INTRODUCTION
Before proceeding with basic diagnostic procedures, ensure testing procedure is followed, as some systems which may result in a no-start condition may cause a Diagnostic Trouble Codes (DTC) to be stored in the Engine Control Module (ECM). See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
If no-start condition still exists after checking and repairing all DTCs, perform a careful and complete visual inspection. Many 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. 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 user manual for specific instructions. Engine compression ratio for 4.0L and 4.6L engines should be 9.35:1. Engine compression ratio specification is displayed above engine identification code. Engine identification code is stamped on a cast pad located between cylinders No. 3 and No. 5. (Scheme 8)
Scheme 8
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter switch to crank engine. Fuel injectors and fuel pump are activated by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system. |
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove front HO2S and connect a 0-5 psi pressure gauge. Start engine and run 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, exhaust system should be checked for a restriction.
FUEL PRESSURE
| WARNING | Always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
Note. Fuel pressure may be released at fuel rail or fuel filter fittings.
Relieving Fuel Pressure
Position shop towel around appropriate fitting to protect against fuel spray. Carefully loosen appropriate fitting. When fuel pressure has been released, tighten fitting.
Regulated Fuel Pressure
Regulated fuel pressure should be 35-37 psi (2.4-2.6 kg/cm 2 ). Pressure will vary depending on amount of intake manifold vacuum acting on fuel pressure regulator.
FUEL INJECTOR RESISTANCE
| Application | Ohms |
|---|---|
| 4.0L & 4.6L | 15.7-16.7 |
| (1) Specifications in ohms @ 68°F (20°C). | |
| (1) | Specifications in ohms @ 68°F (20°C). |
FUEL INJECTOR RESISTANCE (1)
SPARK
Check for spark at each spark plug wire using a high output spark tester. Check suspect spark plug wires for fraying, chafing, deterioration and/or opens. Specific resistance for each wire not available.
IGNITION COIL RESISTANCE
Remove primary and secondary leads from ignition coils. Using ohmmeter, check resistance of primary coils and secondary coils between positive and negative terminals of each coil. Refer to IGNITION COIL RESISTANCE . Replace faulty coil if resistance is not as specified.
| Application | Primary | Secondary |
|---|---|---|
| 4.0L & 4.6L | 0.80 | 12,000-14,600 |
| (1) Specifications in ohms @ 68°F (20°C). | ||
| (1) | Specifications in ohms @ 68°F (20°C). |
IGNITION COIL RESISTANCE (1)
IDLE SPEED & MIXTURE
Note. Engine idle speed and mixture are controlled by ECM based on signals from various sensors. Engine idle speed and mixture are not adjustable. Values given in IDLE SPEED & MIXTURE SPECIFICATIONS are for verification purposes only. Always refer to SERVICE INFORMATION underhood label in engine compartment. If underhood label differs from these specifications, always use underhood label specifications.
| Application | Specification |
|---|---|
| Base Idle Speed | 680-720 RPM |
| CO @ Idle | (1) |
| (1) Information not available. | |
| (1) | Information not available. |
IDLE SPEED & MIXTURE SPECIFICATIONS
IGNITION TIMING
Note. Ignition timing is controlled by ECM based on signals from Knock Sensor (KS), Crankshaft Position (CKP) sensor and Camshaft Position (CMP) sensor. No adjustment is possible.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate SELF DIAGNOSTICS article. If no hard codes are found in self-diagnostics, (if vehicle has self-diagnostic system) proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.
See also:
• IGNITION COIL RESISTANCE