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GLYPH<3> F - BASIC TESTING

GLYPH<3> 1995 Volvo 850

1995 ENGINE PERFORMANCE Volvo - Basic Diagnostic Procedures

850

INTRODUCTION

NOTE: In this article, Engine Control Module (ECM) may also be referred to as Engine Control Unit (ECU).

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 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 using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless otherwise instructed in test procedure.

PRELIMINARY INSPECTION & ADJUSTMENTS

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 not pinched or cut. See M - VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

MECHANICAL INSPECTION

Compression

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

WARNING: 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 engine oiling system.

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COMPRESSION SPECIFICATIONS TABLE /a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0

Application Specification (Minimum)

Compression Pressure ....... 189-219 psi (13.2-15.3 kg/cm ) /a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0✁/a0

• 1. Exhaust system can be checked using a vacuum or pressure gauge. Remove oxygen sensor or air injection check valve (if equipped).
• 2. 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, exhaust system or catalytic converter is plugged.
• 3. If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steadily. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.

FUEL SYSTEM

WARNING: Always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.

FUEL PRESSURE

Fuel Pressure

• 1. Before disconnecting, cover fuel line connector using shop towel to absorb any fuel spray. Connect Fuel Pressure Gauge (5011) between fuel line and fuel rail. Seal free end of hose using Plug (5266) or use Fuel Drainage Unit (981 2270, 2273 and 2282).
• 2. Lift cover on central electrical unit located in engine compartment and remove fuel pump relay. See Fig. 1.
• 3. Connect a jumper wire between relay terminals No. 1 and 3. See Fig. 2.

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• 4. Turn ignition on. Fuel pump should start. Fuel filler cover can be removed to determine whether main pump is operating. Fuel pressure should be about 43.5 psi (3.06 kg/cm ). If pressure is too low, pinch return hose by hand and check whether pressure rises. DO NOT allow pressure to exceed 86 psi (6 kg/cm ).

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• 5. If pressure rises rapidly, pump and lines are okay. Replace pressure regulator and recheck line pressure. If pressure rises slowly, fuel filter, fuel pump strainer or fuel lines are blocked. If pressure does not rise, fuel pump is probably faulty.
• 6. If pressure is too high, remove jumper wire between relay or fuse terminals. Remove return hose from pressure regulator. Blow in pipe. Remove vacuum hose from pressure regulator. Blow in pipe. If both hoses are open, pressure regulator is defective. Replace regulator and recheck pressure.

Fig. 2: Identifying Fuel Pump Relay Terminals Courtesy of Volvo Cars of North America.

CAUTION: Ensure ignition is off when connecting or disconnecting ECU connector.

Fuel Pump Circuit 1) If fuel pump does not operate with ignition on, remove fuel pump relay. See Fig. 1. Connect jumper wire between fuel pump relay terminals No. 1 and 3. See Fig. 2. Turn ignition on. If fuel pump does not start, go to next step. If fuel pump starts, replace

• fuel pump relay. 2) Turn ignition off. To check relay ground, connect ohmmeter between ground and fuel pump relay terminal No. 2. See Fig. 2. Ohmmeter should indicate about zero ohms. If ohmmeter does not indicate about zero ohms, check wiring between fuel pump relay and ground.

• 3. To check fuel pump relay voltage supply, connect voltmeter between ground and fuel pump relay terminal No. 1. See Fig. 2 . Turn ignition on. Battery voltage should be present. If battery voltage is not present, check wiring between fuel pump relay and fuse No. 2.
• 4. Turn ignition off. Connect ohmmeter between ground and relay terminal No. 3. See Fig. 2. About 1.5 ohms should be present. If about 1.5 ohms