Engine Controls - Basic Testing Subaru Legacy BC/BJ/BF

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.

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.

1. 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.
2. Start engine and check fuel pressure at idle. See the «REGULATED FUEL PRESSURE»(/subaru/legacy/bcbjbf-1989-1994/remont/testing-diagnostics/#engine-controls-basic-testing) table. Ensure fuel pressure increases as engine RPM increases.

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 appropriate HIGH TENSION WIRE RESISTANCE table below.

LEGACY HIGH TENSION WIRE RESISTANCE

LOYALE HIGH TENSION WIRE RESISTANCE

XT & XT6 HIGH TENSION WIRE RESISTANCE

Legacy

1. Disconnect 3-wire connector from ignition coil assembly. Using an ohmmeter, check resistance between terminals No. 1 and 2. (Scheme 28) This tests primary resistance of one coil.
2. Check resistance between terminals No. 2 and 3. This tests primary resistance of other coil. If resistance is not approximately 0.7 ohm for each coil, replace ignition coil assembly.
3. To test secondary resistance, connect one ohmmeter lead to secondary tower at one end of coil. Connect remaining ohmmeter lead to secondary tower at opposite end of same coil. Repeat test for other coil.
4. If resistance of each coil is not approximately 13,800 ohms (Hitachi brand coil) or 21,000 ohms (Diamond brand coil), replace ignition coil assembly.

Scheme 28

All Other Models

1. There are 2 2-wire connectors at ignition coil; disconnect the round connector. Check primary resistance between terminals. If resistance is not .81-.99 ohm, replace coil.
2. 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 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 the ENGINE PERFORMANCE Section.

IDLE SPEED SPECIFICATIONS

IGNITION TIMING (Degrees BTDC @ RPM)

SUMMARY

If no faults were found while performing BASIC TESTING , proceed to the 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.

Scheme 29

LOYALE, XT & XT6 IGNITION CONTROL SYSTEM TESTS

Note. Terminal references in the following test chart apply only to Loyale PFI, XT and XT6. When testing Loyale TBI, refer to TERMINAL CONVERSION table for correct terminal reference.

TERMINAL CONVERSION

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Scheme 35

Scheme 36

Scheme 37

Scheme 38

Scheme 39

Scheme 40

Scheme 41

Scheme 42

Scheme 43

Scheme 44

Scheme 45

Scheme 46

Scheme 47

See also:
• REGULATED FUEL PRESSURE