Engine Controls - Basic Testing - 7.4L: Diagnosis Chevrolet Suburban K1500

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. If necessary, see VACUUM DIAGRAMS - 7.4L article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM. Note gauge. Exhaust system is restricted if reading exceeds 1.25 psi (.09 kg/cm 2 ).
2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exists, check for restricted catalytic converter. Replace as required.

General Inspection

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and improper connections. See underhood emission control information label. Check ignition wires for cracks, hardness, and improper connections at distributor cap and spark plugs.
3. Remove spark plugs. Check and replace if necessary.
4. Remove distributor cap and check for moisture, dust, cracks, burns, and arcing to ground through coil mounting screws or rotor.
5. Try to turn distributor shaft by hand. Drive gear pin may be broken.
6. If vehicle has been exposed to very cold temperatures, ensure oil is of proper viscosity and not contaminated with gasoline.

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and improper connections. See underhood emission control information label. Check ignition wires for cracks, hardness, and improper connections at distributor cap and spark plugs.
3. Remove spark plugs. Check and replace if necessary.
4. Remove distributor cap and check for moisture, dust, cracks or burns. Try to turn distributor shaft by hand. Drive gear pin may be broken.
5. If vehicle has been exposed to very cold temperatures, ensure oil is of proper viscosity and not contaminated with gasoline.

FUEL SYSTEM PRESSURE TEST

Diagnostic circuit check determines the following

1. Whether Malfunction Indicator Light (MIL) works.
2. Whether ECM/PCM/VCM/VCM-A is operating and can recognize a fault.
3. Whether any codes are stored.

After performing basic diagnostic procedures listed under PRELIMINARY INSPECTION & ADJUSTMENTS; A-7, BASIC FUEL SYSTEM CHECKS and C-4, BASIC IGNITION SYSTEM CHECKS, use self-diagnostic system for determining computer-related problems. see scheme 4

If codes are NOT indicated and driveability problems still exist after performing necessary tests in diagnostic circuit check, see TESTS W/O CODES - GASOLINE article and SCAN TESTER USAGE under SELF-DIAGNOSTIC SYSTEM in TESTS W/CODES - 7.4L article.

1. Check MIL operation. Turn ignition on with scan tester not connected, DLC terminal not grounded and engine not running. MIL should be on steadily. If light glows and stays on steadily, go to next step. If light does not glow, go to A-1, MALFUNCTION INDICATOR LIGHT (MIL) INOPERATIVE. If light flashes, go to step 3).
2. Ground DLC test terminal "B". MIL should flash Code 12, followed by any codes stored in PCM memory. If light goes from bright to dim or if light remains on and does not flash Code 12, see A-2, MALFUNCTION INDICATOR LIGHT (MIL) ALWAYS ON OR WON'T FLASH CODE 12.
3. Check for short to ground in diagnostic test terminal wire between DLC terminal "B" and PCM terminal. (Scheme 272) If circuit is okay, replace PCM.

Scheme 272