Engine Related Vibration

Engine vibration is usually due to one or more of the following conditions:
- First-order engine imbalance
- Inherent engine firing sequence
- Inherent shaking engine forces
- Engine-driven accessories
Because these vibrations are engine-speed related, they are also normally torque sensitive. These vibrations may appear and disappear at different vehicle or road speeds, but will always appear at the same engine speed.
For example, if a customer states that a vibration is present at 40 Kph (25 mph), 64 Kph (40 mph), and again at 104 km/h (65 mph), and that the symptoms of the vibration are similar at all of these speeds, the vibration is probably engine-speed related. Any disturbance or vibration that is present during the following road tests would be considered engine-speed related:
- The Neutral run-up test
- The downshift test
- The brake torque test
Any vibration that is present during the Neutral coast-down test is not engine-speed related. The engine-related vibrations covered in this diagnosis are engine-speed sensitive only.