Engine Controls - Basic Testing - v8 Lincoln Town Car II

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 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. 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 are not pinched or cut. See VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section 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. Compression pressures are considered within specifications if the lowest reading cylinder is within 75 percent of the highest reading cylinder.

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove O2 sensor or air injection check valve (if equipped). Connect a 0-5 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.

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.

PRELIMINARY CHECKS

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

1. Check battery condition.
2. Check all wiring and vacuum connections.
3. Check air cleaner and ducting.
4. Check state of tune.
5. Check fuel delivery system.
6. Check cooling system.
7. Check inertia fuel shutoff switch.
8. Check for hydrostatic lock (liquid in cylinder).
9. Check fuel tank contents and fuel gauge accuracy.
10. Check for dirt, water or other contamination in fuel.
11. Check fuel lines and fittings for leaks.
12. Check fuel delivery system for proper pressure and volume.
13. Check for inoperative fuel injectors.
14. Check for improperly installed electronic equipment such as CB radio, cellular telephone or stereo.

FUEL PRESSURE RELEASE

1. Remove fuel cap to release fuel tank pressure. Remove relief valve cap. Relief valve is located on fuel supply manifold. Using Fuel Pressure Gauge (T80L-9974-B), release fuel pressure from relief valve (Schrader valve).
2. If fuel pressure gauge is not available, disconnect electrical connector to IFS switch. For IFS switch location, see INERTIA FUEL SHUTOFF (IFS) SWITCH location table under INERTIA FUEL SHUTOFF (IFS) SWITCH. Crank engine for 15 seconds to reduce system pressure.

FUEL PRESSURE

Note. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article.

Scheme 1

1. Release fuel pressure. Install fuel pressure gauge. Connect a jumper wire between ground and fuel pump test terminal at the Data Link Connector (DLC). (Scheme 1) Turn ignition on, but DO NOT start engine. This activates the fuel pump. CAUTION: Do not activate fuel pump for long periods, or engine may hydrostatically (liquid) lock.
2. Measure and record Key On, Engine Off (KOEO) fuel pressure. Start engine. Measure and record Key On, Engine Running (KOER) fuel pressure. For fuel pressure specifications, see «FUEL PRESSURE SPECIFICATIONS»(/lincoln/town-car/ii-1989-1997/remont/specifications/#fuel-pressure-specifications) article. Turn ignition off and monitor fuel pressure for one minute. Fuel pressure should not drop more than 5 psi (kg/cm 2 ).
3. If fuel pressure is within specification, test is complete. If fuel pressure is not within specification, check fuel filter and lines for restriction(s). Repair or replace as necessary. If fuel pressure is still not within specification, install fuel pressure gauge (if removed). CAUTION: Inspect fuel system for leaks or damage before testing fuel pump.
4. Start engine and observe fuel pressure gauge. Gently squeeze fuel return hose. If fuel pressure increases while squeezing fuel return hose, replace fuel pressure regulator. If fuel pressure does not change while squeezing fuel return hose, check for plugged fuel inlet strainer or defective fuel pump. Repair as necessary.

Note. For fuel circuit test information, see G - EEC-IV TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Fuel Injector Check

1. Connect tachometer to engine. Run engine at idle. Disconnect and reconnect injectors individually. When disconnected, each injector should cause a momentary drop in engine speed of at least 100 RPM. Engine RPM drop should only be momentary as Powertrain Control Unit (PCM) will attempt to re-establish correct idle RPM.
2. Replace any injectors that do not cause sufficient drop in engine speed. When test is complete, check idle speed. Refer to emission control specifications on decal in engine compartment. See IDLE SPEED & IGNITION TIMING.

Fuel Injector

On sequential PFI engines, disconnect injector harness connectors. Using digital ohmmeter, check connector terminal resistance of each injector. If resistance is not 11-18 ohms, replace injector. On non-sequential PFI engines, disconnect injector bank harness connector. Check resistance of injector bank. See INJECTOR BANK RESISTANCE table. Repair wiring or any injector not within specification.

Note. For additional testing and information, see FUEL SYSTEM in appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

INERTIA FUEL SHUTOFF (IFS) 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 (IFS) SWITCH LOCATION table. CAUTION: DO NOT reset inertia switch until fuel system has been inspected for leaks. INERTIA FUEL SHUTOFF (IFS) SWITCH LOCATION Application Location Mark VIII Left Front Of Trunk Mustang Lower Left Center Of Trunk All Others In Trunk On Left Hinge Support Or Behind Trim Panel
2. To test inertia switch, turn ignition off. Remove inertia switch. Shake inertia switch to force switch into tripped position (switch open).Measure resistance between inertia switch terminal. See INERTIA SWITCH RESISTANCE table. Replace switch if resistance is incorrect, or if switch cannot be tripped.

INERTIA SWITCH RESISTANCE

IGNITION COIL RESISTANCE

IGNITION COIL RESISTANCE

Spark Output Check

1. Check the EI (low data rate) system (formally Distributorless Ignition System - DIS) for fault codes and repair if necessary. See QUICK TEST in G - EEC-IV TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no fault codes are retrieved, check ignition system wiring harness connectors for corrosion and tight fit. Clean or repair connectors as necessary.
2. If wiring and connectors are okay, use Neon Bulb Spark Tester (D89P-6666-A) to check for spark at each spark plug wire while cranking engine. If spark is consistent and equal at each spark plug (one spark per crankshaft revolution), ignition system is okay. If spark is not present, go to IGNITION SYSTEMS in I - ECC-IV SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

1. Check the EI (high data rate) system (formally Electronic Distributorless Ignition System - EDIS) for fault codes and repair if necessary. See QUICK TEST in G - EEC-IV TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no fault codes are retrieved, check ignition system wiring harness connectors for corrosion and tight fit. (Scheme 2) Clean or repair connectors as necessary.
2. If wiring and connectors are okay, use Neon Bulb Spark Tester (D89P-6666-A) to check for spark at each spark plug wire while cranking engine. If spark is consistent and equal at each spark plug (one spark per crankshaft revolution), ignition system is okay. If spark is not present, go to IGNITION SYSTEMS in I - ECC-IV SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 2

1. Check the DI system (formally Thick Film Ignition-IV (TFI-IV) system) for fault codes and repair if necessary. See QUICK TEST in appropriate G - EEC-IV TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no fault codes are retrieved, check ignition system wiring harness connectors for damage, corrosion and tight fit. (Scheme 3)or (Scheme 4).
2. If no fault codes are retrieved and vehicle will start, go to appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE Section. If no fault codes are retrieved and vehicle is a no-start, connect a high-output spark tester between ignition coil wire and engine ground. Check for spark at coil wire while cranking engine. A consistent Blue spark should be present.
3. If spark is present, go to step 4). If no spark is present, remove distributor cap and crank engine to ensure distributor rotates. If okay, check resistance of coil secondary wire. Resistance should be less than 7000 ohms per foot. Service coil wire if necessary and retest. If spark is not present, go to IGNITION SYSTEMS in I - ECC-IV SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
4. If a consistent Blue spark is present at coil wire during cranking, inspect distributor cap and rotor for cracks or carbon tracking. Service as necessary and test spark output at spark plugs. If spark is present at spark plugs and engine will not start, go to appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 3

Scheme 4

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

IGNITION TIMING

Note. Ignition timing is not adjustable on models with Electronic Ignition (low or high data rate).

BASE IGNITION TIMING

IDLE SPEED

Engine idle RPM is fixed and cannot be changed by standard adjustments. A scan tool must be used because control strategy and idle speed is controlled by Powertrain Control Unit (PCM). See IDLE SPEED in ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

IDLE SPEED SPECIFICATIONS

IDLE MIXTURE ADJUSTMENT

Note. Idle mixture is not adjustable. If idle mixture is incorrect,see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

THROTTLE POSITION (TP) SENSOR ADJUSTMENT

Note. For TP sensor adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are found in self-diagnostics, proceed to appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

See also:
• FUEL PRESSURE SPECIFICATIONS