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.
Because fuel injectors on many models are triggered by 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 O[I2] 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 1 3/4 - 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
Before diagnosing problems in ignition system, ensure following systems and components are in good condition and operating properly.
- Battery
- State of tune
- Fuel delivery and injection system
- All wiring and vacuum connection
- Air cleaner and ducts
- Cooling system
DISTRIBUTORLESS IGNITION SYSTEM (DIS) 2.3L
Note. Following diagnostic tests are sequential. Beginning with first test, complete each successive test. DO NOT skip tests unless so directed.
ELECTRONIC DISTRIBUTORLESS IGNITION SYSTEM (EDIS) 4.0L ENGINE
Note. Following diagnostic tests are sequential. Beginning with first test, complete each successive test. DO NOT skip tests unless so directed.
| CAUTION | DO NOT connect EEC-IV ECA to EEC-IV breakout box while performing EDIS diagnosis unless so instructed. |
IGNITION COIL RESISTANCE
| Application | Primary | Secondary |
|---|---|---|
| DIS, EDIS | .5 | (1) |
| TFI-IV | 0.8-1.6 | 8000-11,500 |
| (1) Resistance values are not provided by manufacturer. | ||
| (1) | Resistance values are not provided by manufacturer. |
IGNITION COIL RESISTANCE
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 for starting and charging system problems.
Engine Cranks But Will Not Start
- Check fuel tank contents and fuel gauge accuracy. Check for dirt, water or other 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 problem.
- 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. 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
| CAUTION | 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 105) For additional circuit test information, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.
Scheme 105
Fuel Injector Check
- Connect tachometer to engine. Run engine at 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. When test is complete, turn engine off. To check curb idle, refer to emission control specifications on decal in engine compartment or IDLE SPEED & MIXTURE in ADJUSTMENTS article in the ENGINE PERFORMANCE Section.
Fuel Injector Circuit
Disconnect all injector harness connectors. Using digital ohmmeter, check resistance across terminals of each injector. See INDIVIDUAL INJECTOR RESISTANCE . Disconnect injector bank harness connector, and check resistance of injector bank. See INJECTOR BANK RESISTANCE . Repair injector bank or any injector not within specifications.
| Engine | Ohms |
|---|---|
| 2.3L & 3.0L | 15-18 |
| All Others | 13-16 |
| (1) Resistance values are for a single injector. | |
| (1) | Resistance values are for a single injector. |
INDIVIDUAL INJECTOR RESISTANCE (1)
| Engine | Ohms |
|---|---|
| 2.3L | 7.0-9.5 |
| 2.9L, 3.0L & 4.9L | 5.0-6.5 |
| 5.0L, 5.8L & 7.5L | 3.0-4.0 |
INJECTOR BANK RESISTANCE
Note. For further component testing and information, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.
INERTIA SWITCH
- 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 eventually 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 switches may be found in following locations: AEROSTAR & "E" SERIES - On right kick panel, just forward of door opening. BRONCO & "F" SERIES - On floorboard, left of and above steering column. EXPLORER - Under instrument panel, right of transmission hump.
| CAUTION | DO NOT reset inertia switch until inspecting fuel system for leaks. |
BASE IGNITION TIMING
Note. Base Ignition timing on the 2.3L models is not adjustable.
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section. Ensure all accessories are off and transmission is in Park or Neutral. Set parking brake. Disconnect automatic parking brake release (if equipped). Ensure vehicle front wheels are in straight-ahead position and curb idle speed set to specification.
Note. Ignition timing is not adjustable on models with DIS or EDIS.
| Application (1) | Degrees BTDC @ RPM |
|---|---|
| 4.9L | 10 @ (1) |
| (1) Information not available from manufacturer. Use Scan tool to set idle. | |
| (1) | Information not available from manufacturer. Use Scan tool to set idle. |
6-CYLINDER BASE IGNITION TIMING
| Application (1) | Degrees BTDC @ RPM | |
|---|---|---|
| 2.9L | ||
| Automatic Transmission | 10 @ 800 | |
| Manual Transmission | 10 @ 850 | |
| 3.0L | 10 @ (2) | |
| 4.0L | Timing not adjustable. | |
| (1) With SPOUT in-line connector disconnected. (2) Idle speed is not adjustable. | ||
| (1) | With SPOUT in-line connector disconnected. |
| (2) | Idle speed is not adjustable. |
V6 BASE IGNITION TIMING
| Application | (1) Degrees BTDC @ RPM | |
|---|---|---|
| 5.0L | ||
| Automatic Transmission | 10 @ 525-825 | |
| Manual Transmission | 10 @ 550-850 | |
| 5.8L | ||
| C6 Automatic Transmission | 10 @ 630-930 | |
| E4OD Automatic Transmission | 10 @ 580-880 | |
| Manual Transmission | 10 @ 580-880 | |
| 7.5L | 10 @ 500-800 | |
| (1) With SPOUT in-line connector disconnected. | ||
| (1) | With SPOUT in-line connector disconnected. |
V8 BASE IGNITION TIMING
IDLE SPEED
Idle speed is controlled by ECA and idle speed control air by-pass valve on all engines. If control system is operating properly, engine idle RPM is fixed and cannot be changed by standard adjustments. Manufacturer does not provide RPM specifications for many engines. A Scan tool must be used on these systems because control strategy and idle speed specification are controlled by ECA. See appropriate ADJUSTMENTS article in the ENGINE PERFORMANCE Section.
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 appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are found in self-diagnostics or if vehicle does not have a self-diagnostic system, proceed to 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.