Engine Controls - Basic Testing Plymouth Laser I

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 during which the problem reportedly occurred.

Before entering self-diagnostics (if equipped), 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-megaohm 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 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

Exhaust System Backpressure

The exhaust system can be checked with a vacuum gauge or pressure gauge. Remove O2 sensor or air injection check valve (if equipped). Connect a 1-10 psi gauge and run engine at 2500 RPM. If exhaust system backpressure is more than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.

If using a vacuum gauge, connect gauge to intake manifold vacuum, and 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 PUMP OPERATION AND PRESSURE CHECK

Some 1991 Laser and Talon models with 2.0L engines were built without a fuel pump check terminal. To check fuel pressure and fuel pump operation on these models, remove right center console cover. Remove fuel control relay. Connect battery voltage to wiring harness side of control relay terminal No. 2. (Scheme 1) Fuel pump should activate.

Scheme 1

FUEL PRESSURE

Basic diagnosis of fuel system should begin with determining fuel system pressure.

Relieving Fuel Pressure

Disconnect fuel pump wiring harness at fuel tank. Start engine. Let engine run until fuel is exhausted and engine stops. Turn ignition off. Disconnect negative battery cable. Connect fuel pump wiring harness connector.

Checking Fuel Pressure

1. Relieve fuel pressure. On 2.0L and 2.0L Turbo, remove throttle body bracket. On all models, wrap fuel lines with shop towel and disconnect high pressure fuel line at fuel rail. Install Adapters (MD998709 and MD998742) between fuel rail and high pressure fuel line. Connect fuel pump pressure gauge.
2. Connect negative battery cable. Apply battery voltage to fuel pump check terminal to activate fuel pump. (Scheme 2) Check for fuel leaks. Disconnect battery voltage from check terminal. Start engine and let idle.
3. Measure fuel pressure with fuel pressure regulator vacuum hose disconnected. Measure fuel pressure with fuel pressure regulator vacuum hose connected. See FUEL PRESSURE SPECIFICATIONS table.
4. Increase engine speed to 2500-3000 RPM 2-3 times. Ensure fuel pressure does not drop when engine returns to idle. Check for fuel pressure in fuel return hose by gently pinching hose (with hand) while raising engine speed. There will not be any fuel pressure in return hose if fuel volume is low.
5. If fuel pressure is too low during test, check for clogged fuel filter, faulty fuel pressure regulator or faulty fuel pump. If fuel pressure is too high, check for bent or clogged fuel return hose or faulty fuel pressure regulator.
6. If fuel pressure is the same when fuel pressure regulator vacuum hose is connected and disconnected, check for clogged or broken fuel pressure regulator vacuum hose or faulty fuel pressure regulator.
7. Stop engine and check for change in fuel pressure. Fuel pressure should not drop. If fuel pressure drops slowly after engine is stopped, replace fuel injector. If fuel pressure drops immediately after engine is stopped, replace fuel pump.

Note. Some 1991 Laser and Talon models with 2.0L engines were built without a fuel pump check terminal. To check fuel pressure and fuel pump operation on these models, remove right center console cover. remove control relay. Connect battery voltage to wire harness side of control relay terminal No. 2. (Scheme 2) Fuel pump should activate. For further information please refer to T.S.B. No. 08-18-91.

FUEL PRESSURE SPECIFICATIONS

Scheme 2

FUEL INJECTOR OPERATING CHECK

Using a stethoscope, check injector operating sound during engine cranking and idling. Ensure operational sound increases as engine RPM is increased.

FUEL INJECTOR RESISTANCE CHECK

Disconnect fuel injector connector. Using an ohmmeter, measure fuel injector resistance. On 1.8L and 2.0L, resistance should be 13-16 ohms at 68°F (20°C). On 2.0L Turbo, resistance should be 2-3 ohms at 68°F (20°C). If resistance is incorrect, replace fuel injector.

CONTROL RELAY

Note. Control relay failure prevents power supply to fuel pump, injectors and engine control unit, resulting in no-start failure. When testing control relay, damage to relay may result if battery voltage is applied to wrong terminals.

1.8L

1. Remove control relay from vehicle. Control relay is located on right side of center console. Disconnect control relay connector. Using an ohmmeter, check for approximately 95 ohms of resistance between control relay terminals No. 3 and 5, and terminals No. 2 and 5. (Scheme 3)
2. Using an ohmmeter, ensure approximately 35 ohms of resistance is present between control relay terminals No. 6 and No. 7. Ensure there is infinite resistance between terminals No. 1 and No. 4, and between terminals No. 2 and No.4.
3. Connect positive ohmmeter lead to terminal No. 6 and negative lead to terminal No. 8. Ensure there is infinite resistance. Using an ohmmeter, connect positive ohmmeter lead to terminal No. 8 and negative lead to terminal No. 6. Zero ohms resistance should exist.
4. While grounding terminal No. 6 and applying battery voltage to terminal No. 8, ensure there is zero ohms resistance between terminals No. 2 and 4.
5. While grounding terminal No. 6 and applying battery voltage to terminal No. 7, ensure there is zero ohms resistance between terminals No. 1 and 4. Replace control relay if it does not test as described.

Scheme 3

2.0L & 2.0L Turbo

1. Remove control relay from vehicle. Control relay is located on right side of center console. Disconnect control relay connector.
2. While applying battery voltage to control relay terminal No. 10, ensure battery voltage is not present at terminals No. 4 and No. 5. (Scheme 4) While applying battery voltage to terminal No. 10 and grounding terminal No. 8, ensure battery voltage is present at terminals No. 4 and No. 5.
3. While grounding terminal No. 6, ensure continuity is not present at terminals No. 2 and No. 3. While applying battery voltage to terminal No. 9 and grounding terminal No. 6, ensure continuity is present at terminals No. 2 and No. 3.
4. Apply battery voltage to terminal No. 3. Ensure there is no voltage at terminal No. 2. While applying battery voltage to terminal No. 3 and grounding terminal No. 7, battery voltage should be present at terminal No. 2. Replace control relay if it does not test as described.

Scheme 4

IGNITION CHECKS

Note. The 1.8L engine uses an optical ignition system. The 2.0L and 2.0L Turbo use a Direct Ignition System (DIS).

Spark Test

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 not be greater than specification. See HIGH TENSION WIRE RESISTANCE table.

Ignition Coil Resistance

Disconnect ignition coil connector. Measure primary coil resistance between ignition coil terminals. (Scheme 5) Primary coil resistance should be.9 - 1.1 ohms at 68°F (20°C). Measure secondary coil resistance between a primary coil terminal and secondary coil terminal. Secondary resistance should be 19,000-27,000 ohms.

HIGH TENSION WIRE RESISTANCE

Scheme 5

Power Transistor

1. Connect analog ohmmeter leads between power transistor terminals No. 5 and No. 8. Ensure ohmmeter negative lead is connected to terminal No. 8. Ohmmeter should indicate no continuity.
2. Using a 1.5-volt dry cell battery, connect positive battery lead to power transistor terminal No. 6 and negative lead to terminal No. 5. (Scheme 6) When battery is connected, ohmmeter should indicate continuity.

Scheme 6

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 greater than specification. See HIGH TENSION WIRE RESISTANCE table.

1. Disconnect ignition coil connector. Measure primary coil resistance between ignition coil terminals No. 1 and No. 3. Also measure resistance between ignition coil connector terminals No. 2 and No. 3. (Scheme 7) Primary resistance should be.77-.95 ohms at 68°F (20°C).
2. Measure secondary coil resistance between high voltage tower terminals for No. 1 and No. 4 cylinders, and between high voltage tower terminals for No. 2 and No. 3 cylinders. (Scheme 7) Secondary resistance should be 10,300-13,900 ohms. Replace ignition coil if it does not test as described.

Scheme 7

1. Connect analog ohmmeter leads between power transistor terminals No. 3 and No. 7. Ohmmeter should indicate no continuity. Using a 1.5-volt dry cell battery, connect positive battery lead to power transistor terminal No. 3 and negative lead to terminal No. 6. (Scheme 8) When battery is connected, ohmmeter should indicate continuity.
2. Connect ohmmeter between power transistor terminals No. 1 and No. 3. Ohmmeter should indicate no continuity. Connect dry cell battery positive lead to power transistor terminal No. 2 and negative lead to terminal No. 3. (Scheme 8) When battery is connected, ohmmeter indicate continuity. Replace power transistor if it does not test as described.

Scheme 8

IDLE SPEED & IGNITION TIMING

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

SUMMARY

If no faults are found while performing tests in this article, proceed to appropriate G - TESTS W/ CODES article. If no hard codes are found 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 diagnosis procedures.

See also:
• HIGH TENSION WIRE RESISTANCE