Interior - Wind Noise Diagnosis
NO.: TSB-97-42A-001DATE: February, 1997
MODEL: All Models
SUBJECT:
WIND NOISE DIAGNOSIS
PURPOSE
As vehicle interiors become quieter, wind noise becomes more noticeable to the customer. Modern sealing techniques and smooth aerodynamic exteriors significantly reduce the causes of wind noise. Customer expectations of interior quietness require technicians to detect and correct even small wind noises. This bulletin describes common causes of wind noise and how to diagnose them.
Specific corrective actions may vary from model to model.
AFFECTED VEHICLES
All Mitsubishi models
CAUSES OF WIND NOISE
Wind noise may be created by:
^ Air turbulence as air flows over the vehicle
^ Aspiration as air enters or leaves the interior
^ Vibration of a vehicle part from force of air flowing over it
Air Turbulence
When air flows smoothly over a moving object, no noise is produced. If the smooth flow of air is disturbed by an edge, gap or projection, the air flow becomes turbulent and creates wind noise.
Aspiration
When a pressure difference exists between two spaces (such as between a vehicle's interior and exterior), any opening will allow air to move from a high pressure space to a lower pressure space. As the air flows from one space to another, aspiration noise is created. Common causes of aspiration noise are loose weatherstripping and partially open sunroof, doors or windows. Aspiration noise varies with vehicle speed and ventilation blower speed.
Vibration
Wind noise can also be caused by air flowing over a vehicle part and causing it to vibrate. Vibrating air intake grilles made of thin bars, radio antennas, outside mirrors, and loose or protruding body mouldings are common causes of wind noise.
DIAGNOSIS PROCEDURES
1. Ask the customer for details about the apparent location of the noise and the conditions under which the noise occurs. Try to determine the vehicle speed, weather conditions, and wind direction.
2. Test drive the vehicle under similar conditions with the customer. The technician should sit in the appropriate seat where the wind noise is most audible.
3. A stethoscope, ultrasonic leak detector or smoke generator can assist in detecting the source of an aspiration type of wind noise. A smoke generator and ultrasonic leak detector can be used when the vehicle is not moving.
NOTE:
Leak detectors and smoke generators cannot identity wind noise created by vibrating mouldings, air intake grilles or antennas. Diagnose this type of noise during test drives.
a. Leak detectors have a sound wave emitter and a receiver. Hold the emitter inside the vehicle with the doors closed. Sound waves from the emitter are picked up by a receiver being held outside the vehicle. Any gap in the vehicle's sealing provides a path for the sound waves to travel through.
b. With the heater/air conditioning blower on the highest setting with the outside air circulating, hold a smoke generator outside the vehicle near a suspected air leakage area. Visible air flow inside the vehicle will reveal where air leaks exist. Good light and calm air are important when using this method.
4. Determine whether any accessories or other easily removed parts could cause wind noise by vibrating as air flows over them. Antennas and roof racks are common accessories that may cause wind noise. If possible, test drive the vehicle again with the suspected accessory removed.
5. Note any non-factory sunroofs, roof racks and lights in the suspected wind noise area. Service manuals do not describe repair or adjustment of these items, and they are not covered by the Mitsubishi warranty. You may refer the customer to the aftermarket manufacturer.
6. On models with a sunroof, ensure that the sunroof is properly adjusted and closes securely.
7. On convertible models, ensure that the top is properly adjusted. The windshield header should not leak air into the interior. Side windows should seal securely against the top weatherstripping.
8. Apply removable tape over suspected interior and exterior areas. Then test drive the vehicle to determine whether the wind noise is eliminated.
If the noise is eliminated with the tape applied, remove the tape from one area at a time, test driving each time you remove the tape from a suspected area. By process of elimination, you can pinpoint the noise source.
COMMON WIND NOISE AREAS
1. Doors
a. Examine the weatherstrip for damage, deterioration, and improper installation. Rub some chalk on the weatherstrip, then close the door. When you open the door, a break in the chalk line on the door frame indicates an air leakage area. Repair or replace the weatherstrip.
b. Examine the door itself for misalignment or deformation. Adjust or replace as required.
2. Door Mirrors. If a door mirror is a suspected source of wind noise, disassemble the mirror. Examine it carefully for possible damage (e.g., cracks) that might create air leakage. Repair or replace as required.
3. Windows. Ensure that windows are properly aligned in their channels and the glass runs are sealed securely against the glass when the door is closed.
4. Body Weatherstripping
Body weatherstripping usually provides multiple barriers against leakage. A-Pillar weatherstripping has inner and outer seals in channels or pressed against body flanges. Where the door meets the center pillar, balloon sections compress when the door is closed. Lip sections support balloon sections and provide additional protection against leakage. Be sure the doors fit evenly with no gaps. Check for crushed balloon sections and weatherstripping out of its channel. Adjust or replace as needed.
5. Exterior Mouldings
On some vehicles, exterior stainless steel mouldings can cause wind or buzzing noise if not tightly fitted against the rubber retainer. Be sure they are firmly mounted.
The steel band must fit tightly into the rubber seal along its entire length.
6. Sunroof. Inspect the sunroof for proper alignment. Be sure the seals are secure.