Engine Controls - Basic Testing Honda Accord IV

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. Test drive vehicle under conditions that 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 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, for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. See VACUUM DIAGRAMS article in the ENGINE PERFORMANCE section to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Compression

1. Check engine mechanical condition using a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions.
2. Check compression pressure with engine at normal operating temperature, all spark plugs removed, throttle valves wide open and at specified cranking speed. Crank engine at least 6 revolutions to determine engine compression. Compression reading should be as specified in «ENGINE COMPRESSION»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. CAUTION: 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. ENGINE COMPRESSION (1) Model Standard psi (kg/cm 2 ) Minimum psi (kg/cm 2 ) Minimum RPM Accord 178 (12.5) 135 (9.5) 250 (1) Maximum variation between cylinders is 28 psi (2.0 kg/cm 2 ).

Exhaust System Backpressure

Exhaust system can be checked with a vacuum or pressure gauge. Remove O2 sensor or air injection check valve (if equipped). Connect a 1-10 psi pressure gauge, and 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 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 steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.

FUEL PRESSURE

Relieving Fuel Pressure

Remove negative battery cable. Loosen fuel tank filler cap. Place clean shop rag around fuel filter. Slowly loosen 6-mm bolt on top of fuel filter (one complete turn) to relieve system pressure. Always replace washer under 6-mm bolt after loosening.

Basic Diagnosis

Basic diagnosis of fuel system should begin with determining fuel system pressure. If fuel pump fails to run on fuel-injected models, inspect power supply to main relay. If all power supplies are present (i.e. battery, ignition and starter switch during cranking), perform functional test of main relay. See WIRING DIAGRAMS and SYSTEM/COMPONENT TESTS articles in the ENGINE PERFORMANCE section.

Scheme 1

1. Disconnect negative battery cable. Relieve fuel pressure. See «RELIEVING FUEL PRESSURE»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing__relieving-fuel-pressure). Connect Fuel Pressure Gauge (07406-0040001 ) at 6-mm bolt. Reconnect negative battery cable. Start engine, and note fuel pressure. If vehicle will not start, check for spark. If spark is present and no fuel pressure is evident, inspect fuel pump main relay.
2. Remove connector from fuel pump main relay. (Scheme 1) Using a test light, check for power on Black/Yellow wire at fuel pump relay connector. If power is present, connect a jumper wire between Black/Yellow wire (B+) and Yellow wire. If fuel pump runs, proceed to step 3). If fuel pump fails to run, see «SYSTEM/COMPONENT TESTS»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) article in the ENGINE PERFORMANCE section. If no voltage is present on the Black/Yellow wire, check for open in wire between fuel pump main relay connector and No. 2 fuse on fuse box. Proceed to step 3) after repairing circuit.
3. Start engine. Disconnect vacuum hose from pressure regulator and check for manifold vacuum. If vacuum is not present, check for restriction in vacuum port or hose. Plug vacuum hose and inspect fuel pressure gauge reading. Gauge reading should be within specification. See «FUEL PRESSURE»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. Pressure should drop slightly when vacuum hose is reconnected. FUEL PRESSURE (1) Application At Idle psi (kg/cm 2 ) Accord 34-41 (2.40-2.90) (1) Fuel pressure is tested with vacuum hose removed from pressure regulator.
4. If pressure is higher than specified, inspect for pinched or clogged fuel return line between fuel rail and fuel tank. If no problem is found in fuel line, replace pressure regulator.
5. If pressure is lower than specified, inspect for plugged fuel filter. If filter is not plugged, lightly pinch fuel return line. If fuel pressure does not rise, replace fuel pump. If fuel pressure rises, replace pressure regulator. NOTE: If vehicle starts and runs, fuel pump main relay is okay.

Spark

Check for spark at secondary coil wire and each spark plug wire using a spark tester. If spark is not present, continue with following tests. Check spark plug wire resistance on suspect wires. Resistance should be less than 25,000 ohms.

Ignition Coil Power Source

1. Remove distributor cap to check power source directly at coil. (Scheme 2) On all models, disconnect ignition coil primary leads. Turn ignition on. Using voltmeter, check voltage between ground and Black/Yellow wire terminal of ignition coil harness.
2. Battery voltage should be present. If battery voltage is not present, check for open in Black/Yellow wire between coil and ignition switch. On some models, an in-line radio noise condenser (mounted on distributor or near coil) is utilized. If condenser shorts out, power supply will be interrupted and vehicle will not start.

Ignitor Power Source

Turn ignition off. Disconnect harness connector at distributor. Turn ignition on. Using voltmeter, check for battery voltage between ground and Black/Yellow wire of harness. If voltage is not present, check for open in Black/Yellow wire between ignition coil and harness connector. If wire is okay, check ignition coil resistance (for internal short to ground).

Ignitor Check

Check TDC/CRANK/CYL sensor resistance values. See TACH PULSE SIGNAL . Check power sources. If no problems are found and spark is not present, replace ignitor.

Scheme 2

1. Turn ignition off. Remove distributor cap. Remove 2 Phillips screws retaining primary ignition leads to ignition coil. Remove primary leads from ignition coil. Using an ohmmeter, check resistance between primary terminals "A" and "B" on ignition coil. (Scheme 2) Resistance should be.6-.8 ohms at room temperature.
2. Check secondary resistance between terminal "A" and secondary output terminal (coil tower) at room temperature. See «IGNITION COIL RESISTANCE»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. If readings are not within specification, replace coil. IGNITION COIL RESISTANCE - Ohms@68°F (20°C) Application Primary Secondary Accord.6-.8 12,800-19,2000 TIMING CONTROL SENSOR USAGE Application Sensor/System Accord TDC/CRANK/CYL Sensor

Scheme 3

Scheme 4

1. Timing control and triggering of fuel injectors are based upon input signals from TDC/CRANK/CYL sensors. See «TIMING CONTROL SENSOR USAGE»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. These sensors are simple PM (Permanent Magnet) generator pick-up coils.
2. Using a DVOM on low voltage scale (preferably with a bar-graph function), check for a pulsed low-voltage signal at proper ECU test harness terminals with engine cranking. (Scheme 3) See «ECU TACH SIGNAL & RESISTANCE TEST TERMINALS»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. If a pulsed signal is present, no fault is present. If pulsed signal is not present, check sensor and wiring integrity.
3. To test sensor and wiring integrity, turn ignition off. Disconnect connectors from ECU. Lightly probe appropriate ECU harness terminals to check for proper winding resistance of each sensor. See «ECU TACH SIGNAL & RESISTANCE TEST TERMINALS»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. If resistance is within specification, go to step 5). If resistance is not within specification, check resistance of TDC/CRANK/CYL sensor (if equipped) directly at sensor connector. (Scheme 4)
4. If sensor resistance is now within specification, repair opens, shorts or corrosion in wire harness between sensor(s) and ECU. If resistance is not within specification, replace sensor.
5. If resistance values in step 3) were within specification, check for continuity to ground at each ECU sensor terminal. If continuity is present, disconnect sensor(s) and recheck for continuity to ground at ECU sensor terminals. If continuity no longer exists, go to the next step. If continuity to ground is still present, repair short to ground in ECU harness between ECU and sensor(s).
6. If continuity did not exist with sensor disconnected, check for continuity to ground on each sensor connector. (Scheme 4)and «SENSOR RESISTANCE TEST TERMINALS»(/honda/accord/iv-1989-1993/remont/testing-diagnostics/#engine-controls-basic-testing) table. If continuity to ground exists, replace sensor. ECU TACH SIGNAL & RESISTANCE TEST TERMINALS Application Terminals Ohms CRANK B13 & B14 350-700 CYL B11 & B12 350-700 TDC B15 & B16 350-700 SENSOR RESISTANCE TEST TERMINALS Application Terminal or Wire Color CRANK Blue/Green & Blue/Yellow CYL White & Orange TDC White/Blue & Orange/Blue

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 SPECIFICATIONS (1)

IGNITION TIMING (Degrees BTDC@RPM)

SUMMARY

If no faults were found while performing BASIC TESTING , proceed to G - 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 diagnosis procedures.

See also:
• WIRING DIAGRAMS
• SYSTEM/COMPONENT TESTS
• ADJUSTMENTS
• G - TESTS W/ CODES
• TESTS W/O CODES
• ENGINE COMPRESSION
• RELIEVING FUEL PRESSURE