Engine Controls - Basic Engine Testing 4.6l Cadillac DeVille Concours

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 the following articles

1. «SPECIFICATIONS»(ref-20208) - Eldorado
2. «SPECIFICATIONS»(ref-20213) - Except Eldorado

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. 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»(/cadillac/deville-concours/1994-1998/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, P1376, P1631, P1632 or P1634 is present, diagnose DTC(s) first. See TESTS W/CODES article. If DTC(s) are not present, go to next step.
3. Check all PCM ground points. Ground points are located on engine bracket on right front of engine, on DIS bracket, on right front cylinder head and on negative battery cable, under rear seat. Repair as necessary. After repairs, go to step 6). If ground circuits were okay, go to next step.
4. Check fuel system. Go to FUEL SYSTEM test or see «BASIC FUEL SYSTEM CHECKS (A-7)»(/cadillac/deville-concours/1994-1998/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__basic-fuel-system-checks-a-7). Repair as necessary. After repairs, go to step 6). If fuel system is okay, go to next step.
5. Diagnose DTC(s) present and cleared. See TESTS W/CODES article. Disconnect IC module connector terminal C3. (Scheme 2) Turn ignition on. Check voltage between IC module C3 connector and IC module terminal "C" (Pink wire). Voltage reading should be about 10 volts. If voltage reading is as specified, perform DTC P0322 diagnosis. If voltage reading is not as specified, check for open or short in Pink wire or faulty ignition feed fuse.
6. Start engine. If engine starts, perform OBD system check. If engine still does not start, go to next step.
7. Check engine mechanical condition causing a no-start condition. Check timing chain or valve timing. Repair as necessary. After repairs, perform OBD system check.

Scheme 2

Fuel System

Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure and capacity. See BASIC FUEL SYSTEM CHECKS (A-7) in this article and INJECTOR BALANCE/COIL TEST in SYSTEM/COMPONENT TESTS article. If a DTC is present, diagnose DTC. See TESTS W/CODES article.

Scheme 3

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»(/cadillac/deville-concours/1994-1998/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l) 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

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.

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, NOT on wire.
2. Using Spark Tester (ST-125), check for spark at each spark plug wire using spark tester. 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 Pink/Black or Pink wire of ignition module for battery voltage. If battery voltage is not present, check ignition or PCM fuse. If fuse is not blown, check for open between fuse and ignition module.

IGNITION COIL RESISTANCE

If ignition coil is suspected of causing misfire or no-spark condition, switch coil locations on DIS 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 module connectors. Check resistance between CKP sensor terminals at ignition module connector.
2. CKP sensor resistance should be within specification range listed in 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 module. Touch other lead of ohmmeter to engine block. No continuity should exist. If continuity exists, sensor or harness is shorted to ground and must be repaired or replaced.

CRANKSHAFT SENSOR RESISTANCE

CRANKSHAFT SENSOR OUTPUT SIGNAL

Set DVOM on 2-volt AC scale. Connect voltmeter leads to crankshaft sensor installed in side of engine block. Crank engine and observe voltmeter reading. Crank angle sensor should generate a voltage signal of about .05 volt at slow cranking speed to greater than .1 volt at high cranking speed. With engine running, voltage signal will be much greater.

TACH PULSE (RPM) SIGNAL

Connect scan tool to DLC. RPM should be indicated on tester 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) is used to backprobe RPM "high reference" circuit. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY .

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. Wait about 5 seconds. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, diagnose problem using DTC P1641. See TESTS W/CODES article.
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. Using scan tool in MISC TESTS function, select MIL OUTPUT TEST. Command MIL to turn off, using scan tool. If MIL turns off when commanded, go to next step. If MIL does not turn off when commanded, diagnose problem using DTC P1641. See TESTS W/CODES article.
4. 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)»(/cadillac/deville-concours/1994-1998/remont/testing-diagnostics/#engine-controls-basic-engine-testing-46l__no-start-diagnosis-a-3) .
5. 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 4

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

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/deville-concours/1994-1998/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. 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:
• ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
• NO START - ENGINE CRANKS OKAY
• BASIC FUEL SYSTEM CHECKS (A-7)
• PCM REPLACEMENT CHECK
• FUEL PRESSURE
• NO START DIAGNOSIS (A-3)