With so many "look alike" cars around in each price range, customer's loyalty depends on the faith in the quality of the car he or she has most recently bought. Air and water leaks, therefore, can be as disturbing to customers as mechanical defects.

Customers understand minor defects and are more likely to tolerate them. An air or water leak is different. It may take a long series of trial and error repairs to cure a troublesome leak. No wonder buyers lose faith in what otherwise may be fine vehicles.

That's why Ford Motor Co., Dearborn, MI, uses ultrasonic scanning to test its Crown Victoria and Grand Marquis models. In Ford's drive for quality, it uses the Ultraprobe 2000, an ultrasonic detector manufactured by UE Systems, Inc., Elmsford, NY, to find such leaks.

The Ultraprobe 2000 identifies air and water leaks and wind noise sources. The device is easy to use, compact, and lightweight. It changes ultrasound frequencies to frequencies that a person can hear. Thus, the operator "hears" ultrasound through the earphones supplied with it, and gages the sound intensity by deflections on a meter.

Airborne ultrasound can be detected because of the nature of ultrasound. Audible sound waves penetrate walls and reflect off other surfaces, making it difficult to trace their sources. Ultrasound cannot penetrate solids but can pass through the smallest gaps in gaskets or weld seams.

An ultrasonic test is simple. It requires only two parts: an ultrasonic scanner receiver, such as the Ultraprobe 2000, and an ultrasonic warble tone generator. To test a gasket around a car window or door, for example, the warble tone generator is placed inside a vehicle. It floods the car's interior with ultrasound. Then, with the windows and doors closed, the operator scans the outside using the ultrasonic receiver and pinpointing leak sources.

Ford, as part of its qualified vehicle modifier program, has tried to help limousine manufacturers achieve consistently high quality. This program has raised limousine quality to a level that satisfies Ford. The company continues to seek ways of going further, however.

According to Roy Radikovich, Ford's vehicle development manager, luxury vehicles, Ford adopted ultrasonic evaluation to detect:

• Wind noises and other disturbing sounds that enter passenger compartment.

• Water leaks not non-nally found by limousine manufacturers in normal water spray tests. Such leaks usually mean higher warranty costs for manufacturers.

Limousine manufacturers saw how to find potential leaks they might not otherwise detect. A water leak behind a trim panel, for example, probably remains concealed until a good deal of damage is done. The program points out that ultrasonic equipment quickly and easily can find poorly sealed areas, assuring they would not lead to warranty claims.

To be competitive, the two best-in-class vehicles had to achieve best-in-class performance. This meant that passengers in normal seated positions would detect no leaks at all. Such leaks are now pinpointed on glass runs, and designs have been improved to achieve best-in-class performance. Ford developed methods for a better understanding of wind noise and water leaks during the vehicles' launch cycles.

Three or four years ago, Joe Mark, a Ford vehicle development engineer, was investigating a leak problem during the evaluation of the Crown Victoria and Grand Marquis prototypes. "We wanted a graphical representation of this problem to illustrate at meetings and seminars to focus attention on it, and explore solutions," says Mark. "We had to devise new methods. We investigated using ultrasound for leak detection and have since found it very useful."

For in-plant use, the instrument is calibrated  for full signal strength. In road tests, leak evaluation depends on a subjective 1-2-3-scale system that is later correlated with the ultrasonic detector's heterodyne signal.

To assure consistency, Mark uses the same operator for all car-to-car comparisons. This ensures a consistent approach in such matters as the probe's angle and the cone's distance from the measured surface.

Mark has found this technique especially useful when working with Ford's suppliers. Ultrasonic scanning has enabled him to improve the overall quality of subsystems such as door, body, and cut line seats. One of the main uses of ultrasonic detection at Ford is in detecting aspirant windshield leaks, a major source of customer dissatisfaction. In the past, a stethoscope detected these leaks. This method is highly subjective and difficult to document, however.

"The Ultraprobe allows us to correlate subjective and quantified data. These data enable us to formulate solutions to some of our problems," says Mark.