Engine Controls - Basic Diagnostic Procedures Mercury Grand Marquis IV

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. The first step in diagnosing any driveability problem is verifying the symptom(s) with a test drive under the conditions the problem reportedly occurred.

Before proceeding with diagnostics, check for applicable Technical Service Bulletins (TSBs). If there are no applicable TSBs, perform QUICK TEST under SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE to identify Diagnostic Trouble Codes (DTCs). If no DTCs are present or only pass codes are found during self-diagnostics and symptom is present, proceed to TROUBLE SHOOTING - NO CODES - EEC-V - CNG, FLEX-FUEL & GASOLINE article for diagnosis by symptom.

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 are not pinched or cut. Inspect air induction system for possible vacuum leaks.

Compression

Check engine compression with engine at normal operating temperature, all spark plugs removed (on dual plugs, remove exhaust side only), and throttle wide open. Ensure crankcase is full and oil is of correct viscosity. With compression gauge installed, use remote starter switch to crank engine. Crank engine at least 5 revolutions, and record highest reading. Repeat procedure for all cylinders, using approximately same number of revolutions. Lowest compression reading should not be less than 75 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (7 kg/cm 2 ).

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove oxygen sensor or air injection check valve (if equipped). Connect a pressure gauge. Typical exhaust back pressure (when measured near the exhaust manifold and at normal engine operating temperature) should not exceed 3 psi at idle and 8 psi at wide open throttle under load.

If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port. Start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

NO-START/NORMAL CRANK

After repairing a no-start condition on models with electric Secondary Air Injection (AIR) system, disconnect AIR solid state relay. Start and run engine until surplus fuel is used, and then reconnect relay. Disconnecting AIR solid state relay may set a Continuous Memory DTC. After repairs are completed, clear DTCs. See CLEARING CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

Preliminary Checks

Check Inertia Fuel Shutoff (IFS) switch. Check fuel pressure and quality (octane, winter/summer grade fuel, methanol, etc.). Check add-on alarm/anti-theft devices. Check wiring harness connectors. Check for disconnected or restricted air intake duct. Check fuses and relays.

Miscellaneous Component Or System Checks

Check the following

1. Check fuel and ignition systems. Go to TEST KB, step 85) (LS and Thunderbird), or go to TEST A, step 1) (all others) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.
2. Check exhaust system for restriction. Go to TEST HF, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.
3. Check engine mechanical condition. Check compression, camshaft, valve train components, etc. See appropriate article in ENGINES.

Engine Will Now Start & Run Normally At Part Throttle

If engine starts and runs only at part throttle, check Idle Air Control (IAC) system. Go to TEST KE, step 2) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

Additional Intermittent Testing

Go to TEST Z, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

Ensure following systems and components are in good condition and operating properly before diagnosing problems in fuel injection system

1. Check battery and charging system condition.
2. Check all wiring harness and vacuum connections.
3. Check air cleaner and ducting.
4. Check secondary ignition components.
5. Check fuel delivery system.
6. Check fuel tank contents and fuel gauge accuracy.
7. Check for dirt, water or other contamination in fuel.
8. Check fuel lines and fittings for leaks.
9. Check fuel delivery system for proper pressure and volume.
10. Check for inoperative fuel injectors.
11. Check cooling system.
12. Check Inertia Fuel Shutoff (IFS) switch.
13. Check for blown head gasket (liquid in cylinder).
14. Check for improperly installed electronic equipment such as anti-theft system, CB radio, cellular telephone or stereo.

FUEL PRESSURE RELEASE

Note. For fuel pressure release procedures on Natural Gas Vehicles (NGV), see appropriate REMOVAL & INSTALLATION article.

1. Remove fuel cap to release fuel tank pressure. Remove relief valve service port cap. Relief valve service port is located on fuel supply manifold. Using Fuel Pressure Gauge (T80L-9974-B ), release fuel pressure from Schrader valve.
2. If fuel pressure gauge is not available, disconnect electrical connector to Inertia Fuel Shutoff (IFS) switch. For IFS switch location, see «INERTIA FUEL SHUTOFF SWITCH LOCATION»(/mercury/grand-marquis/iv-2002-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) table. Crank engine with IFS disconnected for 15 seconds to reduce system pressure.

Natural Gas Engines

1. 1) Check Fuel Pressure Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Install Natural Gas Fuel Rail Pressure Gauge Tool Kit (134-00114) to fuel rail Schrader valve. Using scan tool, access FRP PID (if available) from PID/DATA MONITOR & RECORD menu. With ignition switch turned to ON position, record FRP sensor PID or fuel pressure gauge reading. Start engine and allow to idle. Again record FRP sensor PID or fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. Record FRP sensor PID or fuel pressure gauge reading. Compare measured fuel pressure to fuel pressure specification. See «FUEL PRESSURE SPECIFICATIONS»(/mercury/grand-marquis/iv-2002-2005/remont/specifications/#fuel-system-pressure-specifications) . If fuel pressure readings are within specification, turn ignition switch to OFF position and go to next step. If fuel pressure readings are not within specification, turn ignition switch to OFF position and go to TEST HB, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article for fuel delivery system diagnosis.
2. 2) Check Fuel System For Pressure Stability With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 2 times to pressurize fuel system (DO NOT start engine). Verify no external leaks are present. If fuel pressure does not remain within 10 psi (69 kPa) of highest fuel pressure reading after 2 minutes, go to TEST HB, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article for fuel delivery system diagnosis. If fuel pressure remains within 10 psi (69 kPa) of highest fuel pressure reading after 2 minutes, go to next step.
3. 3) Check Fuel System For Pressure Stability With Ignition Switch Turned To ON Position Using scan tool, access FRP PID (if available) from PID/DATA MONITOR & RECORD menu. If FRP PID is not available, ensure natural gas fuel rail pressure gauge tool kit is installed onto fuel rail Schrader valve. Cycle ignition switch from OFF to ON (DO NOT start engine). Monitor fuel pressure reading. If fuel pressure does not remain within 10 psi (69 kPa) of highest fuel pressure reading after 10 seconds, check for leaking fuel injectors or fuel pressure regulator. If fuel pressure remains within 10 psi (69 kPa) of highest fuel pressure reading after 10 seconds, fuel system is mechanically okay.

Gasoline Engines

1. 1) Fuel System Visual Inspection Visually inspect fuel system, including fuel lines, connections, injectors and electrical connections. Ensure Inertia Fuel Shutoff (IFS) switch is not tripped. Check condition of battery and fuses. Ensure fuel level in tank is sufficient.
2. 2) Check Fuel Pressure Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Release fuel system pressure. See «FUEL PRESSURE RELEASE»(/mercury/grand-marquis/iv-2002-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures__fuel-pressure-release) . Install fuel pressure gauge. Using scan tool, access OUTPUT TEST MODE. For additional information, see «OUTPUT TEST MODE»(/mercury/grand-marquis/iv-2002-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-cng-flex-fuel-gasoline) under ADDITIONAL SYSTEM FUNCTIONS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article. Command fuel pump ON and run fuel pump to obtain maximum fuel pressure. Record fuel pressure. Compare measured fuel pressure to fuel pressure specification. See «FUEL PRESSURE SPECIFICATIONS»(/mercury/grand-marquis/iv-2002-2005/remont/specifications/#fuel-system-pressure-specifications) . If fuel pressure is within specification, go to next step. If fuel system pressure is not within specification, go to TEST HC, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article for fuel delivery system diagnosis.
3. 3) Check Fuel Pressure Leakdown With fuel pressure gauge still installed, cycle ignition switch on and off several times. Record fuel pressure. After one minute with ignition off, fuel pressure should remain within 5 psi (34 kPa) of maximum fuel pressure. If fuel pressure remains within specification, system is capable of maintaining fuel pressure. If fuel pressure does not remain within specification, check for leaking fuel injectors or fuel pressure regulator.

Fuel Injector Resistance

Disconnect injector harness connectors. Using digital ohmmeter, measure resistance between injector terminals. See INDIVIDUAL INJECTOR RESISTANCE table. Replace any injector not within specification.

INDIVIDUAL INJECTOR RESISTANCE

Fuel Injector Check

Ensure engine mechanical condition is okay. Ensure no vacuum leaks exist and ignition system is operating properly. Start engine and allow to idle. If engine will not start, crank engine for 10 seconds. Using a stethoscope, listen for clicking sound at each injector. If clicking sound is heard, fuel injector is operating. If clicking sound is not heard, see TEST HD: MISFIRE DETECTION MONITOR under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

INERTIA FUEL SHUTOFF SWITCH

1. If IFS switch is tripped, engine cannot be restarted until switch is manually reset. To reset IFS switch, depress switch button. For IFS switch location, see «INERTIA FUEL SHUTOFF SWITCH LOCATIONS»(/mercury/grand-marquis/iv-2002-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) table.
2. To test IFS switch, turn ignition off. Remove IFS switch. Shake IFS switch to force it into tripped position (switch open). Check continuity between appropriate IFS switch terminals. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Continuity should not exist. Reset switch and ensure continuity exists between appropriate terminals.

INERTIA FUEL SHUTOFF SWITCH LOCATIONS

Note. If vehicle is a no-start, see NO-START/NORMAL CRANK under SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG, FLEX-FUEL & GASOLINE article or TEST A: NO-START in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

Before diagnosing problems in ignition system, ensure following systems and components are in good condition and operating properly

1. Battery.
2. Timing belt or chain.
3. Fuel delivery and injection system.
4. All wiring and vacuum connections.
5. Air cleaner and ducts.
6. Cooling system.

EDIS (DISTRIBUTORLESS) IGNITION SYSTEM

Note. Crown Victoria, Grand Marquis, LS, Marauder, Mustang (4.6L), Sable and Taurus (3.0L 4V), Thunderbird and Town Car use Coil On Plug (COP). COP faults should set a DTC. For additional COP testing, see TEST JF: INTEGRATED IGNITION COIL ON PLUG FAILURE in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

Note. For circuit identification, see ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

Spark Check

Always perform self-diagnostic QUICK TEST to check for ignition-related fault codes, and repair as necessary. See QUICK TEST in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article. If no fault codes are retrieved, check for proper spark at each cylinder, go to TEST JB, step 17) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article. If spark is not present, go to TEST A: NO-START in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

IGNITION COIL RESISTANCE

Note. Resistance values are not provided by manufacturer. For integrated ignition coil testing, see TEST JE: INTEGRATED IGNITION COIL FAILURE in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article. For integrated ignition Coil On Plug (COP) testing, see TEST JF: INTEGRATED IGNITION COIL ON PLUG FAILURE in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

IDLE SPEED & IGNITION TIMING

Note. Idle speed and ignition timing are not adjustable. If idle speed is incorrect, see TEST HU: AIR INTAKE SYSTEM and TEST KE: IDLE AIR CONTROL VALVE in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

IDLE MIXTURE ADJUSTMENT

Idle mixture is not adjustable. If idle mixture is incorrect, see TEST H: FUEL CONTROL in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

IGNITION TIMING

Note. On all models with distributorless electronic ignition, manufacturer does not recommend checking ignition timing, as faulty readings are common and timing is not adjustable.

BASE IGNITION TIMING

THROTTLE POSITION SENSOR ADJUSTMENT

Throttle Position (TP) sensor is not adjustable. If testing is necessary, see TEST DH: THROTTLE POSITION SENSOR in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article. If no fault codes are found in self-diagnostics, proceed to TROUBLE SHOOTING - NO CODES - EEC-V - CNG, FLEX-FUEL & GASOLINE article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

See also:
• QUICK TEST
• TROUBLE SHOOTING - NO CODES - EEC-V - CNG, FLEX-FUEL & GASOLINE
• FUEL PRESSURE SPECIFICATIONS
• NO-START/NORMAL CRANK
• INERTIA FUEL SHUTOFF SWITCH LOCATION
• FUEL PRESSURE RELEASE