LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1768 (Vibration Symptoms Diagnosis And Correction) >> Diagnostic Information and Procedures >> Vibration Analysis - Road Testing >> Test Description

Test Description

WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 4:  Obtaining rotational speed for the components rotating at tire/wheel speed is critical to systematically eliminating specific vehicle component groups. These component rotational speeds can be generated by using the J 38792-VS  , Vibrate Software, or through calculating them manually. See Special Tools .
  2. 9: 
    IMPORTANT: Be certain to OBSERVE for disturbances that match the customer's description FIRST, then look at the J 38792-A  frequency which corresponds with that disturbance. See Special Tools .
  3. 10:  Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed, before coasting down through the disturbance range.
  4. 11:  This test will either eliminate or confirm the engine as a contributing cause of the customer concern.
Vibration Analysis - Road Testing

Step Action Yes No
CAUTION: Refer to ROAD TEST CAUTION in Cautions and Notices.
1 Did you review the Diagnostic Starting Point - Vibration Diagnosis? Go to Step 2  Go to Diagnostic Starting Point - Vibration Diagnosis and Correction 
2 Visually inspect the tire and wheel assemblies, steering components and suspension components for any possible faults.
Are the tire and wheel assemblies, steering components and suspension components in good working condition?		 Go to Step 4  Go to Step 3 
3
IMPORTANT: Do NOT operate the vehicle until the faults are corrected.
Correct the faults with the tire and wheel assemblies, steering components, and/or the suspension components before proceeding.Did you correct the faults with the tire and wheel assemblies, steering components, and/or the suspension components?		 Go to Step 4  Go to Step 2 
4 
  1. Obtain the drive axle final drive ratio.
  2. If the J 38792-VS  , Vibrate Software, IS available, obtain the transmission gear ratios. See Special Tools .
  3. If the J 38792-VS  is NOT available, take note of the tire size on each axle, then calculate the tire rotational speed for each size tire used. See Special Tools . Refer to Component Rotational Speed Calculation .
Did you obtain the powertrain ratios for use with the J 38792-VS  , or calculate the component rotational speeds, if J 38792-VS  is NOT available?. See Special Tools .		 Go to Step 5  -
5
  1. Install a scan tool.
  2. With the scan tool, bring up the Powertrain Control Module data list and select Engine Speed.
Is the scan tool operating properly?		 Go to Step 6  Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
6 Using the J 38792-A  , Electronic Vibration Analyzer (EVA) 2 is the preferred method for gathering necessary vibration frequency data. See Special Tools .
If the J 38792-A  is not available, the necessary vibration frequency data will have to be obtained based on symptoms observed during testing. See Special Tools . Review Symptoms - Vibration Diagnosis and Correction  to become familiar with the possible frequency ranges. Review Symptoms - Vibration Diagnosis and Correction, as necessary throughout the remainder of diagnostics.
Is the J 38792-A  available for use? See Special Tools .		 Go to Step 7  Go to Step 8 
7 Install the J 38792-A  . See Special Tools .
Is the J 38792-A  operating properly? See Special Tools .		 Go to Step 8  Go to Electronic Vibration Analyzer (EVA) Description and Operation 
8 Did the customer concern indicate that the vibration occurs ONLY while the vehicle is standing still? Go to Vibration Analysis - Engine  Go to Step 9 
9 
  1. Install the J 38792-A  sensor, if available, to the component identified by the customer as most respondent to the vibration. See Special Tools . If no component was identified, install the J 38792-A  sensor, if available, to the steering column. See Special Tools . You may have to move the sensor to other locations later.
  2. Select a smooth, level road and slowly accelerate the vehicle up to highway speed.
  3. Observe the vehicle for disturbances that match the customer's description and note the following conditions:
    • The vehicle speed
    • The engine RPM
    • The transmission gear range and the specific gear
    • The vibration frequency reading, if detected by the J 38792-A  . See Special Tools .
    • The feel and/or sound of the disturbance
  4. If the vibration seems to excite a particular component of the vehicle more than the steering column, then move the J 38792-A  sensor, if available, onto that component and repeat steps 2 and 3. See Special Tools .
Were you able to duplicate the customer's concern?		 Go to Step 10  Go to Vibration Diagnostic Aids 
10 
  1. Accelerate the vehicle to a speed higher than the speed at which the disturbance occurs.
    2. IMPORTANT: If the vehicle is equipped with an automatic transmission, let the vehicle coast to a stop before shifting back into gear.
  2. Shift the vehicle into NEUTRAL and allow the vehicle to coast down through the disturbance range.
Does the disturbance still occur while coasting-down in NEUTRAL?		 Go to Step 12  Go to Step 11 
11 
  1. Select a smooth, level road and slowly accelerate the vehicle up to the speed at which the disturbance occurs.
  2. Decelerate and safely downshift by one gear range.
  3. Operate the vehicle at the same VEHICLE SPEED at which the disturbance occurs.
Does the same disturbance still occur while going the same vehicle speed in a lower gear range?		 Go to Vibration Analysis - Hub and/or Axle Input  Go to Vibration Analysis - Engine 
12 If the J 38792-A  is not available, refer to Symptoms - Vibration Diagnosis and Correction . See Special Tools .
Did the J 38792-A  detect a dominant frequency? See Special Tools .		 Go to Step 13  Go to Symptoms - Vibration Diagnosis and Correction 
13
  1. If the J 38792-VS  is available, use the drive axle final drive ratio, the specific transmission gear ratio, and the engine RPM to make a comparison to the dominant frequency reading recorded. See Special Tools .
  2. If the J 38792-VS  is NOT available, compare the dominant frequency reading recorded to the component rotational data which you calculated previously. See Special Tools .
Does the frequency data clearly fall within the tire/wheel parameters ONLY?		 Go to Vibration Analysis - Tire and Wheel  Go to Symptoms - Vibration Diagnosis and Correction 
scientia non olet · About LEMON Manuals