1. Convert the engine speed in revolutions per minute (RPM), recorded during duplication of disturbance into Hertz (RPS), by dividing the RPM by 60 seconds. Refer to the following example:

1,200 RPM divided by 60 = 20 Hz (or RPS)

2. Compare the dominant frequency (HZ) recorded during duplication of the disturbance with the engine speed just converted into Hz, to determine if they are related.
3. If the dominant frequency (Hz) recorded during duplication of the disturbance and the engine speed converted into Hz, are related, then this vibration is related with an engine FIRST ORDER rotation frequency. The engine first order disturbances are usually related with an imbalanced component. Refer to Engine Order Related Disturbances table.
4. If the dominant frequency (Hz) recorded during duplication of the disturbance and the engine speed converted into Hz are NOT related, then determine if this vibration is related with an engine's firing frequency. Refer to Engine Firing Frequency Classification.

Engine firing frequency is a term used to describe the number of firing pulses (one firing pulse = one cylinder firing) that occur during ONE complete revolution of the crankshaft, multiplied by the number of crankshaft RPS (Hz).

1. Calculate the engine firing frequency.

•	To determine the firing frequency of a 4-stroke engine during ONE complete revolution of the crankshaft, multiply the engine speed (Hz) by HALF of the total number of cylinders in the engine.

•	For example: The engine speed, converted into Hz, 20 Hz; if the vehicle was equipped with a V8 engine, then 4 of the 8 cylinders would actually fire during ONE complete revolution of the crankshaft.

-	Multiply the converted engine speed (20 Hz) by 4 firing cylinders.

-	20 Hz X 4 = 80 Hz

-	The engine firing frequency, if the engine runs at the original speed of (1,200 RPM) recorded during duplication of the disturbance, would be 80 Hz.

-	Similarly, a 6-cylinder engine would have a firing frequency of 60 Hz at the same speed of (1,200 RPM).

-	20 Hz X 3 = 60 Hz

2. Compare the dominant frequency (Hz) recorded during duplication of the disturbance with the engine firing frequency (Hz) just calculated to determine if they are related.
3. If the dominant frequency (Hz) recorded during duplication of the disturbance and the engine firing frequency (Hz), just calculated, are related, then this disturbance is related with the engine FIRING FREQUENCY. Engine firing frequency disturbances are usually related with improper component isolation. Refer to Engine Order Related Disturbances table.
4. If the dominant frequency (Hz) recorded during duplication of the disturbance and the engine firing frequency (Hz), just calculated, are NOT related, then determine if this disturbance is related to another engine order classification. Go to Other Engine Order Classification.

1. Multiply the engine speed (converted into Hz) recorded during duplication of the disturbance by different possible order-numbers, other than 1 (first order) or the number used to determine engine firing frequency.
2. Compare the dominant frequency (Hz) recorded during duplication of the disturbance with the other possible engine orders just calculated, to determine if they are related.
3. If the dominant frequency (Hz), recorded during duplication of the disturbance and one of the other engine order frequencies (Hz) are related, then an engine related disturbance of that order is present. If an engine related disturbance is present that is NOT related to first order or firing frequency (Hz), then it could be related to an engine driven accessory system. Go to Engine Driven Accessories Related to Engine Order.

Engine driven accessory systems can be related to specific engine orders depending upon the relationship of the accessory pulley diameter and the crankshaft pulley diameter. For example:

Improper isolation that causes a transfer path into the passenger compartment or to another major component of the vehicle body, which causes engine driven accessories that contributed to, excited by or became the sole cause of disturbance.

Using the J 38792-VS , Vibrate Software, accurately measuring the diameters of the accessory pulleys and the crankshaft pulley, and performing the appropriate diagnostic procedures completely, this will determine the specific accessory system which is either contributing to or causing the customer's concern.