INTRODUCTION
The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.
The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.
Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control 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. See VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section to verify routing and connections (if necessary). 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 manual for specific instructions.
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system. |
| Application | Pressure psi (kg/cm 2 ) |
|---|---|
| Normal Compression | 142-171 (10-12) |
| Minimum Compression | 114 (8.0) |
ENGINE COMPRESSION
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, 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 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.
If a vacuum gauge is used, 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 system component. DO NOT allow fuel to contact engine or electrical components. |
Basic diagnosis of fuel system should begin with determining fuel system pressure.
Fuel Pump Performance Test
Manufacturer does not supply delivery (volume/time) specification. For fuel pump pressure, see FUEL PUMP SPECIFICATIONS table.
| Application | Pressure psi (kg/cm 2 ) | Min. Vol. in 30 sec. Pts. (L) |
|---|---|---|
| Amigo & Pickup | 3.56 (.25) | Information is not available from manufacturer. |
FUEL PUMP SPECIFICATIONS
SPARK
Check for spark at coil wire and at each spark plug wire using a high output spark tester. Check spark plug wire resistance on suspect wires. Resistance should be within specification. See HIGH TENSION WIRE RESISTANCE table.
| Application | Ohms |
|---|---|
| Coil Wire | 2000-4700 |
| Spark Plug Wires | 9600-22,400 |
HIGH TENSION WIRE RESISTANCE
IGNITION COIL POWER SOURCE
Turn ignition on. Using voltmeter, check voltage between terminal "B" of coil (Black/Yellow wire) and ground. If battery voltage is not present, check fuse No. 9 in fuse box.
Ignition Coil Resistance Test
Using an ohmmeter, measure resistance as indicated in IGNITION COIL RESISTANCE table. (Scheme 1) If resistance is not within specification, replace ignition coil.
| Test (Terminals) | Ohms @ 68°F (20°C) |
|---|---|
| Primary (C & E) | 1.2-1.4 |
| Secondary (C & D) | 8600-13,000 |
| Insulation (C & Coil Body) | More Than 10,000,000 |
IGNITION COIL RESISTANCE
Scheme 1
AIR GAP
Use a non-metallic feeler gauge to adjust air gap. (Scheme 2) Loosen screws, and move ignitor to adjust air gap to.012-.020 In. (.30-.51 mm). Tighten screws, and recheck gap.
Scheme 2
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedure, see appropriate ADJUSTMENTS article in the ENGINE PERFORMANCE Section.
| Model | (1) RPM |
|---|---|
| Amigo & Pickup | 900 |
| (1) Use underhood emissions label specification if different than table. | |
| (1) | Use underhood emissions label specification if different than table. |
IDLE SPEED SPECIFICATIONS
| Application | (1) Base Timing |
|---|---|
| Amigo & Pickup | 6 @ 900 |
| (1) With distributor vacuum advance hose disconnected and plugged. | |
| (1) | With distributor vacuum advance hose disconnected and plugged. |
IGNITION TIMING (Degrees BTDC @ RPM)
SUMMARY
If no faults were found while performing BASIC TESTING , proceed to TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to appropriate 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.