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

Testing & Diagnostics 3 illustrations ~2224 words

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 - 4.3L 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 and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.

NO START DIAGNOSIS

Note. For terminal and circuit identification, see WIRING DIAGRAMS - 4.3L article.

General Inspection

  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

FUEL SYSTEM PRESSURE TEST

  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 with A/C off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-124321-S11595652702001121800000) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Bleed air out of fuel pressure gauge into container. Turn ignition off for 10 seconds. Turn ignition on with engine off. Cycle ignition to obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI fuel system. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 8).
  3. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure after fuel pump stops running. After fuel pump stops, fuel pressure should stabilize and remain constant. If pressure is within specification and holds, go to step 5). If pressure is not within specification, or is within specification but does not hold, go to next step.
  4. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-124321-S11595652702001121800000) . Disconnect fuel filter. Drain any remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-1) in place of fuel filter. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Check for leaks at shutoff valve. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for fuel pressure to build. Close valve on shutoff valve. Fuel pressure should be as specified and remain constant. If pressure is as specified and holds, go to step 12). If pressure is not as specified, or is as specified but does not hold, go to step 6).
  5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to step 27). If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 26).
  6. Check fuel feed line between shutoff valve and fuel pipes. If fuel feed line is faulty, go to step 25). If fuel feed line is okay, go to next step.
  7. Open valve on shutoff valve. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-124321-S11595652702001121800000) . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Check for leaks at fuel shutoff valve fittings. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for fuel pressure to build. Close valve on shutoff valve installed on fuel return pipe. If fuel pressure remains constant, go to step 22). If fuel pressure does not remain constant, go to step 29).
  8. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds, and then turn off. Observe fuel pressure after fuel pump stops running. If fuel pressure is present, go to step 13). If fuel pressure os not present, go to next step.
  9. Turn ignition off. Connect a fused jumper wire between battery voltage and fuel pump test terminal. Listen for operation of fuel pump. If fuel pump operates, go to next step. If fuel pump does not operate, see FUEL SYSTEM ELECTRICAL CIRCUIT under TESTS W/CODES - 4.3L.
  10. Check for plugged fuel filter, plugged fuel pump strainer or restricted fuel line. If a problem is found, go to next step. If a problem is not found, go to step 12).
  11. Repair or replace as necessary. After repairs, go to step 30).
  12. Replace fuel sending unit assembly. After replacing fuel sending unit assembly, go to step 30).
  13. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66 psi (4.6 kg/cm 2 ) on CSI fuel system or 62 psi (4.4 kg/cm 2 ) on SFI fuel system, go to next step. If fuel pressure is not greater than specified, go to step 15).
  14. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-124321-S11595652702001121800000) . Disconnect engine compartment fuel return line. Attach a flexible hose to fuel return line. Place other end of hose in container. Observe fuel pressure within 2 seconds after ignition is turned on. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI fuel system. If fuel pressure is as specified, go to step 16). If fuel pressure is not as specified, go to step 17).
  15. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi (4.2 kg/cm 2 ) on CSI fuel system or 56 psi (4.0 kg/cm 2 ) on SFI fuel system, go to step 19). If fuel pressure is not less than specified, go to step 30).
  16. Locate and repair restriction in fuel return line. After repairs, go to step 30). If fuel return line is not restricted, go to next step.
  17. Check for restriction in engine fuel return outlet pipe at point where fuel line was disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not restricted, go to step 22).
  18. Replace engine fuel pipes. After replacing engine fuel pipes, go to step 30).
  19. Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next step. If restriction is not found, go to step 21).
  20. Repair or replace in-line fuel filter and fuel line. After repairs, go to step 30).
  21. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-124321-S11595652702001121800000) . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Bleed air out of fuel pressure gauge into container. Connect a fused jumper wire between battery voltage and fuel pump test terminal. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm 2 ). Excess pressure may damage fuel pressure regulator. Slowly close valve on shutoff valve installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm 2 ) on CSI fuel system or 62 psi (4.4 kg/cm 2 ) on SFI fuel system. If fuel pressure increases as specified, go to next step. If fuel pressure does not increase as specified, go to step 23).
  22. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 30).
  23. Check for the following conditions: Low fuel pump voltage due to high resistance connections. High fuel pump voltage due to internal pump binding. Poor fuel pump ground. Partially restricted fuel pump strainer. Incorrect or faulty fuel pump. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12).
  24. Repair or replace as necessary. After repairs, go to step 30).
  25. Replace fuel feed line. After repairs, go to step 30).
  26. Start engine. Allow engine to idle until normal operating temperature is reached. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to near 66 psi (4.6 kg/cm 2 ) on CSI fuel system or 62 psi (4.4 kg/cm 2 ) on SFI fuel system. If fuel pressure increases quickly, see TESTS W/O CODES - 4.3L article. If fuel pressure does not increase quickly, go to next step.
  27. Check for the following conditions: In-line fuel filter for restriction. Fuel feed pipe for restriction. Mispositioned or damaged fuel pump strainer. Fuel pump flex pipe for leaks. Vehicle is equipped with correct fuel pump. Fuel pump electrical wiring for high resistance. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12).
  28. Repair or replace as necessary. After repairs, go to step 30).
  29. Locate and replace any leaking injector(s). After replacing leaking injector(s), go to next step. If all injectors are okay, go to FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS - 4.3L article.
  30. 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.

INJECTOR CIRCUIT DIAGNOSIS

Note. This test only applies to vehicles equipped with a VCM.

  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. Disconnect injector connector at intake manifold. Turn ignition on with engine off. Using test light connected to ground, probe injector ignition feed circuits. See WIRING DIAGRAMS - 4.3L article. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  3. Install injector test light to each injector circuit, one at a time. Crank engine. If injector test light flashes on each injector, check fuel injector(s). See FUEL SYSTEM in SYSTEM/COMPONENT TESTS - 4.3L article. If injector test light did not flash on an injector circuit, go to next step.
  4. If injector test light was on steady on any injector circuit, go to next step. If injector test light did not illuminate on any injector circuit, go to step 6).
  5. Install injector test light to affected injector. Turn ignition off. Disconnect Blue and Red VCM connectors. Turn ignition on with engine off. If injector test light turns off, go to step 11). If injector test light stays on, go to step 8).
  6. Check for open or short to battery in injector control circuit to affected injector. If circuit is open or shorted, go to next step. If circuit is okay, go to step 9).
  7. Repair circuit as necessary. After repairs, go to step 12).
  8. Repair short to ground in injector control circuit. After repairs, go to step 12).
  9. Check terminal contact at VCM connector. If terminal contact is faulty, go to next step. If terminal contact is okay, go to step 11).
  10. Repair terminal contact. After repairs, go to step 12).
  11. Replace VCM. Reprogram replacement VCM. After replacing VCM, go to next step.
  12. 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 stalls/dies, go to step 2).
  13. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any other DTC(s) is present, diagnose DTC(s). If no other DTC(s) is present, go to next step.
  14. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional undiagnosed DTC(s) are present, diagnose DTC(s). If additional DTC(s) are not present, system is okay.

Ignition Coil Test

  1. Turn ignition off. Remove engine cover. Disconnect distributor lead and wiring from ignition coil.
  2. Place DVOM on high scale. Connect DVOM as shown in step 1 of illustration. (Scheme 1) If reading is not infinite, replace ignition coil.
  3. Place DVOM on low scale. Connect DVOM as shown in step 2 of illustration. (Scheme 2) If reading is not 0.1 ohm, replace ignition coil.
  4. Place DVOM on high scale. Connect DVOM as shown in step 3 of illustration. (Scheme 3) If reading is not 5000-25,000 ohms, replace ignition coil.
  5. Reconnect distributor lead and wiring to ignition coil. Install engine cover.

Scheme 1

Scheme 1
Scheme 1

Scheme 2

Scheme 2
Scheme 2

Scheme 3

Scheme 3
Scheme 3

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