Engine Controls - Basic Testing Lexus LS 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 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.

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 the engine's oiling system.

ENGINE COMPRESSION

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 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

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

Scheme 1

Scheme 2

Scheme 3

1. Check fuel pressure. Ensure a sufficient amount of fuel is in fuel tank. Turn ignition off. Locate check connector. (Scheme 1)or (Scheme 2). Using a jumper wire, connect check connector terminals +B and FP. (Scheme 3) Turn ignition on.
2. Using fingers, ensure fuel pressure is felt in hose from fuel filter. When fuel system is pressurized, fuel return noise will also be heard. Turn ignition off.
3. If no fuel pressure was felt, check fusible links, fuses (EFI 15-amp and IGN 7.5-amp), EFI main relay, fuel pump, ECU and wiring connections. CAUTION: SLOWLY loosen cold start injector fuel line to avoid fuel spraying onto skin, eyes and vehicle finish.
4. Connect fuel pressure gauge to cold start injector fuel line. Using a jumper wire, connect terminals FP and +B of check connector. (Scheme 3) Turn ignition on. Check fuel pressure.
5. See FUEL PRESSURE SPECIFICATIONS TABLE. If fuel pressure is more than specification, replace fuel pressure regulator. If fuel pressure is less than specification, check fuel hoses, hose connections, fuel pump, fuel filter and fuel pressure regulator. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. FUEL PRESSURE SPECIFICATIONS Application psi (kg/cm 2 ) Ignition On, Engine Off 38-44 (2.7-3.1) Engine Idling (1) 38-44 (2.7-3.1) Engine Idling (2) 33-37 (2.3-2.6) Ignition Off, Engine Off 21 (1.5) (1) With fuel pressure regulator vacuum hose disconnected. (2) With fuel pressure regulator vacuum hose connected. CAUTION: DO NOT confuse check connector terminal connection as this may create additional malfunctions.
6. Start engine. Disconnect and plug vacuum hose from fuel pressure regulator. Check fuel pressure. See FUEL PRESSURE SPECIFICATIONS TABLE Unplug and reconnect vacuum hose to fuel pressure regulator.
7. Check fuel pressure. See FUEL PRESSURE SPECIFICATIONS TABLE. If fuel pressure is not within specification, check fuel pressure regulator and vacuum hose.
8. Turn engine off. Ensure fuel pressure does not drop to less than specified value for 5 minutes after engine is turned off. See FUEL PRESSURE SPECIFICATIONS TABLE.
9. If fuel pressure is not as specified, check fuel pump, fuel pressure regulator and fuel injectors. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Remove fuel pressure gauge.

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

1. On all models, check for spark. Remove coil wire from distributor. Using insulated pliers, hold end of coil wire 1/2" from ground. Crank engine. If spark is present, see ES250 DIAGNOSIS BY SYMPTOM or LS400 DIAGNOSIS BY SYMPTOM in TESTS W/O CODES article in the ENGINE PERFORMANCE Section. If spark is not present, go on to step 2).
2. Turn ignition off. Check ignition coil, ignitor and distributor connectors. Repair as necessary. If connectors are okay, go to next step.
3. Using an ohmmeter, check resistance of high tension cables. Maximum resistance allowed is 25,000 ohms per cable. Replace as necessary. If resistance is within specification, go to next step.
4. Turn ignition on. Using a DVOM, ensure battery voltage is present at ignition coil positive terminal. If battery voltage is not present, check wiring between ignition switch and ignition coil. If battery voltage is present, go to next step. NOTE: LS400 has 2 ignition coils.
5. Turn ignition off. Using a DVOM, measure resistance of ignition coil (cold). Primary resistance is.40-.50 ohm. Positive terminal on ignition coil has a tab next to terminal. Secondary resistance is 10,200-13,800 ohms. If resistance is not within specification, replace ignition coil. If resistance is within specification, go to step 6) for ES250 or step 9) for LS400.
6. On ES250, measure resistance of pick-up coil. (Scheme 4) Measure resistance between terminals G1 and G, G2 and G, and NE and G. Resistance should be 205-255 ohms. If resistance is not within specification, replace distributor housing assembly.
7. Check air gap in distributor. Measure air gap of G1 pick-up, G2 pick-up and NE pick-up. (Scheme 5) Air gap specification is.008-.016" (.20-.40 mm). If air gap is not to specification, replace distributor.
8. Perform CODE 14 (step 9) trouble shooting procedures for ES250. See TESTS W/CODES article in the ENGINE PERFORMANCE Section. If voltage reading and wiring harness are okay, try another ignitor.
9. On LS400 models, using an ohmmeter, measure resistance of No. 1 cam position sensor. (Scheme 6) Resistance specification is 950-1250 ohms. If No. 1 cam position sensor resistance is not to specification, replace sensor. If resistance is within specification, go to next step.
10. Using an ohmmeter, measure resistance of No. 2 cam position sensor. (Scheme 7) Resistance specification is 950-1250 ohms. If No. 2 cam position sensor resistance is not to specification, replace sensor. If resistance is within specification, go to next step.
11. Using an ohmmeter, measure resistance of engine speed sensor. (Scheme 8) Resistance specification is 950-1250 ohms. If engine speed sensor resistance is not to specification, replace sensor. If resistance is within specification, go to next step.
12. Perform CODE 14 and CODE 15 (step 5) diagnostic procedures for LS400. See TESTS W/CODES article in the ENGINE PERFORMANCE Section. Reading should be approximately battery voltage.
13. If voltage reading is okay, try another ignitor. If voltage reading is not within specification in CODE 14 and CODE 15 (step 5), continue with diagnostic procedures for CODE 14 and CODE 15.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

Note. Ensure tachometer is compatible with this system before use.

IDLE SPEED SPECIFICATIONS

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.