Jaguar XJ (X350). Service manual — part 36

100-04 : Noise, Vibration and Harshness

General procedures

Exhaust System Neutralizing

1. Loosen the muffler inlet pipe and resonator pipe to exhaust manifold fasteners at the
flanges and the muffler inlet connection.


2. Place a stand to support the muffler parallel to the vehicle frame with the muffler pipe
bracket free of stress.


3. Tighten the muffler connection.


4. Position the exhaust pipes to the manifolds and tighten. Make sure that the catalytic
converter and heat shield do not contact the frame rails.


5. With the complete exhaust system tight (and cooled) the rear hanger insulator should be
angled forward, to allow the system to expand rearward when heated during normal running

Description and operation

Noise, Vibration and Harshness (NVH)

Noise, vibration and harshness (NVH) is becoming more important as vehicles become more
sophisticated and passenger comfort levels increase. This section is designed to aid in the
diagnosis, testing and repair of NVH concerns.

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Noise is defined as sounds not associated with the operation of passenger
compartment equipment that interface with customer satisfaction.

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Vibration is defined as impulses felt by the customer that are not caused by road
surface changes.

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Harshness is a ride quality issue where the customer feels that the vehicle response to
the road surface is sharply transmitted to the customer.

Diagnostic Theory

Diagnosis is more than just following a series of interrelated steps in order to find the solution
to the specific condition. It is a way of looking at systems that are not functioning the way
they should and finding out why. Also it is knowing how the system should work and whether
it is working correctly.

There are basic rules for diagnosis. If these rules are followed, the cause of the condition is
usually found the first time through the system.

Know the System

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Know how the parts go together.

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Know how the system operates as well as its limits and what happens when the system
goes wrong.

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Sometimes this means checking the system against one that is known to be working
correctly.

Know the History of the System

A clue in any one of these areas may save time:

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How old or new is the system?

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What kind of treatment has it had?

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Has it been repaired in the past in such a manner that might relate to the present
condition?

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What is the repair history?

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Did it start suddenly or appear gradually?

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Was it related to some other occurrence such as a collision or previous part renewal?

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Know how the condition made itself known; it may be an important clue to the cause.

Know the Probability of Certain Conditions Developing

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Look for the simple rather than the complex.

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For example: Electrical conditions usually occur at connections rather than
components. An engine no-start is more likely to be caused by a loose wire or small
adjustment rather than a sheared-off camshaft.

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Electrical conditions usually occur at connections rather than components.

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An engine no-start is more likely to be caused by a loose wire or small
adjustment rather than a sheared-off camshaft.

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Know the difference between impossible and improbable. Certain failures in a system
can be improbable but still happen.

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New parts are just that, new. It does not mean they are always good functioning parts.

Do Not Cure the Symptom and Leave the Cause

Lowering the pressure in a front tire may correct the condition of a vehicle leaning to one
side, but it does not correct the original condition.

Be Positive the Cause is Found

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Double check the findings.

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What caused a worn component?

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A loose transmission or engine mount could indicate that other mounts are also loose.

Diagnostic Charts

Charts are a simple way of expressing the relationship between basic logic and a physical
system of components. They help discover the cause of a condition in the least time.
Diagnostic charts combine many areas of diagnosis into one visual display:

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probability of certain things occurring in a system

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speed of checking certain components or functions before others

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simplicity of carrying out certain tests before others

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elimination of checking huge portions of a system by carrying out simple tests

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certainty of narrowing down the search to a small portion before carrying out in-depth
testing

The fastest way to find a condition is to work with the tools that are available. This means
working with proven diagnostic charts and the correct special equipment for the system.

Know the History of the Condition

Diagnosis and testing

Noise, Vibration and Harshness (NVH)

Inspection and Verification

1 . Verify the customer's concerns by operating the vehicle to duplicate the condition.

2 . Visually inspect the vehicle to determine any obvious cause(s) of the concern(s).

3 . If the inspection reveals obvious causes that can be readily identified, repair as necessary.

4 . If the concern(s) remains after the inspection, determine the symptom(s) and go to the
Symptom Chart.

How To Use This Diagnostic Procedure Section

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Noise, vibration and harshness (NVH) concerns have become more important as
vehicles have become more sensitive to these vibrations. This section is designed as an
aid to identifying these situations.

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The section provides diagnostic procedures based on symptoms. If the condition
occurs at high speed, for instance, the most likely place to start is under High Speed
Shake.

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The road test procedure will tell how to sort the conditions into categories and how to
tell a vibration from a shake.

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A series of Road Test Quick Checks is provided to make sure that a cause is either
pinpointed or eliminated.

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Name the condition, proceed to the appropriate section and locate the correct
diagnosis. When the condition is identified, the job is partly done.

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Follow the diagnostic procedure as outlined.

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Quick Checks are described within the step, while more involved tests and
adjustments are outlined in General Procedures.

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Always follow each step exactly and make notes to recall important findings later.

Customer Interview

The road test and customer interview (if available) provide information that will help identify
the concerns and will provide direction to the correct starting point for diagnosis.

Identify the Condition

NVH problems usually occur in a number of areas:

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tires

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engine accessories

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