheme 7) |
| (2) | Checked between ignition coil secondary terminals for cylinders No. 1 and No. 2, and cylinders No. 3 and No. 4. (Scheme 8) |
IGNITION COIL RESISTANCE - OHMS @ 68°F (20°C)
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ON-VEHICLE ADJUSTMENTS article.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to SELF-DIAGNOSTICS article. If no hard codes are found in self-diagnostics, go to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.