Engine-Driven Accessories

Engine-driven accessories that exhibit vibration pose some special challenges. For example, the drive belts may no longer be removed one at a time in order to isolate the condition. If removing the belt eliminates the vibration, reinstall the belt and operate each accessory one at a time in order to see which has the most effect on the vibration. However, one component may affect another because the Drive belt drives all of the accessories.
Inspect the accessory load to ensure that the load is not exciting the engine firing frequency.

Diagnosis
1. Compare the vibrations to a known good vehicle in order to ensure they are abnormal.
2. Remove the Drive belt.
3. If the vibration stops, perform the following steps:
1. Install the Drive belt.
2. Operate each accessory one at a time in order to see which has the most effect on the vibration.
4. Inspect for accessory load affecting the engine firing frequency.
5. Inspect the pulleys for misalignment or bends. Repair or replace as needed.
6. Inspect the A/C system for overcharging. Evacuate and recharge as needed. Refer to Refrigerant Recovery and Recharging in HVAC Systems with A/C - manual.
7. Inspect the engine oil level. Add or drain the oil as needed.

Diagnosis and Repair of Engine Firing Frequency-Related Vibrations
1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Follow the necessary safety precautions.
Refer to Work Stall Test Caution in Service Precautions.
3. Attempt to duplicate the vibration.
4. While the vibration is present, find the areas of the vehicle excited by the vibration.
5. Inspect for witness marks due to a rubbing component.
6. Isolate the component and re-evaluate the vibration.
7. Inspect for proper torque on the excited components. Tighten as needed.
8. If the vibration still exists, do a complete engine vibration diagnosis with the EVA.

Engine Vibration Diagnosis with the EVA




1. Place the EVA vibration sensor on the seat track rail with the UP label facing upward.
2. Plug the EVA into a 12 volt power supply.
3. Prepare the EVA for data recording:
1. Press RECORD.
2. Select a snapshot tag number.
3. Press ENTER in order to begin recording.
4. Slowly accelerate until the vibration occurs.
5. Remember the vehicle and the engine rpm where the disturbance occurs.
6. Press ENTER on the EVA in order to record the vibration data.
7. Perform the road test diagnoses in order to determine engine-speed or vehicle-speed sensitivity. Refer to Types of Road Test Procedures.