Engine Controls - Basic Engine Testing 4.6l Cadillac Eldorado X

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 in this article.

Note. Unless otherwise instructed in test procedures, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.

The following table provides the location of commonly used diagnostic information.

GENERAL MOTORS REFERENCE

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.

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 the SPECIFICATIONS 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 one of the following manners

1. Check At AIR Check Valve Remove AIR check valve. Install backpressure tester in place of AIR check valve.
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 before installation.

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.

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. Check battery, engine cranking speed and fuel supply before performing the following tests.

General Inspection

1. Ensure proper starting procedure is being used.
2. 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.
3. In very cold temperatures, ensure oil is of proper viscosity and not contaminated with gasoline.

Ignition System

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. If Diagnostic Trouble Code (DTC) P0231, P0232, P0322, P0601, P0602, P1376, P1631, P1632 or P1634 is present, diagnose DTC(s) first. See the TESTS W/CODES article. If DTC(s) are not present, go to next step.
3. Check all PCM power and ground connections and circuits. Repair as necessary. After repairs, go to step 6). If connections and circuits are okay, go to next step.
4. Check ignition system. Repair as necessary. After repairs, go to step 6). If ignition system is okay, go to next step.
5. Check fuel system. Go to FUEL SYSTEM or «BASIC FUEL SYSTEM CHECKS»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__basic-fuel-system-checks) . Repair as necessary. After repairs, go to next step. If fuel system is okay, go to step 7).
6. Start engine. If engine starts, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . If engine still does not start, go to next step.
7. Check for engine mechanical condition causing a no-start condition. Check timing chain and valve timing. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . Fuel System (Fuel Metering System)

Fuel System

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. If referred to this test from a DTC test procedure, go to step 4). If not referred to this test from a DTC test procedure, go to next step.
3. Install scan tool. Turn ignition on. Check for Diagnostic Trouble Codes (DTCs). If DTC is present, diagnose DTC. See the TESTS W/CODES article. If DTC is not present, go to next step.
4. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts but dies, go to FUEL SYSTEM PRESSURE TEST under «BASIC FUEL SYSTEM CHECKS»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__basic-fuel-system-checks) .
5. If complaint is a fuel leak or odor, go to step 10). If complaint is not a fuel leak or odor, go to next step.
6. If complaint is a fuel odor, go to step 11). If complaint is not a fuel leak or odor, go to next step.
7. If complaint is a malfunctioning fuel gauge, diagnose faulty fuel gauge. If complaint is not a malfunctioning fuel gauge, go to next step.
8. If complaint is poor fuel economy, see the TESTS W/O CODES article. If complaint is not poor fuel economy, go to next step.
9. If any other driveability symptoms exist, go to FUEL SYSTEM PRESSURE TEST under «BASIC FUEL SYSTEM CHECKS»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__basic-fuel-system-checks) . If other driveability symptoms do not exist, fuel system is okay.
10. Attempt to duplicate fuel leak or odor complaint. If a fuel leak is found, go to step 12). If a fuel leak is not found, see the TESTS W/O CODES article.
11. Attempt to duplicate fuel odor complaint. If fuel odor is found, see the TESTS W/O CODES article. If fuel odor is not found, fuel system is okay.
12. Repair fuel leak. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) .

BASIC FUEL SYSTEM CHECKS

Fuel Pressure Relief

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

1. 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. See FUEL PRESSURE RELIEF. Connect Fuel Pressure Gauge (J-34730-1) to fuel pressure fitting on fuel rail. Turn ignition on with engine off. Fuel pressure should be within specification. See «FUEL PRESSURE»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l) table. If no fuel pressure is present, go to step 5).
2. Start engine. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). Turn ignition off. Pressure should hold. If fuel pressure does not hold, check for leaking injectors or fittings. If injectors or fittings are not leaking, replace fuel pressure regulator.
3. If fuel pressure is less than specified, 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 the 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. Using a 10-amp fused jumper wire, apply battery voltage to fuel pump test connector. For location of fuel pump test connector, see COMPONENT LOCATIONS in the 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 the SYSTEM/COMPONENT TESTS article.

FUEL PRESSURE

Fuel Pump Relay

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

Fuel Pump Relay By-Pass Procedure

See FUEL DELIVERY in the SYSTEM/COMPONENT TESTS article.

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 the WIRING DIAGRAMS article. If battery voltage is not present, check ignition or PCM fuse. If fuse is not blown, check for open between fuse and ignition control module.

Ignition Coil Resistance

If ignition coil is suspected of causing misfire or no-spark condition, switch coil locations on ignition control module. If problem follows questionable coil, check ignition coil resistance or replace original coil. For ignition coil resistance, see IGNITION COIL RESISTANCE table.

IGNITION COIL RESISTANCE

Crankshaft Position (CKP) Sensor Pick-Up Coil Short & Resistance Checks

1. Set DVOM on 2000-ohm scale position. Connect DVOM leads to CKP sensor connector located on side of engine block. Turn ignition off. Disconnect ignition control module connectors. Check resistance between CKP sensor terminals at ignition control module connector.
2. CKP sensor resistance should be within specification range. See CRANKSHAFT POSITION (CKP) SENSOR RESISTANCE table. If resistance is not as specified, replace CKP sensor. If sensor is within specification, go to next step.
3. With CKP sensor installed in block, connect one ohmmeter lead to either sensor terminal at ignition control module. Touch other lead of ohmmeter to engine block. No continuity should exist. If continuity exists, CKP sensor is shorted to ground and must be repaired or replaced.

CRANKSHAFT POSITION (CKP) SENSOR RESISTANCE (1)

Crankshaft Position (CKP) Sensor Output Signal

Set DVOM on 2-volt AC scale. Connect DVOM leads to CKP sensor located on side of engine block. Crank engine and observe voltmeter reading. CKP sensor should generate a voltage signal of about 2 volts.

Tach Pulse (RPM) Signal

Connect scan tool to DLC. RPM should be indicated on scan tool when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance connected to ground) is used to backprobe RPM high reference circuit. For circuit and terminal identification, See the WIRING DIAGRAMS article.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see the 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) 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. Check if Malfunction Indicator Light (MIL) is illuminated with engine running, for driveability concerns, or faulty computer-controlled components. If problem is found, go to next step.
2. Ensure battery is fully charged. 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»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__dlc-diagnosis-or-no-scan-tool) .
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»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__no-start-diagnosis) .
4. Using scan tool, observe DTC status: MIL REQUEST, FAIL THIS IGN, LAST TST FAIL and HISTORY. If any DTC status is present, refer to affected DTC to diagnose problem. See the TESTS W/CODES article. If DTCs are not present, go to next step.
5. 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»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. Check all PCM power and ground connections and circuits. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . If connections and circuits are okay, go to next step.
3. Ensure battery is fully charged. Using DVOM, measure voltage between DLC battery feed circuit and DLC ground circuits. See the WIRING DIAGRAMS article. Voltage reading for both circuits should be 10 volts. If voltage readings are the same or higher for both circuits, go to step 7). If voltage readings are not the same or higher for both circuits, go to next step.
4. Using DVOM, measure voltage between ground and DLC battery feed circuit. See the WIRING DIAGRAMS article. Voltage reading should be 10 volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 6).
5. Repair open in DLC ground circuit that had low or no voltage. After repairs, go to step 7).
6. Repair open or short to ground in DLC battery feed circuit. Replace blown fuse as necessary. After repairs, go to next step.
7. Turn ignition on. If scan tool displays PCM data, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . If scan tool does not display PCM data, go to next step.
8. 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 13).
9. Reinstall scan tool on original vehicle and enter on-board diagnostics. If on-board diagnostics is entered, go to next step. If on-board diagnostics cannot be entered, diagnose vehicle computer system.
10. Using on-board diagnostics display, check all control modules for Diagnostic Trouble Codes (DTCs). If DTCs are present, see the TESTS W/CODES article for related DTC diagnosis. If DTCs are not present, go to next step.
11. Check for open in class 2 serial data circuit between DLC and PCM. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . If circuit is okay, go to next step.
12. Check DLC terminal connection. Repair as necessary. Exit on-board diagnostics. Reconnect scan tool. If scan tool displays PCM data, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) . If scan tool does not display PCM data, go to step 14).
13. Replace faulty scan tool. After scan tool replacement, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-obd-system-check) .
14. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/eldorado/x-1992-2002/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__on-board-diagnostic-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 the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.

See also:
• ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
• NO START - ENGINE CRANKS OKAY
• BASIC FUEL SYSTEM CHECKS
• FUEL PRESSURE
• NO START DIAGNOSIS
• DLC DIAGNOSIS OR NO SCAN TOOL DATA