Compression
Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer. If using engine analyzer, see engine analyzer manual for specific instructions. Compression pressures are considered within specifications if lowest reading cylinder is within 75 percent of highest reading cylinder. Minimum compression should be 128 psi (883 kPa). Maximum compression variation allowed between cylinders is 14 psi (97 kPa).
| WARNING | Because fuel injectors on many models are triggered by the ignition switch, DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine to prevent fire hazard or engine oiling system contamination. |
Exhaust System Backpressure
Using a vacuum or pressure gauge, check exhaust system. 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, and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restrictions.
PRELIMINARY CHECKS
Ensure following systems and components are in good condition and operating properly before diagnosing problems in fuel injection system.
- Battery
- State Of Tune
- Fuel Delivery System
- All Wiring And Vacuum Connections
- Air Cleaner And Ducts
- Cooling System
Engine Does Not Crank
Check for hydrostatic lock (liquid in cylinder). Repair as needed. Check starting and charging system.
Engine Cranks But Will Not Start
- Check fuel tank contents and fuel gauge accuracy. Check for dirt, water or contamination in fuel.
- Check ignition system for strong secondary current at spark plugs. If no spark exists or if spark is weak, repair ignition system.
- Check fuel lines and fittings for leaks. If no leaks are found, check fuel delivery system for proper pressure and volumes. Reset inertia switch (if necessary).
- Check for a defective fuel injector or coolant temperature sensor. Ensure TPS does not stick.
| WARNING | Always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
FUEL PRESSURE RELEASE
Disconnect negative battery cable. Remove fuel cap to release fuel tank pressure. Using EFI Pressure Gauge (T80L-9974-B), release fuel pressure from relief valve. Relief valve is located on fuel supply manifold.
FUEL PRESSURE
| WARNING | Inspect fuel system for leaks or damage before testing fuel pump. |
Note. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article.
Release fuel pressure. Install fuel pressure gauge. Fuel pump may be activated by grounding fuel pump lead at Self-Test connector. Using a jumper lead, ground FP terminal with ignition on. This activates fuel pump. (Scheme 99) See FUEL PUMP SPECIFICATIONS table. For additional testing information, see FUEL SYSTEM in SYSTEM/COMPONENT TESTS article in this section.
Scheme 99
| Application | Specification |
|---|---|
| Pressure | (1) |
| Volume | (2) |
| (1) For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. (2) Volume is 1 Pt. (.5L) in 30 Seconds. | |
| (1) | For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. |
| (2) | Volume is 1 Pt. (.5L) in 30 Seconds. |
FUEL PUMP SPECIFICATIONS
Fuel Injector Check
Connect tachometer to engine. Start engine and allow to idle. Disconnect and reconnect injectors individually. If each injector causes a momentary drop in engine speed of at least 100 RPM, injectors are providing proper fuel delivery. RPM drop should only be momentary, as ISC will attempt to re-establish correct idle RPM. Replace any injectors not causing sufficient drop in engine speed.
Fuel Injector Circuit
Disconnect all injector harness connectors. Using digital ohmmeter, check resistance across terminals of each injector. See INDIVIDUAL INJECTOR RESISTANCE table. Repair any injector not within specifications.
| Engine | Ohms |
|---|---|
| Bronco | 11-18 |
| (1) Resistance values are for a single injector. | |
| (1) | Resistance values are for a single injector. |
INDIVIDUAL INJECTOR RESISTANCE (1)
Note. For further component testing and information, see TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section.
INERTIA SWITCH
| WARNING | DO NOT reset inertia switch until fuel system has been inspected for leaks. |
- In event of a collision, electrical contacts in inertia switch open, automatically shutting off fuel pump. Fuel pump shuts off even if engine does not stop running. Engine will stops due to lack of fuel.
- Engine cannot be restarted until inertia switch is manually reset. To reset inertia switch, depress button on switch. Inertia switch may be found in the following location: On floorboard, left of and above steering column.
Definition
No-start is defined as engine cranks okay, but does not start. Engine may fire a few times.
Before diagnosing problems in ignition system, ensure following systems and components are in good condition and operating properly.
- Battery
- State Of Engine Tune
- Fuel Delivery And Injection System
- All Wiring And Vacuum Connections
- Air Cleaner And Ducts
- Cooling System
| Application | System |
|---|---|
| 5.0L & 5.8L | DI (CCD System "H") |
IGNITION SYSTEM APPLICATION
Spark Output Check
- Check for trouble codes stored in PCM and repair if necessary. See QUICK TEST in «TESTS W/CODES - EEC-IV»(ref-22952) article in this section. If no trouble codes are retrieved, check ignition system wiring harness connectors for corrosion and tight fit. Clean or repair connectors as necessary.
- 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 appropriate «SYSTEM/COMPONENT TESTS»(ref-22986) article in this section.
- Check for trouble codes stored in PCM and repair if necessary. See QUICK TEST in «TESTS W/CODES - EEC-IV»(ref-22952) article. If no trouble codes are retrieved, check ignition system wiring harness connectors for corrosion and tight fit. Clean or repair connectors as necessary.
- 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 appropriate «SYSTEM/COMPONENT TESTS»(ref-22986) article in this section.
- Check for trouble codes stored in PCM and repair if necessary. See QUICK TEST in «TESTS W/CODES - EEC-IV»(ref-22952) article in this section. If no trouble codes are retrieved, check ignition system wiring harness connectors for damage, corrosion and tight fit.
- If no fault codes are retrieved and vehicle will start, go to «TESTS W/O CODES»(ref-22970) article in this 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.
- 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 «SYSTEM/COMPONENT TESTS»(ref-22986) article in this section.
- 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 «TESTS W/O CODES»(ref-22970) article in this section.
IGNITION COIL RESISTANCE
| Application | Primary | Secondary |
|---|---|---|
| DI | 0.8-1.6 | 8000-11,500 |
IGNITION COIL RESISTANCE
BASE IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in this section. Ensure all accessories are off and transmission is in Park or Neutral. Set parking brake. Ensure vehicle front wheels are in straight-ahead position and idle speed is correct.
Note. Always refer to Emission Control Label in engine compartment before attempting service. If manual and label differ, always use emission label specifications.
| Application | Degrees BTDC |
|---|---|
| Bronco | (1) 10 |
| (1) With SPOUT in-line connector unplugged. | |
| (1) | With SPOUT in-line connector unplugged. |
BASE IGNITION TIMING
IDLE SPEED
Idle speed is controlled by PCM and idle speed control air by-pass valve on all engines. On most models, engine idle RPM is fixed and cannot be changed by standard adjustments. A scan tester must be used on these systems because control strategy and idle speed specification are controlled by PCM. See IDLE RPM SPECIFICATIONS.
Before performing idle speed adjustment procedure, complete a thorough basic inspection and self-test (KOEO, KOER, Continuous Memory self-tests) to confirm operation of sub-systems contributing to idle speed control. See QUICK TEST in TESTS W/CODES - EEC-IV article in this section.
| Application | RPM |
|---|---|
| Bronco | (1) ** |
| (1) Idle speed is computer controlled and is not adjustable. | |
| (1) | Idle speed is computer controlled and is not adjustable. |
IDLE RPM SPECIFICATION
THROTTLE POSITION (TP) SENSOR
| Application | Idle | Wide Open Throttle |
|---|---|---|
| 5.0L & 5.8L | 0.34 | 4.84 |
| (1) Minimum idle and maximum wide open throttle specifications are given. | ||
| (1) | Minimum idle and maximum wide open throttle specifications are given. |
TP SENSOR VOLTAGE SPECIFICATIONS (1)
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES - EEC-IV article in this section. If no hard codes are found in self-diagnostics or if vehicle does not have a self-diagnostic system, go to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.