Engine Controls - Basic Testing: Diagnosis Lexus SC I

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.

MECHANICAL INSPECTION

SPARK TEST

1. Disconnect coil wire from distributor(s). Using insulated pliers, hold end of coil wire 1/2" from ground. Crank engine for 1-2 seconds. If spark is not present, go to next step. If spark is present at coil wire but not at spark plug wire, replace faulty distributor rotor, cap, wires or spark plugs as necessary.
2. Turn ignition off. Check for poor electrical connections at ignition coil, ignitor and distributor. Repair as necessary. If connections are okay, check resistance of coil wire and spark plug wires. Maximum allowable resistance is 25,000 ohms per wire.
3. If resistance is okay, turn ignition on. Disconnect ignition coil connector. Measure voltage between ground and positive terminal at ignition coil connector. See «IGNITION COIL POSITIVE TERMINAL IDENTIFICATION»(ref-22018-S38791430822001010300000) table. If battery voltage is not present, check for open or grounded wire between battery and ignition coil or open fuse, also check for faulty ignition main relay).
4. If battery voltage is present, turn ignition off. Measure ignition coil resistance. To measure primary resistance, measure resistance between terminals of ignition coil. To measure secondary resistance, measure resistance between positive wire terminal at ignition coil and coil secondary tower. If resistance is not as specified, replace ignition coil. See «IGNITION COIL RESISTANCE»(ref-22018-S10946700532001010300000) table. IGNITION COIL POSITIVE TERMINAL IDENTIFICATION Application Wire Color Ignition Coil Black/Orange IGNITION COIL RESISTANCE - Ohms Application Primary Secondary Ignition Coil Resistance Cold (1).21-.33 6400-11,100 Hot (2).27-.39 8200-13,000 (1) Coil temperature of 14-122°F (-10-50°C). (2) Coil temperature of 123-212°F (51-100°C).
5. If resistance is as specified, check resistance across terminals of the following distributor sensor. Distributor pick-up coil. (Scheme 1) Camshaft Position (CMP) sensor and Crankshaft Position (CKP)
6. If resistance is not as specified, replace distributor housing (CMP sensor See «DISTRIBUTOR SENSOR RESISTANCE»(ref-22018-S37058882462001010300000) table. If resistance is as specified, Go to next step.
7. Measure air gap of pick-up coils G1, G2 and NE. (Scheme 2) See DISTRIBUTOR PICK-UP COIL AIR GAP table. If air gap is within specification, go to next step. If air gap is not within specification, replace distributor.
8. Check ignition IGT signal from Engine Control Module (ECM). If ignition Check for ignitor circuit malfunction (IGT signal). If IGT signal from ECM is defective a Diagnostic Trouble Code (DTC) should set in ECM memory. See testing procedure for DTC P1300 in SELF-DIAGNOSTICS article. If IGT signal circuit is okay, substitute another ignitor and recheck system operation.

DISTRIBUTOR SENSOR RESISTANCE

DISTRIBUTOR PICK-UP COIL AIR GAP (1)

Scheme 1

Scheme 2