Engine Controls - Basic Testing: Other Lexus SC I

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. To check engine compression with a compression gauge, bring engine to normal operating temperature. Disconnect distributor electrical connector(s). Disconnect fuel injector connectors. Remove air intake hose from throttle body. Remove all spark plugs. Fully open throttle. Ensure engine cranking speed is at least 250 RPM when measuring compression.

COMPRESSION SPECIFICATIONS

Exhaust System Backpressure (Using Pressure Gauge)

Remove Heated Oxygen Sensor (HO2S). Connect a 0-5 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is more than 1 3/4 - 2 psi (.12-.14 kg/cm 2 ), exhaust system or catalytic converter is plugged.

Exhaust System Backpressure (Using Vacuum Gauge)

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, check for restricted exhaust system.

FUEL SYSTEM

FUEL SYSTEM PRESSURE RELEASE

Remove trunk floor mat. Remove trunk trim panel. Disconnect fuel pump connector. Start and run engine until it stops. Wrap fuel line connection at fuel rail with shop towel to catch any spilled fuel. Loosen banjo bolt enough to relieve any remaining fuel pressure. Tighten banjo bolt.

Using Scan Tester

1. Remove instrument panel fuse box cover. Connect scan tester to Data Link Connector (DLC) No. 3. (Scheme 3) Turn ignition on. DO NOT start engine.
2. Using scan tester manufacturer's instructions, activate electric fuel pump. Listen for fuel pump operating sound and feel for pressure in fuel line near fuel filter. Turn ignition off. Remove scan tester. If fuel pump operates, check fuel pressure. See «FUEL PRESSURE»(ref-22018-S35251660092001010300000).
3. If fuel pump does not operate, EFI main relay, circuit opening relay or fuel pump relay (if used) may be defective. See SYSTEM & COMPONENT TESTING article.
4. If relays are okay, check wiring circuit and fuses. If fuel pump does not operate, check for defective fuel pump or defective fuel pump ground. See appropriate wiring diagram in WIRING DIAGRAMS article.

Scheme 3

Using Battery Voltage

1. Remove trunk floor mat. Remove trunk trim panel. Disconnect fuel pump connector.
2. Connect battery voltage to specified terminals on fuel pump connector to activate fuel pump. (Scheme 4) Listen for fuel pump operating sound and feel for pressure in fuel line near fuel filter. If fuel pump operates, check fuel pressure. See «FUEL PRESSURE»(ref-22018-S35251660092001010300000). Disconnect battery voltage from fuel pump.
3. If fuel pump fails to operate, replace fuel pump. If fuel pump will not operate while trying to start engine, EFI main relay, circuit opening relay or fuel pump relay (if used) may be defective. See SYSTEM & COMPONENT TESTING article.
4. If relays are okay, check wiring circuit, fuses and fuel pump ground. See appropriate wiring diagram in WIRING DIAGRAMS article. Rein-stall electrical connector and remaining components.

Scheme 4

FUEL PRESSURE

1. Ensure battery is fully charged. Turn ignition off. Disconnect negative battery cable. Go to step 3.
2. Disconnect vacuum pipe from rear of air intake chamber (to access fuel hose). Cover fuel inlet hose banjo bolt (at fuel rail) with shop towel. Slowly loosen banjo bolt to relieve fuel pressure. Remove banjo bolt and gaskets. Go to step 5).
3. Install Fuel Pressure Gauge (SST 09268-45012), gaskets and banjo bolt. Tighten banjo bolt. Reconnect negative battery cable. Connect scan tester to Data Link Connector (DLC) No. 3. (Scheme 3)
4. Using scan tester manufacturer's instructions, activate electric fuel pump and note fuel pressure. Fuel pressure should be within specification. See «FUEL PUMP PERFORMANCE»(ref-22018-S21862968122001010300000) table. NOTE: Fuel pump may also be activated by connecting battery voltage to specified terminals on fuel pump. (Scheme 4) FUEL PUMP PERFORMANCE Application Type Tested At Idle W/Vacuum psi (kg/cm 2 ) At Idle W/O Vacuum psi (kg/cm 2 ) Fuel Pump 28-34 (2.0-2.4) 38-44 (2.7-3.1)
5. If fuel pressure exceeds specification, replace fuel pressure regulator. If fuel pressure is less than specified, check for defective fuel lines, connections, fuel pump, fuel filter, fuel pressure regulator or fuel pressure control Vacuum Switching Valve (VSV, if equipped.
6. Remove scan tester from DLC No. 3. Start engine and allow to idle. Disconnect and plug vacuum line at fuel pressure regulator. Note fuel pressure. Reconnect vacuum hose on fuel pressure regulator and note fuel pressure. Fuel pressure should be within specification. See «FUEL PUMP PERFORMANCE»(ref-22018-S21862968122001010300000) 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. 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.
8. Disconnect negative battery cable. Remove fuel pressure gauge. Reinstall banjo bolt using NEW gaskets. Tighten banjo bolt. Install negative battery cable.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. See IDLE SPEED SPECIFICATIONS and IGNITION TIMING tables. Idle speed and ignition timing are not adjustable. For checking procedures, see ON-VEHICLE ADJUSTMENTS article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to SELF-DIAGNOSTICS article. If no hard codes are found in self-diagnostics, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.