Engine Controls - Basic Testing - 4-cyl Toyota Tercel L40

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 this 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.

4-CYLINDER COMPRESSION SPECIFICATIONS

Exhaust System Backpressure

The 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 2 psi, 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 SYSTEM

Basic diagnosis of fuel system should begin by checking fuel pump operation and then fuel pressure.

FUEL PUMP OPERATION

1. Install jumper wire between +B and FP terminals of engine check connector. (Scheme 1)-7. Turn ignition on.
2. Listen for fuel pump operating sound and feel for pressure in fuel line near the fuel filter. Turn ignition off. Remove jumper wire. If fuel pump operates, check fuel pressure. See «FUEL PRESSURE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl__fuel-pressure) under FUEL SYSTEM.
3. If fuel pump does not operate, connect a jumper wire from battery source to FP terminal of engine check connector. If fuel pump operates, the EFI main relay, circuit opening relay or fuel pump relay may be defective. For explanation of relay operation, see «FUEL PUMP CONTROL CIRCUIT»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) under FUEL SYSTEM.
4. If relays are okay, check wiring circuit and fuses. If fuel pump does not operate, check for defective fuel pump or open circuit between engine check connector and fuel pump, defective fuel pump ground or fuses. See appropriate wiring diagram in WIRING DIAGRAMS article in this section.

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FUEL PRESSURE

Note. All models use in-tank fuel pump. Fuel pump contains internal relief valve and check valve.

1. Ensure battery is fully charged and ignition is off. Disconnect negative battery cable. Disconnect electrical connector from cold start injector (if equipped). Place container under cold start injector pipe or deliver pipe.
2. Note location of fuel pressure gauge installation. (Scheme 8)-15. Cover union bolt with shop towel and slowly loosen union bolt to relieve fuel pressure. Remove union bolt and gaskets. Install Fuel Pressure Gauge (SST 09268-45012), using NEW gaskets. (Scheme 8)-15.
3. Tighten union bolt. Reconnect negative battery cable. Install jumper wire between +B and FP terminals of engine check connector. (Scheme 8)-15. Turn ignition on and note fuel pressure. Fuel pressure should be within specification. See «FUEL PUMP PERFORMANCE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table.
4. If fuel pressure is greater than specification, replace fuel pressure regulator. If fuel pressure is less than specification, check for defective fuel lines, connections, fuel pump, fuel filter or fuel pressure regulator.
5. Remove jumper wire from engine check connector. Start engine and allow to idle. Disconnect and plug vacuum line at fuel pressure regulator. Note fuel pressure.
6. Reconnect vacuum hose on fuel pressure regulator and note fuel pressure. Fuel pressure should be within specification. See «FUEL PRESSURE SPECIFICATIONS»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table.
7. If fuel pressure is not within specification, check for defective vacuum hose or fuel pressure regulator. Shut engine off and note fuel pressure.
8. Fuel pressure should hold at least 21 psi (1.5 kg/cm 2 ) for a minimum of 5 minutes. If fuel pressure does not hold as specified, check for defective fuel pump, fuel injector or fuel pressure regulator.
9. Disconnect negative battery cable. Remove fuel pressure gauge. Reinstall union bolt using NEW gaskets. Tighten union bolt. Install cold start injector electrical connector (if equipped). Install negative battery cable.

FUEL PUMP PERFORMANCE

FUEL PRESSURE SPECIFICATIONS

Note. For more information on checking fuel injectors and other fuel sub-systems, see I - SYS/COMP TESTS article in this section.

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EFI Main Relay

1. The EFI fuse supplies constant battery voltage to EFI main relay. EFI main relay provides battery voltage to +B terminal of circuit opening relay and engine check connector.
2. Depending on model, EFI main relay may either be turned on directly by ignition switch or by M-REL terminal of Electronic Control Unit (ECU).
3. Fuel pump should operate with jumper wire between +B and FP terminals of engine check connector and ignition on. If fuel pump does not operate, check EFI main relay and wiring circuit. See I - SYS/COMP TESTS article in this section for testing of EFI main relay. See WIRING DIAGRAMS article in this section for wiring circuit.

Circuit Opening Relay

1. Circuit opening relay controls fuel pump circuit. The Electronic Control Unit (ECU) receives an input signal at STA terminal when engine is cranking. Starter signal is also applied to terminal STA of circuit opening relay.
2. Starter signal energizes circuit opening relay during cranking. The circuit opening relay then provides voltage to the fuel pump or fuel pump relay. Fuel pump relay is used on Celica 2.0L Turbo, MR2 2.0L Turbo and.
3. On all models except Camry 2.2L, Celica, Corolla, MR2, Paseo, and Tercel, fuel pump switch in airflow meter provides the ground for circuit opening relay. On all other models, circuit opening relay is grounded by the ECU through the FC terminal.

Fuel Pump Relay & Fuel Pump Resistor (Celica 2.0L Turbo, MR2 2.0L Turbo)

Fuel pump relay receives voltage from circuit opening relay and operates the fuel pump. Fuel pump operating speed may be varied based on intake air volume and engine RPM signal by the ECU. When ECU grounds fuel pump relay, relay contacts close and voltage is now supplied through fuel pump resistor to fuel pump, changing fuel pump operating speed.

Note. For more information on testing relays and fuel system components, see I - SYS/COMP TESTS article in this section.

SPARK TEST

Note. Before performing spark test, ensure ignitor is properly grounded.

1. On Camry 2.2L, Celica 1.6L (4A-FE), Corolla, Paseo and Tercel models, disconnect spark plug wires. Remove spark plugs. Install spark plug on each spark plug wire. Ground spark plug against cylinder block.
2. On all other models, disconnect high tension coil wire from distributor. Hold coil wire approximately 1/2" away from cylinder block. CAUTION: To prevent gasoline from being injected, DO NOT crank engine for longer than 2 seconds.
3. On all models, crank engine and check for spark. If spark does not occur, check ignition coil, ignitor and distributor connections.
4. If connections are good, using ohmmeter, check resistance of high tension wires. Replace high tension wires if resistance is not within specification. See «HIGH TENSION WIRE RESISTANCE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table. If resistance is within specification, proceed to step 5). HIGH TENSION WIRE RESISTANCE Application Maximum Ohms All Models 25,000 Per Wire
5. Check voltage at ignition coil and ignitor. Turn ignition on. Ensure voltage exists at ignition coil positive terminal. If voltage exists, proceed to step 6). If voltage does not exist, check wiring between ignition switch, ignition coil and ignitor. See WIRING DIAGRAMS article in this section for wiring circuit.
6. Check ignition coil resistance. See «IGNITION COIL RESISTANCE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl__ignition-coil-resistance) under IGNITION CHECKS. Replace ignition coil if resistance is not within specification. If coil resistance is within specification, proceed to step 7).
7. Check pick-up coil resistance. See «PICK-UP COIL RESISTANCE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl__pick-up-coil-resistance) under IGNITION CHECKS. Replace pick-up coil or distributor assembly if pick-up coil resistance is not within specification. If pick-up coil resistance is within specification, proceed to step 8).
8. Check pick-up coil air gap. See «PICK-UP COIL AIR GAP»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl__pick-up-coil-air-gap) under IGNITION CHECKS. If pick-up coil air gap is incorrect, replace distributor assembly. If air gap is correct, proceed to step 9).
9. Check ignition IGT signal from ECU. See appropriate CODE 14 chart in appropriate TESTS W/CODES article in this section. If IGT signal is okay, replace ignitor.

IGNITION COIL RESISTANCE

1. Disconnect wiring from ignition coil so ignition coil is isolated from the system. Using ohmmeter, check primary resistance between ignition coil positive (+) and negative (-) terminals. (Scheme 16)-20.
2. Check secondary resistance between ignition coil positive (+) terminal and high tension wire terminal (coil wire tower). (Scheme 21)-25. Replace ignition coil if resistance is not within specification. See «IGNITION COIL RESISTANCE»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table.

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

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PICK-UP COIL RESISTANCE

1. Note pick-up coil terminal identification on the distributor. (Scheme 26)-32. Using ohmmeter, measure resistance between specified terminals and ensure resistance is within specification. See «PICK-UP COIL RESISTANCE SPECIFICATIONS»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table.
2. Replace distributor assembly if pick-up coil resistance is not within specification.

PICK-UP COIL RESISTANCE SPECIFICATIONS

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PICK-UP COIL AIR GAP

1. Using a flat, non-magnetic feeler gauge, check air gap between signal rotor and pick-up coil projection. (Scheme 33)-40.
2. Replace distributor assembly if pick-up coil air gap is not within specification. See «PICK-UP COIL AIR GAP SPECIFICATIONS»(/toyota/tercel/l40-1990-1994/remont/testing-diagnostics/#engine-controls-basic-testing-4-cyl) table.

PICK-UP COIL AIR GAP SPECIFICATIONS

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IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in this section.

SUMMARY

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

See also:
• FUEL PRESSURE
• FUEL PUMP CONTROL CIRCUIT
• IGNITION COIL RESISTANCE
• PICK-UP COIL RESISTANCE
• PICK-UP COIL AIR GAP