Engine Controls - Tests W/o Codes Subaru XT I

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in BASIC TESTING and TESTS W/CODES article in the ENGINE PERFORMANCE Section. Use this section to diagnose driveability problems that exist when a hard fault code is not present.

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or comuter application.

Symptom checks are intended to direct the technician to malfunctioning component(s) so that further diagnosis may be performed. A "symptom" should lead to further testing of specific components or systems, or verification of adjustment specifications.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For verifying specifications, SPECIFICATIONS or ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS (CARBURETED - JUSTY)

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES articles in the ENGINE PERFORMANCE Section have been performed before diagnosing a symptom. Symptoms available for diagnosis include

1. Does not start - cold
2. Does not start - warm
3. Rough or unstable idle
4. Idle speed too high
5. Engine stalls
6. Improper engine operation/poor fuel mileage
7. Engine afterburn occurs
8. Engine backfires
9. Engine knocks

DOES NOT START - COLD

1. Check battery condition.
2. Ensure sufficient secondary spark is available.
3. Ensure ignition and valve timing are correct.
4. Verify choke valve is closed.
5. Ensure fuel level is at specified mark on carburetor sight glass.
6. Ensure fuel system pressure is correct.
7. Check for contaminated fuel.
8. Ensure correct vacuum hose routing.
9. Check slow fuel-cut solenoid valve operation. A click should be heard from solenoid valve as ignition switch is cycled on and off.
10. Check charcoal canister operation by clamping hose(s) shut. If problem discontinues, check vacuum hose routing.
11. Ensure exhaust system is not restricted.

DOES NOT START - WARM

1. Check battery condition.
2. Ensure sufficient secondary spark is available.
3. Ensure ignition and valve timing are correct.
4. Verify choke valve is open.
5. Ensure fuel level is at specified mark on carburetor sight glass.
6. Ensure fuel system pressure is correct.
7. Check for contaminated fuel.
8. Check for clogged fuel return hose.
9. Check for loose or clogged carburetor jets.
10. Check for fuel percolation.
11. Ensure correct vacuum hose routing.
12. Check float chamber vent solenoid operation.
13. Check slow fuel-cut solenoid valve operation. A click should heard from solenoid valve as ignition switch is cycled on and off.
14. Check charcoal canister operation by clamping hose(s) shut. If problem stops, check vacuum hose routing.
15. Ensure exhaust system is not restricted.

ROUGH OR UNSTABLE IDLE

1. Ensure there are no vacuum leaks.
2. Verify vacuum hose routing is correct.
3. Ensure idle adjustment is correct.
4. Ensure fast idle adjustment is correct.
5. Check vacuum choke break diaphragm.
6. Check choke valve operation.
7. Ensure fuel level is at specified mark on carburetor sight glass.
8. Check for fuel percolation.
9. Check PCV system operation.
10. Check EGR operation.
11. Verify ignition timing is correct.
12. Briefly remove spark plug wires individually to determine if problem can be isolated.
13. Check thermostatic air cleaner operation.

IDLE SPEED TOO HIGH

1. Check idle-up actuator vacuum hose routing.
2. Check fast idle cam for binding.
3. Check linkage for binding.
4. Check choke adjustment and operation.
5. Check throttle cable adjustment.
6. Check ignition timing.

ENGINE STALLS

1. Verify correct air cleaner intake control door operation.
2. Ensure correct choke adjustment and operation.
3. Check idle compensator operation.
4. Check idle mixture adjustment.
5. Ensure there are no vacuum leaks.
6. Check PCV system operation.
7. Check EGR valve operation.

POOR FUEL MILEAGE

1. Ensure there are no vacuum leaks.
2. Ensure ignition and valve timing are correct.
3. Verify choke valve is open (engine warm).
4. Ensure fuel level is at specified mark on carburetor sight glass.
5. Verify base timing is correct and timing advance system is functional.
6. Ensure sufficient secondary spark is available.
7. Check canister purge control valve operation.
8. Ensure engine has sufficient compression.
9. Ensure exhaust system is not plugged.
10. Check carburetor mixture control duty cycle using dwell meter.
11. Check engine for overheating or overcooling.

ENGINE AFTERBURN OCCURS

1. Ensure idle adjustment is correct.
2. Ensure automatic choke operation is correct.
3. Check for clogged carburetor main air bleed.
4. Ensure ignition timing is correct.
5. Check spark plug cables for poor contact.

ENGINE BACKFIRES

1. Ensure idle adjustment is correct.
2. Ensure automatic choke operation is correct.
3. Check for clogged carburetor main jet.
4. Ensure ignition timing is correct.
5. Check carburetor mixture control duty cycle using dwell meter.

ENGINE KNOCKS

1. Check for clogged carburetor main jet.
2. Ensure operation of ignition control unit is correct.
3. Check EGR valve operation.
4. Ensure ignition timing is correct.
5. Check for poor or contaminated fuel.
6. Check for carbon in combustion chamber.
7. Check engine for overheating.

Scheme 95

Scheme 96

Scheme 97

Scheme 98

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in "ON" position or engine is running. Ensure ignition switch is in "OFF" position or negative battery cable is disconnected when monitoring cirucit resistance. Status changes on DVOM during test procedures indicate area of fault.

INTERMITTENT SIMULATION

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove or apply a vacuum supply source.

Monitor component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.