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H TESTS W O CODES 1992 ENGINE PERFORMANCE Jaguar Trouble Shooting No Codes

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H - TESTS W/O CODES 1992 ENGINE PERFORMANCE Jaguar Trouble Shooting - No Codes


Jaguar XJS 1992 - INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform the Basic Diagnostic Procedures in 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 (ECU). 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. 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 the article SYSTEM/COMPONENT TESTS in this section. For related specifications, see the SPECIFICATIONS . For adjustment procedures, go to the following:


Jaguar XJS 1992 - SYMPTOMS SYMPTOM DIAGNOSIS


Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure basic diagnostic procedures in the BASIC TESTING article and the TESTS W/CODES article were performed before diagnosing a symptom. Symptoms available for diagnosis include:

  • Difficult To Start
  • Engine Backfires
  • No Power
  • Rough Or Unstable Idle

Jaguar XJS 1992 - 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 XJS 1992 - ENGINE BACKFIRES


  • Check for excessively lean air/fuel mixture.
  • Check for an air intake leak. (Idle speed will usually be faster if 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 XJS 1992 - 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 XJS 1992 - ROUGH OR 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 air leak is present.)
  • Check for air leaking into or out of exhaust system.

Jaguar XJS 1992 - INTERMITTENTS 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 circuit resistance. Status changes on DVOM during test procedures indicate area of fault.


Jaguar XJS 1992 - 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.