Engine Controls - Basic Testing: Other Infiniti G20 I

Compression (G20)

Check engine compression at normal operating temperature at specified cranking speed. Release fuel pressure. See FUEL SYSTEM. Disconnect coil wire at distributor. Remove all spark plugs. Depress accelerator pedal fully to hold throttle valve wide open. See COMPRESSION SPECIFICATIONS table.

Compression (J30)

Check engine compression at normal operating temperature at specified cranking speed. Release fuel pressure. See FUEL SYSTEM. Disconnect crankshaft position sensor harness connector. Remove all spark plugs. Depress accelerator pedal fully to hold throttle valve wide open. See COMPRESSION SPECIFICATIONS table.

Compression (Q45)

Check engine compression at normal operating temperature at specified cranking speed. Release fuel pressure. See FUEL SYSTEM. Remove left air duct and disconnect power transistor connectors. Remove left harness connector bracket and ornamental rocker covers. Disconnect harness connector between ignition coil and power transistor. Remove ignition coil bracket and bracket with ignition coils. Remove all spark plugs. Depress accelerator pedal fully to hold throttle valve wide open. See COMPRESSION SPECIFICATIONS table.

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, there is a leak past head gasket. Make repairs as needed and reinspect.

COMPRESSION SPECIFICATIONS (1)

Exhaust System Backpressure

Exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove HO2S sensor. Connect a 1-10 psi (.07-.70 kg/cm 2 ) pressure gauge, and run engine at 2500 RPM. If exhaust system backpressure is greater than 1.75-2.00 psi (.12-.14 kg/cm 2 ), 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.

Relieving Fuel Pressure

To relieve pressure, 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

1. 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.
2. Disconnect and plug vacuum hose from pressure regulator and immediately note fuel pressure. Record fuel pressure gauge reading. See FUEL PRESSURE table.
3. 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.

FUEL PRESSURE

DISTRIBUTORLESS IGNITION SYSTEM CHECKS (J30 & Q45)

To determine cause of a no-spark condition, following steps must be performed in order given. Deviation from this procedure may cause false diagnosis and replacement of non-defective components.

Ignition Coil Power Source

1. Turn ignition off. Disconnect ignition coil relay harness connector. Turn ignition on. Connect negative voltmeter lead to ground. On J30, connect positive lead to one harness Yellow/Black wire and then to the other Yellow/Black wire. On Q45, connect positive lead to harness Black/White wire and then to harness White/Black wire. On all models, battery voltage should be present on both terminals.
2. On J30, if battery voltage is not present, check harness continuity between ECCS relay and EFI harness connector (Yellow/Black wire) and 7.5 amp fuse in fuse box. On Q45, if battery voltage is not present, check main harness connector, 30-amp fusible link in relay block, harness continuity between ignition coil relay and ignition switch, and harness continuity between ignition coil relay and battery. Repair or replace as necessary.

Ground Circuit

1. Turn ignition off. On J30, disconnect ECM harness connector. Check continuity between engine ground and ECM harness connector terminals No. 10, 20, 50, 60, 107, 108 and 116 (Black wire). Continuity should be present. If continuity is not present, repair harness or connector. On Q45, disconnect ignition coil sub-harness connector and ignition coil relay harness connector. Check continuity between ignition coil relay harness connector terminal No. 5 (Brown/Yellow wire) and ignition coil sub-harness connector. Continuity should be present. If continuity is not present, check harness connector to ECM and ignition coil sub-harness connector.
2. On all models, disconnect power transistor unit harness connector. Check continuity between Black wire on harness connectors and ground. Continuity should be present. If continuity is not present, check harness connector between power transistor unit and engine ground.

Output Signal Circuit

1. Turn ignition off. Disconnect ECM and ignition coil relay harness connectors. Check continuity between ECM terminal No. 16 (harness side) and ignition coil relay connector terminal No. 1 (Gray/Red wire). See WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. If continuity is present, go to next step. If continuity is not present, check harness and connectors between ECM and ignition coil relay. Repair as necessary and repeat step 1).
2. Check harness continuity between ECM and ignition coil in each cylinder. (Scheme 1)or (Scheme 2). Continuity should be present. If continuity is not present, repair or replace harness or connectors.

Scheme 1

Scheme 2

Ignition Coil Resistance

On J30, disconnect ignition coil harness connector. Using ohmmeter, check resistance between coil terminals No. 1 and 2. Resistance should be approximately.9 ohm. If resistance is not as specified, replace ignition coil. (Scheme 3)

On Q45, disconnect ignition coil harness connector. Using ohmmeter, check resistance between coil terminals No. 1 and 2 (cylinders No. 1 and 2) and terminals No. 2 and 3 (cylinders No. 3-8). (Scheme 3) Resistance should be approximately.7 ohm. If resistance is not as specified, replace ignition coil.

Scheme 3

Power Transistor

Disconnect power transistor harness connector. Using ohmmeter, check power transistor continuity. (Scheme 4)or (Scheme 5). Replace power transistor if results are not as specified.

Scheme 4

Scheme 5

Power Transistor Relay

1. On J30 and Q45, connect a 12-volt power source and ground to terminals No. 1 and 2 of relay. (Scheme 6) Using ohmmeter, check continuity between terminals No. 3 and 5. Continuity should exist while relay is energized.
2. Disconnect power source and recheck continuity across terminals No. 3 and 5. No continuity should exist. If continuity exists, check harness and connectors. If harness and connectors are okay, replace power transistor relay.

Scheme 6

Crankshaft Position Sensor

1. Remove crankshaft position sensor from engine. DO NOT disconnect crankshaft position sensor harness connector. Turn ignition on (engine off).
2. Connect negative lead of an analog voltmeter to ground. Rotate crankshaft position sensor shaft slowly by hand. Connect positive voltmeter lead to crankshaft position sensor connector terminal No. 1 (one-degree signal, J30; 90-degree signal, Q45). Voltage should fluctuate between zero and 5 volts. Move voltmeter positive lead to terminal No. 2 (120-degree signal, J30; one-degree signal, Q45). Voltage should again fluctuate between zero and 5 volts. (Scheme 7)

Scheme 7

Sub-Crankshaft Position Sensor Signal (Q45)

Set analog voltmeter to 100-mV AC scale. Connect positive voltmeter lead to terminal "a" and negative voltmeter lead to terminal "b" of sub-crankshaft position sensor terminal connector. (Scheme 7) Rotate crankshaft position sensor shaft slowly by hand; voltmeter should deflect. If analog voltmeter does not deflect, replace crankshaft position sensor.

OPTICAL IGNITION SYSTEM CHECKS (G20)

To determine cause of a no-spark condition, following steps must be performed in order given. Deviation from this procedure may cause false diagnosis and replacement of non-defective components.

Spark

Disconnect ignition wire from spark plug. Connect a known good plug to ignition wire and ground spark plug. Crank engine and check for spark at spark plug. Crank engine in short bursts. DO NOT crank engine more than 2 seconds continuously. Repeat for each spark plug.

1. Disconnect ignition coil harness connector. Turn ignition on. Using voltmeter, check voltage between ignition coil harness connector terminal "a" and ground. Battery voltage should be present. 2) If battery voltage is not present, check harness connectors. Check harness continuity between ignition coil and ignition switch. Repair or replace as necessary.

1. Turn ignition off. Disconnect power transistor and ignition coil harness connectors. Check continuity between ignition coil terminal "b" to power transistor terminal "e" (Green/Yellow wire). (Scheme 8)
2. Connect ohmmeter leads between power transistor terminal "d" and ground. (Scheme 8) If continuity does not exist at all these terminals, check and repair wiring harness or connectors.

Scheme 8

Check harness continuity between power transistor terminal "c" and ECM terminal No. 1. Continuity should be present. If continuity is not present, repair or replace wiring harness or connectors.

Input Signal Circuit

Turn ignition off. Disconnect ignition coil, resistor and condenser, and ECM harness connectors. Using ohmmeter, check continuity between ECM terminal No. 3 and resistor and condenser terminal "g" (Yellow/Red wire). Check continuity between ignition coil terminal "b" and resistor and condenser terminal "f" (Green/Yellow wire). Continuity should be present. If continuity is not present, repair or replace wiring harness or connectors.

Disconnect ignition coil harness connector. Using ohmmeter, check resistance between ignition coil terminals No. 1 and 2. Resistance should be about one ohm. Check resistance between ignition coil terminals No. 1 and 3. Resistance should be approximately 10,000 ohms.

Disconnect power transistor harness connector. Using digital ohmmeter, check power transistor continuity. (Scheme 9) Replace power transistor if results are not as specified.

Scheme 9

1. Remove distributor (with internal crankshaft position sensor) from engine. DO NOT disconnect crankshaft position sensor harness connector. Turn ignition on.
2. Connect negative lead of an analog voltmeter to ground. Rotate crank angle sensor shaft slowly by hand. Connect positive voltmeter lead to crankshaft position sensor connector terminal "a" (180-degree signal). (Scheme 10) Voltage should fluctuate between 0 and 5 volts. Move voltmeter positive lead to terminal "d" (one-degree signal). Voltage should again fluctuate between 0 and 5 volts.

Scheme 10

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

IDLE SPEED

IGNITION TIMING (Degrees BTDC @ RPM)

SUMMARY

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