Engine Controls - Basic Testing Mazda 929 HD

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, looking 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 VACUUM DIAGRAMS article in the ENGINE PERFORMANCE section 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.

COMPRESSION SPECIFICATIONS

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. Remove O2S sensor or air injection check valve (if equipped). Connect a 0-5 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 (FUEL INJECTION)

Fuel Pressure

1. Disconnect circuit opening relay. See CIRCUIT OPENING RELAY LOCATIONS table.
2. To bleed down fuel in system, start engine (if possible) and allow to die. Connect pressure gauge to fuel line at fuel filter. Reconnect circuit opening relay.
3. Turn ignition on. Jump test connector terminals Fp and ground. If pump does not run, check fuel pump circuit and circuit opening relay.
4. If possible, start engine. Check fuel pressure with vacuum connected to and disconnected from pressure regulator. See «REGULATED FUEL PRESSURE»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table. Turn engine off and disconnect jumper wire at fuel pump check connector. Wait 10 minutes and ensure residual pressure is at least 21 psi (1.5 kg/cm 2 ).
5. Operate fuel pump by jumpering fuel pump test connector. Check fuel pump performance. Pinch hose between pressure gauge and fuel filter. DO NOT hold longer than necessary to check pressure. See «FUEL PUMP PERFORMANCE»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table. If pump does not meet specifications, check fuel pump circuits, fuel pump, fuel tank, fuel filter and repair or replace as necessary.

FUEL PUMP PERFORMANCE

REGULATED FUEL PRESSURE

Note. Fuel pump control unit terminal identification is not available.

Fuel Pump Circuit

1. Turn ignition on. Attach jumper wire to test connector terminal Fp and to ground in the diagnostic connector, next to battery.
2. Listen for fuel pump operating sound. If there is no sound, check main fuse, circuit operating relay, fuel pump and all electrical connections. PCM grounds circuit opening relay and operates fuel pump whenever distributor or crank angle sensor signals are present.
3. If circuit opening relay does not work, proceed to «SYSTEM/COMPONENT TESTS»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) article in the ENGINE PERFORMANCE section or «TESTS W/CODES»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-tests-wcodes) article in the ENGINE PERFORMANCE section.

Circuit Opening Relay

1. With relay connected, ensure battery voltage is present at relay terminal Black/White wire. For locations of circuit opening relay, see «CIRCUIT OPENING RELAY LOCATION»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table.
2. If voltages are okay, remove relay from vehicle. Using a 12-volt battery source, connect 12 volts to relay terminals "A" and "B". Ensure continuity is present across terminals "C" and "D". If continuity is not as specified, replace circuit opening relay.

CIRCUIT OPENING RELAY LOCATION

CIRCUIT OPENING RELAY CIRCUIT VOLTAGE

SPARK CHECK

Check for spark at coil wire and at each spark plug wire using a high output spark tester. Check spark plug wire resistance on suspect wires. Resistance should be no less than 4878 ohms per foot.

IGNITION COIL POWER SOURCE

Turn ignition on. Using voltmeter, check for 12 volts between positive (+) terminal and ground. If no voltage is present, check battery feed, main fuse, EGI main relay (RX7), ignition switch and fusible links.

IGNITION COIL RESISTANCE

1. Remove primary and secondary leads from ignition coil. Using ohmmeter, check primary resistance between positive and negative terminals of coil. (Scheme 1) Resistance should be as specified in «IGNITION COIL RESISTANCE»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table. If resistance is not as specified, replace ignition coil.
2. Check secondary resistance between (positive) terminal and coil tower. (Scheme 1) See «IGNITION COIL RESISTANCE»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table. If resistance is not within specification, replace coil.

Scheme 1

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

CRANK ANGLE SENSOR RESISTANCE

1. Disconnect crank angle sensor connector. Crank angle sensor is a separate unit located at front of crankshaft. Measure resistance between terminals. (Scheme 2) If resistance is not as indicated, replace crank angle sensor.
2. If ignition coil resistance and crank angle sensor test okay, check for spark. If spark is still not present, go to HALL-EFFECT SENSORS test procedure.

CRANK ANGLE SENSOR RESISTANCE

Scheme 2

HALL-EFFECT SENSORS

1. Remove distributor. Remove circuit opening relay and disconnect 3-pin connector from distributor. This will prevent coil sparking. Turn ignition on.
2. Using a voltmeter, backprobe power wire and ground wire at distributor. Voltmeter should display 12 volts. If voltage is not as specified, check ignition and ground circuits. Backprobe sensor wire at distributor. See «HALL-EFFECT SENSOR VOLTAGE SPECIFICATIONS»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table for wire colors. Slowly rotate distributor shaft one turn. Voltmeter should pulse 0-5 volts 4 times (4-cylinder) or 6 times (V6).
3. Backprobe wire at distributor. See «HALL-EFFECT SENSOR VOLTAGE SPECIFICATIONS»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table for wire colors. Slowly rotate distributor shaft one turn. Voltmeter should pulse 0-5 volts one time. If either sensor does not work as described, turn ignition off. Disconnect 4-pin or 6-pin connector at distributor.
4. Turn ignition on. Ensure 5 volts are present at same wires which were checked in steps 2) and 3). If 5 volts are not present, check wiring and PCM. If 5 volts are present, replace distributor assembly.

HALL-EFFECT SENSOR VOLTAGE SPECIFICATIONS

IGNITOR

1. Ensure coil and power source are okay before checking ignitor. Disconnect coil ignitor connector. Install Ignitor Checker (49 F018 002) and Adapter Harness (N018 001). Connect the ignitor checker and adapter between the ignitor and wiring harness, connect the power leads to the battery.
2. Turn ignition on. Disconnect the high-tension coil lead from the distributor and hold it about 1/4" from ground. Flip the SW2 on and off, and verify a strong Blue spark is discharged from lead. If spark is weak in color, replace the coil. If no spark is present, check battery feed, main fuse, ignition switch and fusible links. Repair or replace as necessary. CAUTION: DO NOT hold the SW2 switch on longer than one second or igniter will be damaged.
3. Turn ignition on. Using voltmeter, check voltage on Black wire of adapter harness. Flip SW2 switch on and off. Verify voltmeter fluctuates. If voltmeter does not fluctuate, replace ignitor and retest.

1. Turn ignition off. Disconnect ignitor connector and install Test Harness (49 N018 001). Using a needle-type ohmmeter, connect (+) lead to ground and (-) lead to single-pin test wire of test harness. (Scheme 3) CAUTION: Ensure ohmmeter is installed with (+) lead to ground and (-) lead to single-pin wire of test harness. DO NOT reverse leads or damage may result.
2. Connect Ignitor Checker (49 H018 910) to other lead of test harness and to battery. Set ohmmeter to X1 scale.
3. Turn ignition on. DO NOT touch ignitor checker SW1 switch. Push up ignitor checker SW2 switch and note ohmmeter reading. Ohmmeter needle should jump to 1/2 of the scale and then return. If ohmmeter does not operate as specified, replace ignitor.

Scheme 3

IDLE SPEED & IGNITION TIMING

Ensure idle speed and base ignition timing are set to specification. If necessary, ADJUSTMENTS article in the ENGINE PERFORMANCE section.

IGNITION TIMING SPECIFICATIONS

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to 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.

See also:
• SYSTEM/COMPONENT TESTS
• TESTS W/CODES
• ADJUSTMENTS
• TESTS W/O CODES
• REGULATED FUEL PRESSURE