Engine Controls - Basic Testing - 5.0L: Other Ford Mustang IV

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 specification 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 oxygen 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

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 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 (service port) 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 150

1. Release fuel pressure. See FUEL PRESSURE RELEASE. Install fuel pressure gauge. Connect a jumper wire between fuel pump test terminal at the Data Link Connector (DLC) and ground. (Scheme 150) Turn ignition on, but DO NOT start engine. This activates the fuel pump.
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»(ref-123321) article. Turn ignition off and monitor fuel pressure for one minute. Fuel pressure should not drop more than 5 psi (34 kPa).
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 additional fuel system testing information, see the SYSTEM/COMPONENT TESTS - EEC-IV (5.0L) article. See the TESTS W/CODES - EEC-IV (5.0L) article in the ENGINE PERFORMANCE section for diagnostic procedure of PCM-controlled fuel pump circuits.

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 Resistance

Disconnect injector harness connectors. Using digital ohmmeter, measure resistance between injector terminals. If resistance is not 11-19 ohms, replace injector.

Note. For additional testing and information, see FUEL SYSTEM in the SYSTEM/COMPONENT TESTS - EEC-IV (5.0L) article.

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. INERTIA FUEL SHUTOFF (IFS) SWITCH LOCATION Application Location Mustang Lower Left Rear Of Trunk
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 the «WIRING DIAGRAMS - 5.0L»(ref-23191) article in the ENGINE PERFORMANCE section. Continuity should not exists. Reset switch and ensure continuity exists between appropriate terminals.

IGNITION CHECKS

Note. For circuit identification, see wiring diagram in the WIRING DIAGRAMS - 5.0L article in the ENGINE PERFORMANCE section.

Note. If an ignition failure occurs, ignition system may operate with limited ability using Failure Mode Effects Management (FMEM). When this occurs, trouble codes should be present, engine may be hard to start and dwell, and timing will not change.

Note. To identify ignition system type by application, see the ENGINE/VIN ID article in ENGINE PERFORMANCE.

IGNITION COIL RESISTANCE

V8 IGNITION COIL RESISTANCE

Spark Check

1. Perform self diagnostic QUICK TEST to check for ignition-related fault codes, and repair as necessary. See QUICK TEST in the «TESTS W/CODES - EEC-IV (5.0L)»(ref-23127) article in the ENGINE PERFORMANCE section. If no fault codes are retrieved, check ignition system wiring harness connectors for damage, corrosion and tight fit. See the «WIRING DIAGRAMS - 5.0L»(ref-23191) article in the ENGINE PERFORMANCE section.
2. If no fault codes are retrieved and vehicle starts, problem is intermittent. Go to «TESTS W/O CODES - EEC-IV (5.0L)»(ref-23230) article in the ENGINE PERFORMANCE section. If no fault codes are retrieved and vehicle has a no-start condition, 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 resistance is not as specified, and retest. If spark is still not present after servicing coil wire, see the appropriate «SYSTEM/COMPONENT TESTS - EEC-IV (5.0L)»(ref-23126) article in the ENGINE PERFORMANCE section.
4. 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 «TESTS W/O CODES - EEC-IV (5.0L)»(ref-23230) article in the ENGINE PERFORMANCE section.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see the ADJUSTMENTS - 5.0L article in the ENGINE PERFORMANCE section.

IGNITION TIMING

V8 BASE IGNITION TIMING

IDLE SPEED

Engine idle RPM is controlled by Idle Speed Control (ISC) solenoid and cannot be changed by standard adjustments. For further information, see the ADJUSTMENTS - 5.0L article in the ENGINE PERFORMANCE section.

IDLE SPEED SPECIFICATIONS

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to the TESTS W/CODES - EEC-IV (5.0L) article. If no hard codes are found in self-diagnostics, proceed to the appropriate TESTS W/O CODES - EEC-IV (5.0L) article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.