GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 General Information 🢒 Vibration Diagnosis and Correction 🢒 Vibration Analysis - Engine/Accessory Isolation

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A loose, damaged, misaligned, or defective powertrain insulator and/or bracket may cause a vibration transfer path into the passenger compartment.

    2.

  2. A loose, damaged, misaligned, or defective exhaust system insulator and/or bracket may cause a vibration transfer path into the passenger compartment.

    3.

  3. Incorrectly seated and/or aligned powertrain components and/or exhaust components may cause a vibration transfer path into the passenger compartment.

    Observe the following items when loosening powertrain support to re-bed the system:

    Do not loosen the mount bracket to engine bolts/nuts; do not loosen the mount bracket-to-vehicle frame bolts/nuts if the mount brackets are used.

    Loosen the mount to mount bracket bolts/nuts if mount brackets are used, or loosen the mount to slotted holes in vehicle frame bolts/nuts if a direct-mount design is used.

    4.

  4. Non-rotating engine driven accessory component systems can no longer produce a unique disturbance.

    5.

  5. Non-rotating engine driven accessory components can no longer produce a unique disturbance. If a disturbance is still present, but the characteristics have been altered, it is possible that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance.

    If a disturbance is still present, but the characteristics have NOT been altered, it is NOT likely that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance.

    6.

  6. If the mark placed on the face of an engine driven accessory pulley seems to stand still while performing this test, which indicates that accessory system is either responding to an existing frequency, such as engine firing pulses, or creating a disturbance.

    7.

  7. A loose, damaged, misaligned, or defective engine driven accessory system insulator and/or bracket may cause a transfer path into the passenger compartment.

    8.

  8. Removing the engine driven accessory and bracket allows a thorough inspection to determine if any conditions are present that may create a transfer path into the passenger compartment.

Step

Operation

Yes

No

Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

   • When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:
      - Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.
      - If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.
      - All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.
      - When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.
   • When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:
      - Support the suspension at normal ride height.
      - Do not apply the brake with the brake rotors removed.
      - Do not place the transmission in PARK with the drive axles spinning.
      - Turn Off the ignition in order to stop the powertrain components from spinning.
   • When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

 

1

Have you sent here from the Vibration Analysis - Engine?

Go to Step 2

Go to Vibration Analysis - Engine

2
  1. Using the engine RPM and frequency data recorded for the customer's vehicle, determine the order of engine rotation to which the disturbance is related.
  2. Determine the causes of the disturbance relating to a specific order of engine rotation.

Refer to Engine Order Classification .

Does the Engine Order Classification table indicate that the disturbance order is the same as the engine firing frequency?

Go to Step 4

Go to Step 3

3

Does the Engine Order Classification table indicate that the disturbance is likely related with engine driven accessories?

Go to Step 9

Go to Step 4

4

Inspect the Powertrain Support for the following conditions:

    • Loose and/or missing fasteners
    • Improper alignment
    • Cracked, dry-rotted, and/or oil-soaked insulators
    • Twisted, broken, torn, and/or collapsed insulators
    • Bent, twisted, and/or deformed brackets

Does the powertrain mounts exhibit the above conditions?

Go to Step 5

Go to Step 6

5

Replace the powertrain mounts as necessary. Refer to the following procedures:

Have you finished the replacement?

Go to Step 15

--

6

Inspect the exhaust system components for the following conditions:

    • Loose and/or missing fasteners
       - Heat Shields
       - Joints and/or couplings:
       - Nuts, bolts, studs, clamps, straps
       - Bracket and/or insulator mounting
    • Inadequate clearance to body and/or chassis components.
        Inspect the above clearance with the exhaust system both COLD and HOT and in NEUTRAL, FORWARD and REVERSE gears
    • Improper alignment
    • Disconnected and/or missing insulators
    • Cracked, dry-rotted, and/or oil-soaked insulators
    • Stretched, broken, torn, and/or collapsed insulators
    • Bent, twisted, cracked, and/or deformed brackets

Does any of these exhaust components exhibit the conditions?

Go to Step 7

Go to Step 8

7

Repair, replace, and/or realign exhaust system components as necessary.

Have you finished repair, replaced and/or realignment?

Go to Step 15

--

8

Reset powertrain:

  1. Loosen but not remove all powertrain supports and exhaust system hangers.
  2. Ensure that the exhaust equipped with flexible coupling moves flexibly.
  3. Start the engine.
  4. Settle the powertrain by shifting the transmission from DRIVE to REVERSE.
  5. Place the transmission into NEUTRAL.
  6. Turn OFF the ignition.
  7. Tighten all loosened fasteners with the powertrain in a relaxed position. Refer to the following procedures:
    8. •  Transmission Mount Inspectionfor the 5L50-E transmission

Have you completed the operation?

Go to Step 15

--

9

Notice: Do not run the engine for longer than 60 seconds with the accessory drive belt, or belts removed, or overheating and/or damage may result.

  1. Remove the engine accessory drive belt.
  2. Block the front wheels.
  3. Apply BOTH the service brake and park brake.
  4. With the scan tool installed, start the engine.
  5. Place the transmission in NEUTRAL or PARK.
  6. Increase the engine RPM to the level recorded during duplication of the disturbance.
  7. Allow the engine to idle, then place the transmission in DRIVE.
  8. Increase the engine RPM to the level recorded during duplication of the disturbance.
  9. Turn OFF the ignition.
  10. Install the engine accessory drive belt.

Does the disturbance significantly reduce or eliminate?

Go to Step 11

Go to Step 10

10

Are the disturbance characteristics altered but still present?

Go to Step 12

Go to Step 17

11

  1. Mark the suspected accessory pulleys, including any related idler pulleys, near the outer edge with a paint mark.
  2. Install the Inductive Pickup Timing Light J 38792-25 to the J 38792-A (EVA).
  3. Refer to Electronic Vibration Analyzer (EVA) Description and Operation for the information on Electronic Vibration Analyzer (EVA) feature.
  4. Block the front wheels.
  5. Apply BOTH the service brake and park brake.
  6. Start the engine, with the scan tool and J 38792-A still installed .
  7. Select the Smart Strobe feature on the J 38792-A .
  8. Enter the recorded frequency of the disturbance as the initial frequency for strobe operation.
  9. Have an assistant place the transmission in NEUTRAL or PARK.
  10. Slowly increase the engine RPM to the level recorded during duplication of the disturbance and then maintain that speed.
  11. Check each suspected accessory pulleys with J 38792-25 to determine if any of them is related with the distance frequency.
  12. Check each accessory system under both engaged and maximum load and disengaged or under minimum load conditions.
  13. Allow the engine to idle, then place the transmission in DRIVE.
  14. Slowly increase the engine RPM to the level recorded during duplication of the disturbance and then maintain that speed.
  15. Check each suspected accessory pulleys with J 38792-25 to determine if any of them is related with the disturbance frequency.
  16. Check each accessory system under both engaged and maximum load and disengaged or under minimum load conditions.
  17. Turn OFF the ignition.

Have you determined that the engine accessory system is related with disturbance frequency?

Go to Step 12

Go to Vibration Diagnostic Aids

12

Inspect the engine driven accessory system component for the following conditions:

    • Loose and/or missing fasteners
       - Heat Shields (if equipped)
       - Joints and/or couplings:
       - Nuts, bolts, studs, clamps, straps
       - Bracket and/or insulator mounting
    • Inadequate clearance to body and/or chassis components
        Inspect accessory system both under a LOAD and UNLOAD conditions.
    • Improper alignment
    • Bent or damaged pulleys
    • Disconnected and/or missing insulators
    • Cracked, dry-rotted, and/or oil-soaked insulators
    • Stretched , broken, torn, and/or collapsed insulators
    • Bent, twisted, cracked and/or deformed brackets

Does any of the engine driven accessory system components exhibit the above conditions?

Go to Step 14

Go to Step 13

13

  1. Remove the engine driven accessory and bracket from engine.
  2. Thoroughly inspect the accessory bracket, bolts/nuts/studs, and the accessory itself for the following conditions:
  3. Bent, twisted, cracked and/or deformed conditions.
  4. Replace any of the components found to exhibit any of these conditions.
  5. Reinstall the components to the engine

Did you find and correct the condition?

Go to Step 15

Go to Step 18

14

Repair, replace, and/or realign the engine driven accessory system components as necessary.

Have you finished the repair, replacement, and/or realignment?

Go to Step 15

--

15

Retest the vehicle to determine if the disturbance is now significantly reduced or eliminated. Perform the following steps:

  1. Install the scan tool into the customer's vehicle.
  2. Install the J 38792-A into the customer's vehicle. Place the sensor at exactly the same location as the vehicle previously located for test.
  3. Block the front wheels.
  4. Apply BOTH the service brake and the park brake.
  5. Start the engine.
  6. Place the transmission in NEUTRAL or PARK.
  7. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  8. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .
  9. Place the transmission in DRIVE.
  10. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  11. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .
  12. If the disturbance has been significantly reduced or eliminated, confirm the results after placing the transmission into REVERSE and then repeat steps 10 and 11.

Does the disturbance significantly reduced or eliminated?

Go to Step 19

Go to Step 16

16

Have you investigated the powertrain as a possible cause of the disturbance?

Go to Step 17

Go to Step 4

17

Have you investigated the engine driven accessories as a possible cause of the disturbance?

Go to Vibration Analysis - Engine Balance

Go to Step 9

18

Replace the engine driven accessory components causing the disturbance.

Have you finished the replacement?

Go to Step 19

--

19
  1. Install or connect all components that were removed or disconnected during diagnosis.
  2. Perform the Vibration - Road Testing table. Refer to Vibration Analysis - Road Testing .

Is the disturbance still present?

Go to Step 2

System OK