Engine Controls - Basic Engine Testing 3.8l Buick Riviera VIII

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions during which the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed.

A & C CHART REFERENCE TABLE

Note. The following table provides the location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into the appropriate location in the new Engine Performance workflow. To familiarize yourself with the Engine Performance workflow, see HOW TO USE THE ENGINE PERFORMANCE SECTION in this section.

GENERAL MOTORS A & C CHART REFERENCE

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

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. See VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

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 article.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. The exhaust system can be checked with a vacuum gauge or a low pressure (0-5 psi) pressure gauge.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way 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 one of the following manners

1. Check At AIR Pipe Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install pressure gauge to hose and nipple via Propane Enrichment Device(J-26911). Nipple should be inserted into exhaust manifold AIR pipe.
2. 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.

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ). Exhaust system is restricted if specification is exceeded.
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.

PCM REPLACEMENT CHECK

Many test procedures and test charts in ENGINE PERFORMANCE lead to conclusion that PCM is faulty. Before replacing PCM, check driven circuits and PCM Quad-Drivers (QDR) using following procedures and accompanying flow chart. (Scheme 1)

1. Using a DVOM, backprobe PCM drive circuit in question and measure pin voltage with ignition on. If system voltage is present, go to next step. If system voltage is not present, turn ignition off. Disconnect PCM connector. Measure voltage on connector terminal for suspect circuit. If low voltage is measured, check circuit for an open or short to ground. Repair as necessary. If system voltage is measured, PCM is defective.
2. With DVOM still backprobing PCM at suspect circuit, ground DLC "test" terminal. Monitor voltage drop on circuit for at least 2 minutes. Voltage drop should not be greater than.5 volt. Some circuits may have low voltage until DLC "test" terminal is grounded. A "switching" operation should occur. Some Torque Converter Clutch (TCC) systems have pressure switches in series with TCC solenoid. On these applications, complete this circuit by disconnecting transaxle connector and using a test light in series between transaxle connector terminals.
3. If voltage drops and then floats back up, this occurs when QDR circuit is going into current limiting. Check circuit current flow (.75 amp maximum, except as noted in QDR check chart). (Scheme 1)

Note. For PCM-equipped vehicles, transaxle functions can only be energized through use of TECH 1 scan tool. Shift solenoids on these models will not energize when DLC is grounded.

Scheme 1

NO START DIAGNOSIS (A-3)

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 trouble code in PCM memory.

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.

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.

Ignition System (VIN K & 1)

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Turn ignition on. Using scan tool, select FAILED SINCE CODE CLEAR test. If Diagnostic Trouble Code (DTC) P0123, P0506, P0601, P0602 or P1629 is present, diagnose applicable DTC. See TESTS W/CODES article. If DTC is not present, go to next step.
3. Using scan tool, observe Engine Speed display while cranking engine. If RPM is indicated, go to next step. If RPM is not indicated, go to step 22).
4. Turn ignition off. Disconnect injector harness connector. Install Injector Test Light (J-34730-2) to injector harness connector. (Scheme 2) Turn ignition on. If injector test light illuminates, go to step 17). If injector test light does not illuminate, go to next step.
5. Crank engine and monitor injector test lights. If all injector test lights flashes, go to next step. If any of injector test light does not flash, go to step 18).
6. Turn ignition off. Install fuel pressure gauge to fuel injector test fitting. Turn ignition on and observe fuel pressure. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ) and holding. If fuel pressure is as specified, go to step 8). If fuel pressure is not as specified, go to next step.
7. If fuel pressure is indicated, but is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS (A-7)»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__basic-fuel-system-checks-a-7). If fuel pressure is not present, see FUEL SYSTEM test.
8. Check for fuel contamination. If fuel is contaminated, clean fuel system and then perform OBD system check. If fuel is not contaminated, go to next step.
9. Install Spark Tester (ST-125) to an ignition wire. Connect one end of ignition wire to one coil tower of cylinders No. 2, 4 and 6 (one at a time). Clip spark tester to coil tower of each companion cylinder. Crank engine. Spark should be present. If spark is present, go to next step. If spark was not present, go to step 11).
10. Remove and inspect spark plugs from all cylinders. If spark plugs are okay, go to step 37). If spark plugs shows excessive fouling, check engine for mechanical problems.
11. If spark is present at any ignition wires, go to next step. If spark is not present at any of ignition wires, go to step 40).
12. Remove and inspect ignition coil to affected cylinder for cracks or carbon tracking. Replace faulty ignition coil. After repairs, perform OBD system check. If coil(s) are okay, go to next step.
13. Check secondary ignition resistance. Resistance should be 5000-8000 ohms. If resistance is as specified, go to next step. If resistance is not as specified, perform OBD system check.
14. Remove and inspect ignition wire to affected cylinder for cracks or carbon tracking. Replace faulty ignition wire(s). After repairs, perform OBD system check. If wire(s) were okay, go to next step.
15. Check ignition wire resistance. Resistance should be about 30,000 ohms. If resistance is as specified, perform OBD system check. If resistance is not as specified, go to next step.
16. Connect test light across ignition module primary circuit (between ignition control terminals) for coils associated with cylinder that did not have a spark. (Scheme 2) Crank engine. If test light flashes, go to step 39). If test light does not flash, go to step 40).
17. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Observe injector test lights. If injector test lights illuminate, go to step 34). If injector test lights does not illuminate, go to step 38).
18. If any of injector test light flashed, go to next step. If injector test light did not flash, go to step 22).
19. Check fuse to affected injector ignition feed circuit. If a fuse is faulty, repair short to ground in fuel injector ignition feed circuit. After repairs, perform OBD system check. If fuse is okay, go to next step.
20. Disconnect injector test light that did not flash when engine was being cranked. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit at each injector connector. If test light illuminates on all injector connectors, go to next step. If test light does not illuminate on all injector connectors, go to step 35).
21. Turn ignition off. Disconnect PCM harness connector. Check affected injector circuit driver for an open in circuit. (Scheme 2) Repair open circuit. After repairs, perform OBD system check. If circuit is okay, go to step 38).
22. Check fuse to ignition control module feed circuit. (Scheme 2) If fuse is faulty, locate and repair short to ignition control module feed circuit or short to voltage in IC circuit. After repairs, perform OBD system check. If fuse is okay, go to step 36).
23. Turn ignition off. Disconnect ignition control module harness connector. Turn ignition on. Using a test light connected to ground, probe ignition control module ignition feed circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 36).
24. Install an injector test light to any of injector harness connector. Turn ignition on. Using a test light connected to battery voltage, repeatedly touch test light to 3X reference circuit at ignition module harness connector. (Scheme 2) If injector test light flashes, go to next step. If injector test does not flash, go to step 33).
25. Turn ignition off. Using a fused jumper wire, jumper CKP sensor ignition feed circuit at ignition control module harness connector to battery voltage. Connect a second jumper between ground and CKP sensor ground circuit at ignition control module harness connector. Connect DVOM between CKP sensor signal circuit at ignition control module harness connector and battery voltage. Crank engine and observe DVOM voltage reading. DVOM should read 1-3 volts. If voltage reading is as specified, go to step 29). If voltage reading is not as specified, go to next step.
26. If voltage reading is greater than 3 volts, go to next step. If voltage reading is less than 3 volts, go to step 28).
27. Disconnect CKP sensor harness connector. Using a test light connected to battery voltage, probe sensor signal circuit. (Scheme 2) If test light illuminates, locate and repair short to ground in sensor sync circuit. After repairs, perform OBD system check. If test light does not illuminate, go to step 41).
28. Check CKP sensor for sync signal circuit that is open or shorted to voltage, open ground circuit or open or shorted feed circuit. (Scheme 2) Repair as necessary. After repairs, perform OBD system check. If circuits were okay, go to step 41).
29. Using DVOM, check voltage between CKP 18X signal circuit at ignition control module connector and battery voltage. Crank engine and observe DVOM voltage reading. Voltage reading should be 5-7 volts. If voltage reading is as specified, go to step 40). If voltage reading is not as specified, go to next step.
30. If voltage reading is greater than 7 volts, go to next step. If voltage reading is less than 5 volts, go to step 32).
31. Disconnect CKP 18X sensor harness connector. Using a test light connected to battery positive, probe sensor signal circuit. (Scheme 2) If test light illuminates, locate and repair short to ground in signal circuit. After repairs, perform OBD system check. If circuit is okay, go to step 41).
32. Check CKP 18X signal circuit for open or short to voltage. Repair as necessary. After repairs, perform OBD system check. If circuit is okay, go to step 41).
33. Turn ignition off. Disconnect PCM harness connector. Check 3X reference circuit for open or short. Repair as necessary. After repairs, perform OBD system check. If circuit is okay, go to step 38).
34. Locate and repair short to ground in injector driver circuit(s) to affected injector (test light stayed on). (Scheme 2) After repairs, perform OBD system check.
35. Locate and repair open in fuel injector ignition feed circuit. (Scheme 2) After repairs, perform OBD system check.
36. Locate and repair open in ignition control module ignition feed circuit. (Scheme 2) After repairs, perform OBD system check.
37. Repair engine mechanical problem. Check for bent push rods, faulty or incorrect camshaft, leaking or sticky valves or rings, excessive valve deposits, loose or worn rocker arms, weak valve springs, incorrect valve timing or a leaking head gasket. Repair as necessary. After repairs, perform OBD system check.
38. Replace PCM. Perform PCM relearn procedures and then perform OBD system check.
39. Replace affected ignition coil(s) that did not produce a spark. After repairs, perform OBD system check.
40. Replace ignition control module. After repairs, perform OBD system check.
41. Replace CKP sensor. After repairs, perform OBD system check.

Fuel System (VIN K)

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. Turn ignition off. Install fuel pressure gauge to fuel pressure test port. Disconnect fuel pump relay. Using a fused jumper wire, jumper fuel pump feed circuit (Red wire) at fuel pump relay connector to battery voltage. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 10).
3. Disconnect jumper from fuel pump relay connector. Connect test light between fuel pump relay connector terminal for ignition feed circuit (Orange wire) and ground. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
4. Turn ignition off. Connect test light between fuel pump relay terminal for fuel pump relay driver circuit (Dark Green/White wire) and ground. Turn ignition on. Test light should illuminate for about 2 seconds. If test light illuminates, go to step 8). If test light does not illuminate, go to next step.
5. Turn ignition off. Disconnect PCM. Using a test light connected to battery voltage, probe fuel pump driver circuit at PCM connector (Dark Green/White wire). If test light illuminates, go to step 15). If test light does not illuminate, go to next step.
6. Check continuity of fuel pump relay driver circuit between PCM and fuel pump relay. If circuit is open, repair as necessary and then go to step 21). If circuit is okay, go to next step.
7. Check fuel pump relay driver circuit for poor terminal connection at PCM. If connection is okay, go to step 18). If connection is faulty, repair as necessary and then go to step 21).
8. Check fuel pump relay terminal connection. If connection is okay, go to step 18). If connection is faulty, repair as necessary and then go to step 21).
9. Using test light connected to ground, probe ignition feed circuit at fuel pump relay connector (Orange wire). If test light illuminates, go to step 17). If test light does not illuminate, go to step 16).
10. Remove fuel filler cap and listen for fuel pump operation. If fuel pump is running, check fuel system. See BASIC FUEL SYSTEM CHECKS (A-7). If fuel pump is not running, go to next step.
11. Using a fused jumper wire, connect battery voltage to fuel pump feed circuit (Gray wire). Raise and support vehicle. Disconnect fuel sending unit harness connector at fuel tank. Using a test light, check voltage between fuel sending unit harness connector terminals. If test light illuminates, go to step 19). If test light does not illuminate, go to next step.
12. Using test light connected to ground, probe fuel pump feed circuit (Gray wire) at harness connector. If test light does not illuminate, go to next step. If test light illuminates, go to step 14).
13. Locate and repair open in fuel pump feed circuit (Gray wire). After repairs, perform OBD system check.
14. Locate and repair open in fuel pump ground circuit (Black wire). After repairs, perform OBD system check.
15. Locate and repair short to ground in fuel pump relay driver circuit (Dark Green/White wire). After repairs, perform OBD system check.
16. Locate and repair open in ignition feed to fuel pump relay (Orange wire). After repairs, perform OBD system check.
17. Locate and repair open in ground circuit to fuel pump relay (Black wire). After repairs, perform OBD system check.
18. Replace fuel pump relay and then perform OBD system check.
19. Replace fuel pump and then perform OBD system check.
20. Replace PCM. Perform PCM relearn procedures and then perform OBD system check.
21. Turn ignition on. Using scan tool, select FP RELAY OUTPUT CONTROL function. Observe fuel pressure gauge while activating fuel pump with scan tool. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ). If fuel pressure is not as specified, repeat step 2).

Fuel System (VIN 1)

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. If Diagnostic Trouble Code (DTC) P1643 is present, diagnose DTC. See TESTS W/CODES article. If DTC is not present, go to next step.
3. Turn ignition off. Install fuel pressure gauge to fuel pressure test port. Using a scan tool, select FP RELAY OUTPUT CONTROL function. Observe fuel pressure gauge while activating fuel pump with scan tool. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 5).
4. Start engine. Using scan tool, switch fuel pump speed between normal and high. Fuel pressure should slightly increase when high fuel pump speed is selected. If fuel pressure increases, no trouble is found. If fuel pressure does not change, go to step 31).
5. Turn ignition off. Disconnect fuel pump control module. Using a fused jumper wire, jumper fuel pump feed control module harness connector terminal No. 6 (Gray wire) to battery voltage. Connect a second jumper wire between fuel pump control module harness connector terminal No. 5 (Pink wire) and ground. Observe fuel pressure gauge. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 26).
6. Disconnect jumpers from fuel pump control module. Connect test light between fuel pump control module connector terminal No. 8 (Light Green) and terminals No. 4 (Black wire). Turn ignition on. Using scan tool, activate fuel pump. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
7. Using test light connected to battery voltage, probe fuel pump control module terminal No. 4 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 25).
8. Turn ignition off. Disconnect PCM. Using a test light connected to battery voltage, probe fuel pump driver circuit at PCM connector (Brown wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
9. Locate and repair short to ground in fuel pump driver circuit (Brown wire). After repairs, go to step 39).
10. Turn ignition off. Reconnect PCM harness connector. Turn ignition on. Connect DVOM between fuel pump module connector terminals No. 4 (Black wire) and No. 7 (Brown wire). Using scan tool, command fuel pump on and off. DVOM should read greater than 8 volts while fuel pump relay is commanded on. If voltage is as specified, go to next step. If voltage is not as specified, go to step 38).
11. Turn ignition off. Reconnect fuel pump control module connector. Turn ignition on. Connect test light between fuel pump control module terminals No. 4 and No. 7. Using scan tool, command fuel pump relay on and off. Test light should illuminate when fuel pump is commanded on. If test light illuminates, go to next step. If test light does not illuminate, go to step 34).
12. Check for poor terminal connection at fuel pump control module. Repair as necessary. After repairs, go to step 39). If terminals were okay, check PCM harness and connectors for improper mating, check for rubbed through wire insulation or a wire broken inside insulation.
13. Turn ignition off. Remove fuel pump relay. Turn ignition on. Using a test light connected to ground, probe fuel pump relay harness connector terminal No. 87 (Light Green). If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
14. Connect test light between fuel pump relay harness connector terminals No. 86 (Black/White wire) and No. 87 (Light Green wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 20).
15. Connect test light between fuel pump relay harness connector terminal No. 87 (Light Green wire) and fuel pump control module harness connector terminal No. 86 (Black/White wire). Using scan tool, activate fuel pump. If test light illuminates when fuel pump is activated, go to next step. If test light does not illuminate, go to step 21).
16. Connect jumper wire between fuel pump relay harness connector terminal No. 87 and fuel pump control module harness connector terminal No. 30 (Red wire). Using a test light connected to ground, probe fuel pump control module harness connector terminal No. 5 (Pink wire). If test light does not illuminate, go to step 24). If test light illuminates, go to next step.
17. Check for faulty harness terminal connection at relay. Repair as necessary. After repairs, go to step 39). If terminals are okay, go to next step.
18. Replace fuel pump relay. After repairs, go to step 39).
19. Locate and repair open in fuel pump relay feed circuit. After repairs, go to step 39).
20. Locate and repair open in fuel pump relay ground circuit. After repairs, go to step 39)
21. Turn ignition off. Disconnect PCM. Using a test light connected to battery voltage, probe fuel pump relay driver circuit at PCM connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 23).
22. Locate and repair short to ground in fuel pump relay driver circuit. After repairs, go to step 39).
23. Check fuel pump relay driver circuit for poor connection or open circuit between fuel pump relay and PCM. Repair as necessary. After repairs, go to step 39). If connection and circuit are okay, go to next step.
24. Locate and repair open in fuel pump control module feed circuit. After repairs, go to step 39).
25. Locate and repair open in fuel pump control module ground circuit. After repairs, go to step 39).
26. Remove fuel filler cap and listen for fuel pump operation. If fuel pump is running, check fuel system. See «BASIC FUEL SYSTEM CHECKS (A-7)»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__basic-fuel-system-checks-a-7) . If fuel pump is not running, go to next step.
27. Using a fused jumper wire, connect battery voltage to fuel pump feed circuit (Gray wire). Raise and support vehicle. Disconnect fuel sending unit harness connector at fuel tank. Using a test light, check fuel sending unit circuit between harness connector terminals. If test light illuminates, go to step 36). If test light does not illuminate, go to next step.
28. Using test light connected to ground, probe fuel pump feed circuit at harness connector. If test light does not illuminate, go to next step. If test light illuminates, go to step 30).
29. Locate and repair open in fuel pump feed circuit (Gray wire). After repairs, go to step 39).
30. Locate and repair open in fuel pump ground circuit (Pink wire). After repairs, go to step 39).
31. Connect test light between fuel pump control module terminals No. 7 and No. 8. Start and idle engine. Using scan tool, select FP SPEED OUTPUT CONTROL. Observe test light while switching scan tool between normal and high. Test light should illuminate when normal is selected and then turn off when high is selected. If test light illuminates as indicated, go to next step. If test light does not illuminate as indicated, go to step 33).
32. Connect DVOM between fuel pump control module terminals No. 5 and No. 6. With engine at idle, select FP SPEED OUTPUT CONTROL with scan tool. Observe DVOM voltage reading while switching scan tool between normal and high speed. On normal speed, DVOM should read about 7.0 volts. On high speed, DVOM should read battery voltage. If voltage readings are as specified, go to step 36). If voltage readings are not as specified, go to step 34).
33. Check fuel pump driver circuit for poor terminal connection or an open or short to voltage between fuel pump control module and PCM. Repair terminal or circuit as necessary. After repairs, go to step 39). If circuit or terminal is okay, go to step 38).
34. Check terminal connection at fuel pump control module. If terminals are okay, go to next step. If terminals are faulty, repair or replace as necessary and then go to step 39).
35. Replace fuel pump control module and then go to step 39).
36. Check terminal connection at fuel pump. If terminals are okay, go to next step. If terminals are faulty, repair or replace as necessary and then go to 39).
37. Replace fuel pump and then go to step 39).
38. Replace PCM. Ensure PCM relearn procedure is performed. After repairs, go to next step.
39. Turn ignition on. Using scan tool, select FP RELAY OUTPUT CONTROL function. Turn fuel pump on with scan tool. Fuel pressure should be 48-55 psi (3.4-3.9 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 5).
40. Start and idle engine. Using scan tool, select FP RELAT CONTROL OUTPUT function, switch fuel pump speed to normal and high speed. Fuel pressure should slightly increase when high fuel pump speed selected. If pressure does not change, go to step 31).

Scheme 2

BASIC FUEL SYSTEM CHECKS (A-7)

Fuel Pressure Relief

Fuel system is under pressure. Pressure must be relieved prior to servicing fuel system. Disconnect negative battery terminal. Loosen fuel filler cap. Install Fuel Pressure Gauge J-34730-1) on fuel pressure connector of fuel rail. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Install gauge bleed hose in container. Open bleed valve to bleed fuel pressure.

Fuel Pressure Check

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF. Connect Fuel Pressure Gauge (J-34730-1) to fuel pressure fitting on fuel rail. With gauge installed, turn ignition on. With ignition on and engine off, fuel pressure should read within specification. See «FUEL PRESSURE»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l) table. If no fuel pressure is present, go to step 5).
2. Start engine. Pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). Turn ignition off. Pressure should hold. If pressure does not hold, check for leaking injectors or fittings. If injectors or fittings are not leaking, replace pressure regulator.
3. If fuel pressure is less than specification, check for restricted fuel line or fuel filter. Repair as necessary. If no restriction is evident, apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS article.
4. Gradually pinch off fuel return line between gauge and fuel tank. If fuel pressure increases to within specification, replace fuel pressure regulator. If fuel pressure does not increase with line pinched, check for faulty in-tank fuel pump or partially blocked fuel strainer.
5. Apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS article. Observe fuel pressure reading. If fuel pressure is still not present, check wiring between test connector and fuel pump. If wiring is okay, replace fuel pump.
6. If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. See SYSTEM/COMPONENT TESTS article.

FUEL PRESSURE (EXCEPT SATURN)

Fuel Pump Relay

See MOTORS, RELAYS & SOLENOIDS in SYSTEM/COMPONENT TESTS article.

Fuel Pump Relay By-Pass Procedure

See FUEL DELIVERY in SYSTEM/COMPONENT TESTS article.

See FUEL DELIVERY in SYSTEM/COMPONENT TESTS article.

See FUEL DELIVERY in SYSTEM/COMPONENT TESTS article.

SPARK

Disconnect tachometer wire (if equipped). A shorted tachometer will prevent vehicle from starting. Disconnect cam sensor, and attempt to start engine. If engine starts, see appropriate cam sensor trouble code in TESTS W/CODES article. Check for adequate spark using Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.

IGNITION COIL POWER SOURCE

Turn ignition on. Check for battery voltage on Pink/Black wire to ignition module. If battery voltage is not present, check for blown ignition fuse. If fuse is not blown, check for open between fuse and ignition module.

IGNITION COIL RESISTANCE

Disconnect ignition coil leads. Use an ohmmeter to check ignition coil resistance. Secondary resistance should be 5000-8000 ohms. Replace ignition coil if not within specification.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article.

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) works.
2. If PCM is operating and can recognize a fault.
3. If any codes 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 TESTS W/O CODES article and SCAN TESTER USAGE in TESTS W/CODES article.

1. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to «A-1, MIL INOPERATIVE»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__a-1-mil-inoperative) .
2. 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 A-2/A-4, DLC DIAGNOSIS OR NO SCAN TOOL DATA.
3. 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 (A-3)»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__no-start-diagnosis-a-3) .
4. Using scan tool, observe DTC statuses; MIL REQUEST, FAIL THIS IGN, LAST TST FAIL and HISTORY. If any of these DTC status are present, refer to affected DTC to diagnose problem. If DTC(s) are not present, check related circuit or component(s). See SYSTEM/COMPONENT TESTS article.

Scheme 3

A-1, MIL INOPERATIVE

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Turn ignition on with engine off. If Malfunction Indicator Light (MIL) illuminates, go to step 4). If MIL does not illuminate, go to next step.
3. Start engine. If engine starts, go to step 5). If engine does not start, go to step 6).
4. Install Tech 1 scan tool. Turn ignition on. Using scan tool, command MIL to turn on and off. If MIL turns on and off as commanded, go to step 24). If MIL does not turn on and off as commanded, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a test light connected to ground, probe MIL driver circuit (Brown/White wire). (Scheme 3) If MIL illuminates, go to step 7). If MIL does not illuminate, go to step 8).
6. Inspect ignition and battery fuses. If fuses are okay, go to step 9). If fuses are faulty, go to step 10).
7. Using a test light connected to ground, probe PCM harness connector ignition feed terminal No. 3 (Pink wire). (Scheme 3) If test light illuminates, go to step 11). If test light does not illuminate, go to step 12).
8. If test light illuminated, go to step 13). If test light did not illuminate, go to step 19).
9. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to ground, probe PCM harness connector ignition feed circuit No. 2 (Pink wire). (Scheme 3) If test light illuminates, go to test 18). If test light does not illuminate, go to step 19).
10. Check for short to ground in fuse circuit that was open. (Scheme 3) Repair as necessary and replace fuse. After repairs, go to step 22).
11. Check for faulty PCM connections. If connections are okay, replace PCM and then perform OBD system check. After repairs, go to step 22).
12. Repair open in ignition feed circuit No. 3 (Pink). (Scheme 3) After repairs, go to step 22).
13. Repair short to voltage in MIL control circuit (Brown/White wire). (Scheme 3) After repairs, go to step 22).
14. Check for open in MIL control circuit. Repair as necessary. After repairs, go to step 22). If circuit is okay, go to next step.
15. Check for open in ignition feed circuit or fuse to MIL. (Scheme 3) Repair as necessary. After repairs, go to step 22). If circuit or fuse is okay, go to next step.
16. Check for an open MIL bulb. If light bulb is faulty, go to step 22). If light bulb is okay, go to next step.
17. Replace instrument cluster assembly. After replacing instrument cluster, go to step 22).
18. Using test light connected to ground, probe battery feed circuit (Orange wire). (Scheme 3) If test light illuminates, go to step 20). If test light does not illuminate, go to step 21).
19. Repair open in ignition feed circuit No. 2 (Pink wire). (Scheme 3) After repairs, go to step 22).
20. Check for faulty PCM ground connection at engine block. After repairs, go to step 22). If connections were okay, go to step 11).
21. Repair open in battery feed circuit (Orange wire). (Scheme 3) After repairs, go to next step.
22. Start and warm engine to normal operating temperature. Check if any DTCs are set. Diagnose any DTC present. See TESTS W/CODES article.

A-2/A-4, DLC DIAGNOSIS OR NO SCAN TOOL DATA

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-basic-engine-testing-38l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. Turn ignition on with engine off. Connect a test light between DLC terminal No. 16 (Orange wire) and DLC terminal No. 4 (Black/White or Black wire). If test light illuminates, go to step 4). If test light does not illuminate, go to next step.
3. Connect test light to ground. Using test light, probe DLC terminal No. 16 (Orange wire). If test light illuminates, go to next step 9). If test light does not illuminate, go to step 10).
4. Turn ignition on with engine off. Using DVOM, check voltage between ground and DLC terminal No. 2 (Purple wire). DVOM should read zero volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 7).
5. Turn ignition off. Disconnect PCM harness connector. Turn ignition on with engine off. Connect DVOM between battery voltage and DLC terminal No. 2 (Purple wire). DVOM should read zero volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 8).
6. Check for open in circuit (Purple wire) between DLC and PCM connector. If circuit is open, repair as necessary. After repairs, perform OBD system check. If circuit is okay, go to step 11).
7. Check for short to voltage in circuit (Purple wire) between DLC and PCM connector. If circuit is shorted, repair as necessary. After repairs, perform OBD system check. If circuit is okay, go to step 11).
8. Check for short to ground in circuit (Purple wire) between DLC and PCM connector. If circuit is shorted, repair as necessary. After repairs, perform OBD system check.
9. Locate and repair open in DLC ground circuit (Black wire). After repairs, perform OBD system check.
10. Locate and repair open or short to ground in DLC terminal No. 16 (Orange wire). After repairs, perform OBD system check.
11. Replace PCM. Perform PCM relearn procedures and then perform OBD system check.

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 SYSTEM CHECK and driveability problems exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.

See also:
• SPECIFICATIONS
• ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
• NO START - ENGINE CRANKS OKAY
• BASIC FUEL SYSTEM CHECKS (A-7)
• PCM REPLACEMENT CHECK
• FUEL PRESSURE
• A-1, MIL INOPERATIVE
• NO START DIAGNOSIS (A-3)