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. Look 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. |
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. Remove O2 sensor or air injection check valve (if equipped).
Connect a 1-10 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 steadily. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.
FUEL PRESSURE CHECK
Basic diagnosis of fuel system should begin with determining fuel system pressure. If fuel pump is inoperative, see appropriate FUEL PUMP CIRCUIT TEST CHART in this article.
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. If connecting fuel pressure gauge to fuel system without using a "T" connector, DO NOT operate fuel pump for more than a few seconds. Operating fuel pump for longer than a few seconds under this condition damages fuel pump. |
CARBURETED
Disconnect fuel pressure hose from carburetor and install pressure gauge using a "T" connector. Turn ignition on. Fuel pump should run for 3 seconds and stop. Discharge volume should be .35 pint (.17 L) per 30 seconds.
FUEL-INJECTED
- Disconnect fuel pump connector. Crank engine for at least 5 seconds. If engine starts, let it 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 the «REGULATED FUEL PRESSURE»(/subaru/justy/i-1987-1995/remont/testing-diagnostics/#engine-controls-basic-testing) table. Ensure fuel pressure increases as engine RPM increases.
| Application | Psi (kg/cm 2 ) |
|---|---|
| Justy 1.2L PFI | 41.3 (2.9) |
REGULATED FUEL PRESSURE
IGNITION CHECKS
Note. For additional ignition system testing procedures, see appropriate IGNITION CONTROL SYSTEM TEST chart in this article.
SPARK
Check for spark at spark plug wires using a spark tester. Check resistance of each spark plug wire. Replace wire if resistance is not within specification. See HIGH TENSION WIRE RESISTANCE table.
| Application | Ohms |
|---|---|
| No. 1 | 458-10,680 |
| No. 2 | 411-959 |
| No. 3 | 290-676 |
| Coil | 459-10,710 |
HIGH TENSION WIRE RESISTANCE
IGNITION COIL RESISTANCE CHECK - JUSTY CARBURETED
- Disconnect 4-wire connector at ignition coil/power transistor assembly. Check primary resistance between terminals No. 2 and 3. (Scheme 5) If resistance is not.81-.99 ohm, replace coil.
- To check secondary resistance, connect ohmmeter between coil secondary tower and terminal No. 3 of 4-wire connector. If resistance is not 8500-11,000 ohms, replace coil.
Scheme 5
IGNITION COIL RESISTANCE CHECK - JUSTY PFI
- Disconnect ignition coil 2-wire connector. Check primary resistance between terminals. If resistance is not .81-.99 ohm, replace coil.
- To check secondary resistance, connect ohmmeter between coil secondary tower and White/Black wire terminal of 2-wire connector. If resistance is not 8500-11,000 ohms, replace coil.
CRANK ANGLE & TDC SENSOR SIGNALS TEST
Note. For crank angle and TDC sensor signal testing, see the TESTS W/CODES article in the ENGINE PERFORMANCE Section.
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see the ADJUSTMENTS article in this section.
| Application | (1) RPM | |
|---|---|---|
| Justy | ||
| 1.2L Carbureted | 750-850 | |
| 1.2L PFI | 650-750 | |
| (1) Transmission in Neutral. | ||
| (1) | Transmission in Neutral. |
IDLE SPEED SPECIFICATIONS
| Application | Degrees BTDC @ RPM | |
|---|---|---|
| Justy | ||
| 1.2L Carbureted | 5 @ 800 | |
| 1.2L PFI | 5 @ 700 | |
| (1) Connect test mode connector and ensure idle switch contacts are closed. | ||
| (1) | Connect test mode connector and ensure idle switch contacts are closed. |
IGNITION TIMING SPECIFICATIONS (1)
Scheme 6
Scheme 7
Scheme 8
Scheme 9
Scheme 10
Scheme 11
Scheme 12
Scheme 13
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 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.
See also:
• REGULATED FUEL PRESSURE