Engine Controls - Basic Testing - Gasoline: Diagnosis Chevrolet Pickup K2500

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 the VACUUM DIAGRAMS article in this section 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.

A-3, NO-START DIAGNOSIS

Note. For diesel information, see TESTS W/CODES - 6.5L DIESEL and TESTS W/O CODES - 6.5L DIESEL articles in the ENGINE PERFORMANCE section.

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.

FUEL SYSTEM PRESSURE TEST

Note. Fuel pressure specification on 7.4L engines should be 26-32 psi (1.8-2.2 kg/cm 2 ), and on all others is 9-13 psi (.63-.91 kg/cm 2 ).

DIAGNOSTIC CIRCUIT CHECK

There are different/unique types of control modules, and various systems are used to control their operation depending on engine and/or vehicle type. For easier referencing, engines and models are identified or divided into system groups. See SYSTEM GROUPING CHART .

SYSTEM GROUPING CHART

Diagnostic circuit check determines following

1. Whether Malfunction Indicator Light (MIL) works.
2. Whether ECM 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 10

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 appropriate G - GASOLINE TESTS W/ CODES article in this section below.

1. G - TESTS W/CODES - 4.3L
2. G - TESTS W/CODES - 5.0L
3. G - TESTS W/CODES - 5.7L
4. G - TESTS W/CODES - 7.4L

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»(ref-19753-S41848085292001110200000). If light flashes, go to step 3).
2. Ground DLC test terminal "B". MIL should flash Code 12, followed by any codes stored in ECM memory. If light goes from bright to dim or if light remains on and does not flash Code 12, see «A-2, MIL ALWAYS ON OR WON'T FLASH CODE 12»(ref-19753-S18298989512001110200000).
3. Check for short to ground in diagnostic test terminal wire between DLC terminal "B" and ECM terminal. (Scheme 290)- (Scheme 292). If circuit is okay, replace ECM.

Scheme 290

Scheme 291

Scheme 292