RETRIEVE & RECORD CODES
Prior to conducting a physical mechanical inspection, retrieve and record any Diagnostic Trouble Codes (DTCs) that are currently set in Engine Control Module (ECM) memory. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. Record any DTCs that are present at this time. Review recovered DTCs, if set, or if battery is disconnected or other DTCs are set during mechanical inspection portion of basic diagnostic procedures.
Compression
Note. Ensure battery is fully charged to obtain specified cranking speed.
Note. If cylinder compression in one or more cylinders is low, repeat inspection using a small amount of oil poured into each cylinder. If compression pressure increases, piston rings may be worn or damaged. If compression pressure does not increase, a valve may be sticking or seating improperly. If compression in any 2 adjacent cylinders is low and does not change after oil is added, cylinder head gasket may be leaking.
Start engine and warm to normal operating temperature. Turn ignition off. Release fuel pressure. See FUEL SYSTEM . On Q45, remove all ignition coils. On G20, disconnect distributor 2-pin harness connector (for ignition coil). On all models, remove all spark plugs. Depress accelerator pedal fully to hold throttle valve wide open. Attach compression tester to cylinder No. 1. Crank engine at specified speed and record highest gauge indication. See COMPRESSION SPECIFICATIONS table. Repeat measurement for each cylinder.
| Application | Psi (kg/cm 2 ) | |
|---|---|---|
| G20 | ||
| Standard | 185 (13.0) | |
| Minimum | 156 (11.0) | |
| Maximum Variation Between Cylinders | 14 (1.0) | |
| Q45 | ||
| Standard | 186 (13.1) | |
| Minimum | 144 (10.1) | |
| Maximum Variation Between Cylinders | 14 (1.0) | |
| (1) With engine at 300 RPM. | ||
| (1) | With engine at 300 RPM. |
COMPRESSION SPECIFICATIONS (1)
Exhaust System Backpressure
Exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove HO2S sensor. Connect a 1-5 psi pressure gauge, and run engine at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.
If a vacuum gauge is used, connect it to intake manifold vacuum. Observe vacuum gauge reading at idle. Open throttle part way (about 2500 RPM) and hold steady. If vacuum gauge slowly drops after stabilizing, exhaust system should be checked for a restriction.
FUEL PRESSURE
Basic diagnosis of fuel system should begin with determining fuel system pressure.
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
Fuel Pressure Release
Remove fuel pump fuse. Start engine and allow to run until engine stalls due to lack of fuel. Crank engine 2-3 more times to verify all pressure has dissipated.
Checking Fuel Pressure
- Release fuel pressure. See «FUEL PRESSURE RELEASE»(ref-3083-S13677854742000041700000) . Disconnect fuel hose on fuel filter outlet side and install fuel pressure gauge. Replace pump fuse. Start engine and check fuel line connections for leakage. Check fuel pressure with engine idling. Record fuel pressure gauge reading.
- Disconnect and plug vacuum hose from pressure regulator and immediately note fuel pressure. Record fuel pressure gauge reading. See «FUEL PRESSURE»(ref-3083-S31026580162000041700000) table.
- Connect a hand-held vacuum pump to fuel pressure regulator. Start engine and watch fuel pressure gauge as vacuum is changed. Fuel pressure should decrease as vacuum increases. If result is not as specified, replace fuel pressure regulator.
| Application | (1) psi (kg/cm 2 ) | (2) psi (kg/cm 2 ) |
|---|---|---|
| G20 & Q45 | 34 (2.4) | 43 (3.0) |
| (1) With vacuum hose connected at fuel pressure regulator. (2) With vacuum hose disconnected at fuel pressure regulator. | ||
| (1) | With vacuum hose connected at fuel pressure regulator. |
| (2) | With vacuum hose disconnected at fuel pressure regulator. |
FUEL PRESSURE
Spark
Check for spark at each spark plug wire using spark tester. Check spark plug wire resistance on suspect wires. Resistance should be 4.15-5.61 k/ohms per foot at 77°F (25°C). Check ignition coil, power transistor and circuits. See DTC P1320: IGNITION SIGNAL under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - G20 article.
Power Transistor
Power transistor is located in distributor. Disconnect distributor 2-pin and 6-pin harness connectors. Measure resistance between distributor 2-pin connector terminal No. 7 (Green wire) distributor 6-pin connector terminal No. 5 (Black wire). If resistance is zero ohms, replace distributor assembly.
Ignition Coil Resistance
Ignition coil is located in distributor. Disconnect distributor 2-pin harness connector. Remove distributor cap. Measure resistance between distributor 2-pin connector terminals. Also measure resistance between ignition coil tower and distributor 2-pin connector terminal No. 8. (Scheme 1) See IGNITION COIL RESISTANCE table.
| Application | Resistance @ 77°F (25°C) |
|---|---|
| Primary (1) | About 0.8 Ohm |
| Secondary (2) | About 16K/Ohms |
| (1) Measured between distributor 2-pin connector terminals. (2) (Scheme 1) | |
| (1) | Measured between distributor 2-pin connector terminals. |
| (2) | (Scheme 1) |
IGNITION COIL RESISTANCE
Scheme 1
Resistor
Resistor is built into distributor cap. Remove distributor cap. Measure resistance between center terminal (rotor) and ignition coil terminal (coil output). (Scheme 2) Resistance should be 4-8 k/ohms at 77°F (25°C).
Scheme 2
Camshaft Position (CMP) Sensor
CMP sensor is located in distributor. For CMP sensor testing, see DTC P0340: CAMSHAFT POSITION (CMP) SENSOR under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - G20 article.
Remove each ignition coil, leaving harness connected. Connect a known good spark plug to ignition coil. Place end of Spark plug against a suitable ground. Crank engine and check for spark. If spark does not exist, check ignition coil, power transistor and circuits. See DTC P1320: IGNITION SIGNAL under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - Q45 article.
Ignition Coil/Power Transistor Resistance
Disconnect ignition coil/power transistor harness connector. Measure resistance between terminals No. 2 and 3. If resistance is zero ohms, replace ignition coil/power transistor.
See DTC P0340: CAMSHAFT POSITION (CMP) SENSOR under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - Q45 article.
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ON-VEHICLE ADJUSTMENTS article.
| Application | (1) Idle RPM |
|---|---|
| G20 | 750-850 |
| Q45 | 600-700 |
| (1) With transmission in Neutral and no electrical load on engine. | |
| (1) | With transmission in Neutral and no electrical load on engine. |
IDLE SPEED
| Application | (1) Specification |
|---|---|
| G20 & Q45 | 13-17° BTDC |
| (1) With transmission in Neutral and no electrical load on engine. | |
| (1) | With transmission in Neutral and no electrical load on engine. |
IGNITION TIMING (Degrees BTDC @ Idle)
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to SELF-DIAGNOSTICS article. If no DTC is found performing self-diagnostics, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.