Engine Controls - Basic Testing - 3.8L: 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.

Note. For additional fuel system testing information, see the SYSTEM & COMPONENT TESTING - EEC-V article. See the G - TESTS W/CODES - EEC-V (3.8L) article in the ENGINE PERFORMANCE section for diagnostic procedure of PCM-controlled fuel pump circuits.

1. 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. Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and increase engine speed to 2500 RPM. If engine will not start, cycle ignition switch several times. Record fuel pressure. For fuel pressure specifications, see «FUEL PRESSURE SPECIFICATIONS»(ref-123321) article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, see the «SYSTEM & COMPONENT TESTING - EEC-V»(ref-97371) article for fuel system diagnosis.
3. With fuel pressure gauge still installed, cycle ignition switch on and off several times. Record fuel pressure. If fuel pressure is at least 25 psi (172 kPa) after one minute with ignition off, system is capable of maintaining fuel pressure. If fuel pressure is not at least 25 psi after one minute with ignition off, test fuel injectors for leakage. See FUEL INJECTORS.

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 TESTING - EEC-V 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 - 3.8L»(ref-23194) 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 - 3.8L 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.

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-V (3.8L)»(ref-23111) article in the ENGINE PERFORMANCE section. If no fault codes are retrieved, check ignition system wiring harness connectors for corrosion and tight fit. See the appropriate «WIRING DIAGRAMS - 3.8L»(ref-23194) article in the ENGINE PERFORMANCE section. 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 strong and consistent at each spark plug (one spark per crankshaft revolution), ignition system is okay. If spark is not present, go to IGNITION SYSTEMS in the appropriate «SYSTEM & COMPONENT TESTING - EEC-V»(ref-97371) article in the ENGINE PERFORMANCE section.

IGNITION COIL RESISTANCE

V6 IGNITION COIL RESISTANCE

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see the ADJUSTMENTS - 3.8L article in the ENGINE PERFORMANCE section.

IGNITION TIMING

V6 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 - 3.8L 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-V (3.8L) article. If no hard codes are found in self-diagnostics, proceed to the appropriate TESTS W/O CODES - EEC-V (3.8L) article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.