Engine Controls - Basic Diagnostic Procedures - 4.3L: Other Oldsmobile Bravada II

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see SPECIFICATIONS - 4.3L article.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (0-5 psi) gauge to check exhaust system.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction. If using a low pressure gauge, connect gauge in the following manner

1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

Definition

No start is defined as engine cranks properly, but does not start. Engine may fire a few times.

NO START - ENGINE CRANKS OKAY

Note. Before performing following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

Ignition System

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in TESTS W/CODES - 4.3L article. After performing OBD system check, go to next step.
2. Install scan tool. Using scan tool, monitor Throttle Position (TP) sensor. Ensure is throttle closed. If TP sensor value is greater than 2.5 volts, diagnose using DTC P0123. See TESTS W/CODES - 4.3L article. If TP sensor voltage is less than 2.5 volts, go to next step.
3. Using scan tool, monitor Engine Coolant Temperature (ECT) sensor. If ECT sensor value is less than -22°F (-30°C), diagnose using DTC P0118. See TESTS W/CODES - 4.3L article. If ECT sensor is greater than -22°F (-30°C), go to next step.
4. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to next step. If fuel pump does not operate as specified, go to FUEL SYSTEM ELECTRICAL CIRCUIT.
5. Turn ignition off. Disconnect injector harness connector at intake manifold. Using a test light connected to ground, probe injector feed circuit. See WIRING DIAGRAMS - 4.3L article. Turn ignition on with engine off. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Disconnect one spark plug wire. Install Spark Tester (J-26792). Crank engine. If spark is present, go to next step. If spark is not present, see «BASIC IGNITION SYSTEM CHECKS»(ref-124321-S08972475412001121800000) .
7. Reconnect spark plug wire. Turn ignition off. Connect fuel pressure gauge. Turn ignition on with engine off. Observe fuel pressure. Fuel pressure should be 55-61 psi (3.9-4.3 kg/cm 2 ). If fuel pressure is as specified, perform fuel injector balance test. See INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS - 4.3L article. If fuel pressure is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS»(ref-124321-S27016559712001121800000) .
8. Repair injector ignition feed circuit. After repairs, go to next step.
9. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and dies, go to step 2).
10. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If DTC(s) is present, diagnose DTC(s). See TESTS W/CODES - 4.3L article. If DTC(s) is not present, go to next step.
11. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) is present, diagnose DTC(s). See TESTS W/CODES - 4.3L article. If DTC(s) is not present, system is okay.

Fuel System Electrical Circuit

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in TESTS W/CODES - 4.3L article. After performing OBD system check, go to next step.
2. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to IGNITION SYSTEM. If fuel pump does not operate as specified, go to next step.
3. Connect a fused jumper wire between battery voltage and fuel pump test terminal. If fuel pump operates, go to next step. If fuel pump does not operate, go to step 12).
4. Disconnect jumper wire from fuel pump test terminal. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds, and then stops. If fuel pump operates as specified, go to step 25). If fuel pump does not operate as specified, go to next step.
5. Remove fuel pump relay. Turn ignition on with engine off. Using a test light connected to ground, probe fuel pump relay harness connector battery feed circuit. See WIRING DIAGRAMS - 4.3L article. If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
6. Connect test light between ground and fuel pump relay harness connector battery feed circuit. See WIRING DIAGRAMS - 4.3L article. If test light illuminates, go to next step. If test light does not illuminate, go to step 15).
7. Connect test light between ground and fuel pump relay control terminal. Turn ignition off for 10 seconds. Turn ignition on. Test light should illuminate for 2 seconds, and then turn off. If test light illuminates as specified, go to next step. If test light does not illuminate as specified, go to step 16).
8. Check for faulty connection at fuel pump relay control connector terminal. Repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
9. Replace fuel pump relay. After repairs, go to next step.
10. Start and warm engine to normal operating temperature. Ensure oil pressure is within normal range. Disconnect fuel pump relay. If engine continues to run, go to next step. If engine stalls/dies, go to step 17).
11. Reinstall fuel pump relay. Turn ignition off. Using a test light connected to ground, probe fuel pump test connector. If test light illuminates, go to step 18). If test light does not illuminate, go to step 25).
12. Disconnect chassis fuel pump harness connector at fuel tank. Using a fused jumper wire connected to battery voltage, jumper fuel pump test terminal. Using a test light connected to ground, probe fuel pump feed circuit at fuel tank. See WIRING DIAGRAMS - 4.3L article. If test light illuminates, go to next step. If test light does not illuminate, go to step 20).
13. Using test light connected to fuel pump ground circuit (tank side), probe fuel pump feed circuit (engine side). See WIRING DIAGRAMS - 4.3L article. If test light illuminates, go to step 19). If test light does not illuminate, go to step 21).
14. Repair open in battery feed circuit to fuel pump relay harness connector terminal. After repairs, go to step 25).
15. Repair open in fuel pump relay ground circuit. After repairs, go to step 25).
16. Check for faulty connection at VCM connector fuel pump relay control circuit. Check for open or short to ground in harness between fuel pump relay connector terminal, fuel pump relay control connector terminal and fuel pump relay control circuit. Repair as necessary. After repairs, go to step 22). If circuits are okay, go to step 24).
17. Check for faulty connection at fuel pump oil pressure switch harness connector terminals. Repair as necessary. After repairs, go to step 22). If connection is okay, go to next step.
18. Replace fuel pump oil pressure switch. After repairs, go to step 25).
19. Replace fuel pump. After repairs, go to step 25).
20. Repair open between fuel pump test terminal and fuel pump feed circuit at fuel pump harness connector. After repairs, go to step 25).
21. Repair open in fuel pump harness ground circuit. After repairs, go to step 25).
22. Repair affected circuit as necessary. After repairs, go to step 25).
23. Repair connections as necessary. After repairs, go to step 25).
24. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
25. Using scan tool, clear DTC(s). Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls/dies, go to step 2).
26. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTC(s) is present, diagnose DTC(s). See TESTS W/CODES - 4.3L article. If DTC(s) is not present, go to next step.
27. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) is present, diagnose DTC(s). See TESTS W/CODES - 4.3L article. If DTC(s) is not present, system is okay.

FUEL SYSTEM PRESSURE RELIEF

Note. For fuel pump circuit testing, FUEL SYSTEM ELECTRICAL CIRCUIT in NO START DIAGNOSIS .

Fuel system is under pressure. Pressure must be relieved prior to servicing fuel system. Fuel pressure may be relieved by using the following method.

1. Disconnect negative battery cable. Loosen fuel filler cap. Install Fuel Pressure Gauge (J-34730-1A) to fuel pressure connection. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to relieve fuel pressure.

Spark

1. If factory tachometer is connected to coil tachometer terminal, disconnect tachometer before performing tests. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.
2. Using Spark Tester (J-26792), check for spark at each spark plug wire. Leave other wires connected while checking for spark. Check spark plug wire resistance on suspect wires. Resistance should be about 30,000 ohms.

Ignition Coil Power Source

Turn ignition on. Check ignition positive voltage circuit of ignition control module for battery voltage. See WIRING DIAGRAMS - 4.3L article. If battery voltage is not present, check ignition or ECM 1 fuse. If fuse is not blown, check for open between fuse and ignition control module.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specifications. For specifications, see SPECIFICATIONS - 4.3L article. For adjustment procedures, see ADJUSTMENTS - 4.3L article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, no trouble codes (or only intermittent ones) were found while performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK and driveability problems exist, proceed to TESTS W/O CODES - 4.3L article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.