Engine Control System - Basic Engine Testing - 5.7L: Diagnosis Pontiac Firebird IV

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 not pinched or cut. If necessary, see VACUUM DIAGRAMS 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. Some vehicles are equipped with anti-theft systems (VATS or PASS-Key(R)) which will not allow vehicle to be started if improper starting procedures or improperly coded ignition keys are used. Both fuel injection and cranking systems will be disabled. Loss of fuel enable signal from anti-theft decoder module should set a diagnostic trouble code in PCM memory.

Note. For terminal and circuit ID, see the WIRING DIAGRAMS 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.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

Note. Tech 1 scan tool is required to perform OBD system check.

The OBD System Check determines

1. If Malfunction Indicator Light (MIL) operates.
2. If PCM is operating and can recognize a fault.
3. If any DTCs are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see the TESTS W/O CODES article and SCAN TOOL USAGE in the TESTS W/CODES article.

1. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(ref-20656-S33160055782001010200000) .
2. Attempt to start engine. If engine start and runs, go to next step. If engine does not start or starts and dies, go to «NO START DIAGNOSIS»(ref-20656-S26466514712001010200000) .
3. Using scan tool, select DTC, DTC INFO and LAST TST FAIL function. If any DTC is stored, go to step 5). If no DTCs are stored, go to next step.
4. Using scan tool, select DTC, DTC INFO and HISTORY function. If no DTCs are stored, go to step 6). If any DTC is stored, go to next step.
5. Using scan tool, save freeze frame and fail record information using CAPTURE INFO feature. If any DTC is indicated as last test failed, diagnose DTC. See the TESTS W/CODES article.
6. Compare scan tool engine data with actual control system data values. If value is within limits, see the TESTS W/O CODES article. If value is not within limits, go to the SYSTEM/COMPONENT TESTS article.

DLC DIAGNOSIS OR NO SCAN TOOL DATA

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) . After performing OBD system check, go to next step.
2. Turn ignition on with engine off. Install scan tool. If scan tool powers up, go to next step. If scan tool does not power up, go to step 10).
3. If engine starts and continues to run, go to step 15). If engine does not start, or starts and then dies, go to next step.
4. Turn ignition off. Disconnect PCM connector. Using a test light connected to ground, probe PCM battery feed circuit and ignition feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Using DVOM, measure resistance between chassis ground and PCM ground circuits. See the WIRING DIAGRAMS article. DVOM should read 5 ohms or less for each circuit. If resistance is as specified, go to next step. If resistance is not as specified, go to step 8).
6. Check for poor PCM connections. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) . If connections are okay, go to step 9).
7. Repair circuit that did not illuminate test light. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
8. Repair faulty PCM ground circuits. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
9. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
10. Disconnect scan tool. Using a test light connected to ground, probe DLC battery feed circuit. See the WIRING DIAGRAMS article. If test light does not illuminate, go to step 12). If test light illuminates, go to next step.
11. Using DVOM, measure resistance between chassis ground and DLC ground circuits. See the WIRING DIAGRAMS article. DVOM should read 5 ohms or less for each circuit. If resistance is as specified, go to step 14). If resistance is not as specified, go to step 13).
12. Repair DLC battery feed circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
13. Repair DLC ground circuits. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
14. Replace faulty scan tool. After scan tool replacement, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
15. Using DVOM, measure resistance between chassis ground and DLC ground circuits. See the WIRING DIAGRAMS article. DVOM should read 5 ohms or less for each circuit. If resistance is as specified, go to next step. If resistance is not as specified, go to step 17).
16. Check for open, short to voltage or short to ground in class 2 serial data circuit. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) . If circuit is okay, go to step 18).
17. Repair DLC ground circuits. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
18. Install scan tool on another vehicle and check for proper operation. If scan tool operates properly, go to next step. If scan tool does not operate properly, go to step 20).
19. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .
20. Replace faulty scan tool. After scan tool replacement, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20656-S10587673782001010200000) .