Engine Controls - Basic Testing Nissan Sentra B13

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/ misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. See M - VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

Compression

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

ENGINE COMPRESSION (4-CYLINDER)

ENGINE COMPRESSION (V6)

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove O2 sensor or air injection check valve (if equipped). Connect a 0-5 psi pressure gauge. Run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi (.12 - .14 kg/cm 2 ), exhaust system or catalytic converter is plugged.

If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port. Start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for a restriction.

FUEL PRESSURE

Basic diagnosis of fuel system should begin with determining fuel system pressure. If fuel pump is inoperative, check fuel pump fuse. If fuse is okay, see FUEL SYSTEM in I - SYS/COMP TESTS article. See L - WIRING DIAGRAMS article for specific circuit or wire color reference.

1. To relieve fuel system pressure, remove fuel pump fuse (fuel pump relay on 300ZX). Start engine and allow to run until engine stalls. Crank engine an additional 2 or 3 times to verify all pressure has dissipated. Turn ignition off. Install fuel pump fuse or relay.
2. Connect fuel gauge between fuel filter outlet and fuel tube using a "T" connector. To prevent inaccurate fuel pressure readings, disconnect electrical connector at fuel pressure regulator control solenoid valve (if equipped). Start engine. Check fuel line connections for leaks.
3. Check fuel pressure with engine idling. Disconnect vacuum hose from pressure regulator and recheck fuel pressure. Compare fuel pressure readings on pressure gauge with specifications in FUEL PRESSURE table.
4. Release fuel system pressure as described in step 1). Disconnect fuel pressure gauge. Reconnect fuel lines. Start engine and check for fuel leaks. If necessary, clear trouble Code 22 from ECU memory.

FUEL PRESSURE - psi (kg/cm 2 )

IGNITION CHECKS

Note. Maxima with VE30DE engine and 300ZX are equipped with Direct Ignition System (DIS).

DISTRIBUTOR TYPE

To determine cause of no spark condition, perform the following tests in the order given. Deviation from this procedure may cause false diagnosis and replacement of non-defective components.

Spark

Check for spark at coil wire and at each spark plug wire using a spark tester. DO NOT crank engine continuously for more than 2 seconds. Inspect secondary coil wire for arcing while testing spark at plugs. Check electrical connections at crank angle sensor, ignition coil and power transistor.

Ignition Coil Power Source

1. Disconnect ignition coil 2-wire connector. Turn ignition on. Check for voltage at wire terminal specified in IGNITION COIL POWER SOURCE TERMINAL IDENTIFICATION table.
2. If voltage is present, go to POWER TRANSISTOR test. If voltage is not present, check continuity of entire circuit between battery and ignition coil, including fuse link and ignition switch.

IGNITION COIL POWER SOURCE TERMINAL IDENTIFICATION

Power Transistor

For power transistor system testing, see appropriate CODE 21 (NO IGNITION REFERENCE) test in TESTS W/CODES article. For power transistor component testing, see IGNITION SYSTEMS in I - SYS/COMP TESTS article.

Ignition Coil Resistance

1. When ignition coil is suspected of causing ignition problems, carefully inspect coil for burned spots indicating secondary circuit arcing to primary or ground circuits. Disconnect ignition coil primary 2-wire connector.
2. Using ohmmeter, check primary resistance between primary connector terminals. Check secondary resistance between secondary tower and positive terminal of coil primary connector. Positive terminal is identified by wire color in IGNITION COIL POWER SOURCE TERMINAL IDENTIFICATION table. If primary or secondary resistance is not as specified in appropriate IGNITION COIL RESISTANCE table, replace ignition coil.

IGNITION COIL RESISTANCE (4-CYLINDER) - Ohms @ 68°F (20°C)

IGNITION COIL RESISTANCE (V6) - Ohms @ 68°F (20°C)

Crank Angle Sensor

1. Crank angle sensor is part of distributor. If a fault is present in crank angle sensor, Code 11 may be set in ECU memory. If Code 11 is set, perform appropriate CODE 11 (CRANK ANGLE SENSOR) test in TESTS W/CODES article.
2. To test crank angle sensor, leave sensor wiring connected. Using a logic probe or DVOM with an analog bar graph function, connect negative lead to ground and alternately connect positive lead to 1-degree (position) signal and 120/180-degree (reference) signal terminals of ECU connector. See CRANK ANGLE SENSOR ECU INPUT SIGNAL TERMINALS table.
3. Measure voltages at both terminals with engine cranking. See CRANK ANGLE SENSOR ECU INPUT SIGNAL VOLTAGES table. If either signal is not present, check harness for short or open circuit. If no problems are found, replace crank angle sensor.

Note. It is possible to measure crank angle sensor voltage with a conventional DVOM without bar graph function; however, it may not be easy to determine peak voltage signal due to averaging of signal.

CRANK ANGLE SENSOR ECU INPUT SIGNAL TERMINALS (1)

CRANK ANGLE SENSOR ECU INPUT SIGNAL VOLTAGES

DIRECT IGNITION SYSTEM (DIS)

To determine cause of no spark condition, perform the following tests in the order given. Deviation from this procedure may cause false diagnosis and replacement of non-defective components.

Ignition Coil Power Source & Ground

1. Disconnect 3-wire ignition coil connector. Turn ignition on. Check voltage between ground and terminal "B" of ignition coil connector. (Scheme 1)
2. If battery voltage is not present, go to IGNITION COIL/POWER TRANSISTOR RELAY test. If battery voltage is present, turn ignition off. Check continuity between ground and terminal "A" of ignition coil connector.
3. If there is no continuity, repair ground circuit between ignition coil connector terminal "A" and ground. Repeat test for each remaining coil.

Scheme 1

Ignition Coil/Power Transistor Relay

Connect a 12-volt power source between relay connector terminals No. 1 and 2. (Scheme 2) Check continuity between terminals No. 3 and 5. If there is no continuity, replace relay. Disconnect power source. Check continuity between relay connector terminals No. 3 and 5. If there is continuity, replace relay.

Scheme 2

Disconnect 3-wire connector from ignition coil. Check primary resistance between terminals "1" and "2" of ignition coil. (Scheme 3) Resistance should be 0.7 ohm.

Scheme 3

1. If a fault is present in crank angle sensor, Code 11 may be set in ECU memory. If Code 11 is set, perform appropriate CODE 11 (CRANK ANGLE SENSOR) test in TESTS W/CODES article.
2. To test crank angle sensor, leave sensor wiring connected. Using a logic probe or DVOM with an analog bar graph function, connect negative lead to ground and alternately connect positive lead to terminals No. 42 and 52 of ECU connector (1-degree input signal). Crank engine and note voltage pulse signals. For ECU connector terminal identification, see «L - WIRING DIAGRAMS»(/nissan/sentra/b13-1990-1994/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article.
3. Alternately probe ECU connector terminals No. 41 and 51 (120-degree input signals). Crank engine and note voltage pulse signals.
4. Peak voltage for 1-degree signal should measure about 2.5-2.7 volts on bar graph DVOM. Peak voltage for 120-degree signal should measure about 1.2-1.4 volts. If 1-degree or 120-degree signal is not present, check harness for short or open circuit. If no problems are found, replace crank angle sensor.

Note. It is possible to measure crank angle sensor voltage with a conventional DVOM (no bar graph function); however, it may not be easy to determine peak voltage signal due to averaging of digital signal.

Power Transistor Circuits

1. Disconnect 7-pin connector from power transistor unit. Disconnect 3-wire ignition coil connector.
2. Check continuity of each circuit between ignition coil connector terminal "C" and corresponding wire terminal of power transistor unit 7-pin connector. (Scheme 1) For wire colors and related ECU connector terminals, see «L - WIRING DIAGRAMS»(/nissan/sentra/b13-1990-1994/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article. Repair as necessary.
3. Disconnect power transistor unit 6-pin connector. Disconnect ECU connector. Check continuity of each wire circuit between power transistor unit and corresponding wire terminal of ECU connector. See «L - WIRING DIAGRAMS»(/nissan/sentra/b13-1990-1994/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article.
4. If continuity does not exist in any of power transistor 6-pin connector wire terminals, repair open circuit in wires. If there is continuity in all wires but one or more ignition coils is inoperative, reconnect all connectors. Go to ECU POWER TRANSISTOR OUTPUT SIGNAL test.

ECU Power Transistor Output Signal

1. Using a logic probe or DVOM with an analog bar graph function, carefully backprobe 20-pin ECU connector terminals No. 1, 2, 3, 11, 12 and 13 while cranking engine. This tests ECU output signals that trigger power transistor unit.
2. If pulse signals of about 0.1 volt are present at each specified ECU terminal, replace power transistor unit. If pulse signals are not available at any terminal, go to next step.
3. While cranking engine, check for battery voltage at terminal No. 43 (start signal) of ECU connector. If battery voltage is not present during cranking, repair start signal circuit and retest.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. Improper setting of ignition timing and idle speed may cause driveability problems and/or false setting of trouble codes. For adjustment procedures, see ADJUSTMENTS article.

4-CYLINDER IDLE SPEED & CO LEVEL

V6 IDLE SPEED & CO LEVEL

4-CYLINDER IGNITION TIMING (Degrees BTDC @ RPM)

V6 IGNITION TIMING (Degrees BTDC @ RPM)

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES article. If no hard codes are found in self-diagnostics or vehicle does not have a self-diagnostic system, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

See also:
• L - WIRING DIAGRAMS