Jaguar XJ-S 1991 - H - TESTS W/O CODES ENGINE PERFORMANCE Trouble Shooting - No Codes

Jaguar XJ-S 1991 - INTRODUCTION

Before diagnosing any symptoms or intermittent fault conditionss, perform test procedures in both the BASIC TESTING and the TESTS W/CODES articles in this section. Use this article to diagnose driveability problems existing 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 electronic control unit. Check with manufacturer for latest chip or control unit application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, system test or an adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested.

NOTE:

For specific component or system test procedures, see the SYSTEM/COMPONENT TESTS article. For specifications, refer to the SPECIFICATIONS article. For tune-up procedures, refer to the ADJUSTMENTS article.

Jaguar XJ-S 1991 - SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem occurs at the time the vehicle is being tested. To reduce diagnostic time, make sure the test procedures in both the BASIC TESTING and the TESTS W/CODES articles were performed before diagnosing a symptom. Symptoms available for diagnosis include:see the SYMPTOM-TO-DIAGNOSIS MENU below.

Jaguar XJ-S 1991 - SYMPTOM-TO-DIAGNOSIS MENU

Jaguar XJ-S 1991 SYMPTOM-TO-DIAGNOSIS MENU

Symptom	Go To:
Difficult to Start - All Conditions	DIFFICULT TO START
Engine Backfires	ENGINE BACKFIRES
Loss of Power/No Power	NO POWER
Rough or Unstable Idle	ROUGH/UNSTABLE IDLE

Jaguar XJ-S 1991 - DIFFICULT TO START

• Check for starter motor rotating too slowly.
• Ensure ignition system is okay.
• Ensure fuel system is okay.
• Check for bad engine ground.
• Check for auxiliary air valve malfunction (XJS).
• Check for idle speed control valve malfunction (XJ6).
• Check coolant temperature sensor.

Jaguar XJ-S 1991 - ENGINE BACKFIRES

• Check for excessively lean air/fuel mixture.
• Check for an air intake leak. (Idle speed will usually be faster if an intake air leak is present.)
• Check for leaking air into or out of exhaust system.
• Check for air leakage past valve guides or valves.
• Ensure ignition timing is correct.
• Check for incorrect valve timing.
• Check for valves sticking open.

Jaguar XJ-S 1991 - NO POWER

• Check for burned or sticking valves.
• Check for incorrect valve clearance.
• Ensure fuel system is okay.
• Ensure engine compression is okay.
• Ensure ignition system is okay.
• Check for incorrect camshaft timing.
• Check for incorrect octane fuel.

Jaguar XJ-S 1991 - ROUGH/UNSTABLE IDLE

• Check for burned or sticking valves.
• Check for incorrect valve clearance.
• Ensure engine compression is okay.
• Check for blown head gasket.
• Ensure ignition system is okay.
• Ensure fuel system is okay.
• Check for an intake air leak. (Idle speed will usually be faster if an intake air leak is present.)
• Check for air leaking into or out of exhaust system.

Jaguar XJ-S 1991 - 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 (on some systems) 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 circuit resistance. Status changes on DVOM during test procedures indicate area of fault.

Jaguar XJ-S 1991 - TEST PROCEDURES INTERMITTENT SIMULATION

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

• Lightly vibrate component.
• Heat component.
• Wiggle or bend wiring harness.
• Spray component with water.
• Remove/apply vacuum source.

Monitor circuit/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.