Component Tests
Component TestsIdle Air Control (IAC) Valve
1. Open the hood.
Note:
^ Key symptom is elevated idle speed while noise is occurring.
Note:
^ Snapping" the throttle can induce the noise.
2 Verify the condition by operating the vehicle for a short time.
3. Inspect the IAC. If physical evidence of contamination exists, install a new IAC.
4. While the noise is occurring, either place an EngineEAR near the IAC valve and the inlet tube, or create a 6.35 mm (0.25 inch) - 12.7 mm (0.50 inch) air gap between the inlet tube and the clean air tube. If the IAC valve is making the noise, install a new IAC valve.
5. Test the vehicle for normal operation.
Steering Gear Grunt/Shudder Test
1. Start and run the vehicle to operating temperature.
2. Set engine idle speed to 1,200 rpm
Caution:
^ Do not hold the steering wheel against the stops for more than three to five seconds at a time. Damage to the power steering pump will occur.
3. Rotate the steering wheel to the RH stop, then turn the steering wheel 90 degrees back from that position. Turn the steering wheel slowly in a 15 to 30 degree arc.
4. Turn the steering wheel another 90 degrees. Turn the steering wheel slowly in a 15 to 30 degree arc.
5. Repeat the test with power steering fluid at different temperatures.
6. If a fight grunt is heard or a low (50-200 Hz) shudder is present, this is a normal steering system condition
7. If a loud grunt is heard or a strong shudder is felt, fill and purge the power steering system.
Checking Tooth Contact Pattern and Condition of the Ring and Pinion
There are two basic types of conditions that will produce ring and pinion noise. The first type is a howl or chuckle produced by broken, cracked, chipped, scored or forcibly damaged gear teeth and is usually quite audible over the entire speed range. The second type of ring and pinion noise pertains to the mesh pattern of the gear pattern. This gear noise can be recognized as it produces a cycling pitch or whine. Ring and pinion noise tends to peak in a narrow speed range or ranges, and will tend to remain constant in pitch.
1. Raise and support the vehicle.
2. Remove the differential housing cover.
3. Inspect the gear set for scoring or damage.
4. In the following steps, the movement of the contact pattern along the length is indicated as toward the "heel" or "toe" of the differential ring gear.
5. Apply a marking compound to a third of the gear teeth on the differential ring gear. Rotate the differential ring gear several complete turns in both directions until a good, clear tooth pattern is obtained. Inspect the contact patterns on the ring gear teeth.
6. A good contact pattern should be centered on the tooth. It can also be slightly toward the toe. There should always be some clearance between the contact pattern and the top of the tooth.
^ Tooth contact pattern shown on the drive side of the gear teeth.
7. A high, thick contact pattern that is worn more toward the toe.
^ Tooth contact pattern shown on the drive side of the gear teeth.
^ The high contact pattern indicates that the drive pinion is not installed deep enough into the carrier.
^ The differential ring gear backlash is correct, a thinner drive pinion shim is needed. A decrease will move the drive pinion toward the differential ring gear.
8. A high, thin contact pattern that is worn toward the toe.
^ Tooth contact pattern shown on the drive side of the gear teeth.
^ The drive pinion depth is correct. Increase the differential ring gear backlash.
9. A contact pattern that is worn in the center of the differential ring gear tooth toward the heel.
^ Tooth contact pattern shown on the drive side of the gear teeth.
^ The low contact pattern indicates that the drive pinion is installed too deep into the carrier.
^ The differential ring gear backlash is correct. A thicker drive pinion shim is needed.
10. A contact pattern that is worn at the top of the differential ring gear tooth toward the heel.
^ Tooth contact pattern shown on the drive side of the gear teeth.
^ The pinion gear depth is correct. Decrease the differential ring gear backlash.
Tire Wear Patterns and Frequency Calculations
Tire Wear Chart
Wheel and tire NVH concerns are directly related to vehicle speed and are not generally affected by acceleration, coasting or decelerating. Also, out-of-balance wheel and tires can vibrate at more than one speed. A vibration that is affected by the engine rpm, or is eliminated by placing the transaxle in NEUTRAL is not related to the tire and wheel. As a general rule, tire and wheel vibrations felt in the steering wheel are related to the front tire and wheel assemblies. Vibrations felt in the seat or floor are related to the rear tire and wheel assemblies. This can initially isolate a concern to the front or rear. Careful attention must be paid to the tire and wheels. There are several symptoms that can be caused by damaged or worn tire and wheels. Carry out a careful visual inspection of the tires and wheel assemblies. Spin the tires slowly and watch for signs of lateral or radial runout. Refer to the tire wear chart to determine the tire wear conditions and actions.
For a vibration concern, use the vehicle speed to determine tire/wheel frequency and rpm. Calculate tire and wheel rpm the frequency by carrying out the following:
^ Measure the diameter of the tire.
^ Record the speed at which the vibration occurs.
^ Obtain the corresponding tire and wheel rpm and frequency from the Tire Speed and Frequency Chart.
- If the vehicle speed is not listed, divide the vehicle speed at which the vibration occurs by 16 (km/h (10 mph). Multiply that number by 16 km/h (10 mph) tire rpm listed for that tire diameter in the chart. Then divide that number by 60. For example: a 40 mph vibration with 835 mm (33 inch) tires. 40 - 10 = 4. Multiply 4 by 105 = 420 rpm. Divide 420 rpm by 60 seconds = 7 Hz at 40 mph.
Tire Speed and Frequency Chart