INTRODUCTION
The first step in diagnosing any driveability problem is to verify that the problem exists. This may be accomplished by test driving the vehicle under the conditions during which the problem reportedly occurs.
Prior to entering self-diagnostics, a careful and complete inspection of several systems is required. Most driveability or "no start" problems are not related to computerized engine control systems, but are in fact simple mechanical, electrical, fuel or vacuum related faults. Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged or misrouted vacuum hoses.
Before considering the computer system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in improper diagnosis or lost diagnostic time.
VISUAL INSPECTION
Perform a visual inspection of all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Inspect electrical connectors and connections for tight fit and corrosion. Repair as necessary. Inspect all vacuum hoses for proper routing, cuts or pinches. If necessary, See VACUUM DIAGRAMS . Repair as necessary. Inspect air induction system for possible vacuum leaks.
COMPRESSION
Engine mechanical condition can be checked using a compression gauge, vacuum gauge, or an engine analyzer capable of performing a relative compression test. See engine analyzer instruction manual for availability and description of relative compression feature.
| CAUTION | Use a remote starter to crank engine during compression test, NOT the ignition switch. The fuel injectors on many fuel injected models are triggered during the cranking mode. This could cause a fire hazard, flooding, crankcase contamination, hydrostatic lockup, or lubrication to be washed off of cylinder walls. |
EXHAUST SYSTEM BACKPRESSURE
The exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove O2 sensor or air injection check valve, if equipped. Connect a 1-10 psi gauge and run engine at 2500 RPM. If exhaust system backpressure is over 1 3/4-2 psi, exhaust system or catalytic converter is plugged.
If a vacuum gauge is used, connect it to intake manifold vacuum. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge slowly drops after stabilizing, exhaust system should be checked for a restriction.
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FUEL INJECTED MODELS
| CAUTION | High fuel pressure may be present in fuel lines and component parts on some models. Relieve pressure before attempting to open system for testing or component replacement. Do not allow fuel to flow onto engine or electrical parts or allow an open flame in area while testing fuel system components. |
- For no-start condition, see MPFI and SPFI FUEL PUMP CIRCUIT TEST. To check for proper fuel pressure on running engine go to step 2).
- Disconnect fuel pump connector. Crank engine for at least 5 seconds. If engine starts, let run until it stops. Disconnect fuel hose at pressure regulator and install fuel pressure gauge using "T" fitting.
- Start engine and check fuel pressure at idle. See REGULATED FUEL PRESSURE table. Increase engine RPM and make sure fuel pressure increases.
| Application | At Idle psi (kg/cm 2 ) |
|---|---|
| MPFI | 26-30 (1.8-2.1) |
| SPFI | 20-24 (1.4-1.7) |
REGULATED FUEL PRESSURE
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4-CYLINDER IGNITION TIMING
| Application | Man. Trans. | Auto. Trans. |
|---|---|---|
| 1.8L | 20 @ Idle | 20 @ Idle |
4-CYLINDER IGNITION TIMING (Degrees BTDC @ RPM)
6-CYLINDER IGNITION TIMING
| Application | Auto. Trans. | Man. Trans. |
|---|---|---|
| 2.7L | 20 @ 750 | 20 @ 750 |
6-CYLINDER IGNITION TIMING (Degrees BTDC @ RPM)
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SUMMARY
If no faults were found while performing BASIC TESTING, proceed to TESTS W/CODES article. If no hard codes are present, proceed to TESTS W/O CODES for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.), or intermittent diagnosis procedures.