Engine Related Vibration. Chevrolet Metro 2000

For 1990-2009 cars

Usually, engine vibration is caused by one or more of the following conditions:

• | First-order engine imbalance

• | The inherent engine firing sequence

• | Inherent shaking engine forces

• | Engine-driven accessories

Because these vibrations are related to the engine speed, the vibrations are also torque-sensitive. These vibrations may appear and disappear at different vehicle speeds or different road speeds, but will always appear at the same engine speed.

For example, the vibration is probably related to the engine speed if the following conditions exist:

• | The customer states that a vibration is present at 40 km/h (25 mph), 64 km/h (40 mph), and again at 104 km/h (65 mph).

• | The symptoms of the vibration are similar at all of these speeds.

Any disturbance or vibration that occurs during the following road tests would be related to the engine speed:

• | 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 related to the engine speed. The engine-related vibrations that are discussed in this diagnosis are sensitive only to the engine speed.

### First-Order Engine Imbalance

Notice: Do not accelerate against the brakes for longer than 10 seconds. Do not overheat the engine or the transmission. Depending on the vehicle design, the engine will only accelerate to a certain point under these conditions. Also, care should be taken during diagnosis as some disturbances may be created during brake torque that normally do not exist.

Notice: Proper flywheel installation requires carefully WALKING the flywheel onto the crankshaft and stagger-tightening the bolts. Proper torque converter to flywheel installation then requires gradually WALKING the torque converter to be flush with the flywheel, prior to installing the bolts. Do not draw the torque converter to the flywheel with the bolts. If these precautions are not followed, warping or bending of the flywheel and/or damage to the transmission torque converter may result.

Engine imbalance is a condition that exists when a component that rotates at crankshaft speed is either unbalanced or has excessive runout. In rare cases, the crankshaft may be unbalanced. Balancing the component or correcting the runout may bring the disturbance to an acceptable level.

#### Symptoms

• | Vehicles shake at low speeds of 500-1,200 rpm, or 8-20 Hz

• | Roughness and BOOM at higher speeds of 1,200-3,000 rpm, or of 20-50 Hz

• | Vibration, which is usually detected during the Neutral run-up test

### Isolating the Components

1. Perform the Neutral run-up test. Note the RPM at which the vibration is the worst and the most severe. Refer to Types of Road Test .
2. Inspect all powertrain mounts. Repair or replace the mounts, as necessary
3. Inspect for any bindings or for any ground-outs in the exhaust system.

Important: Steps 4-17 apply only to vehicles equipped with automatic transmission.

4. Mark the location of the torque converter to the flywheel.
5. Disconnect the torque converter from the propeller shaft, pushing the converter back from the flywheel.
6. Tie up the converter, away from the flywheel.
7. Perform the Neutral run-up test again. Refer to Types of Road Test . Observe the flywheel.

• | If the flywheel shows any wobble or any lateral runout, replace the flywheel. For a 1.0L engine, refer to Engine Flywheel Replacement in Engine Mechanical. For a 1.3L engine, refer to Engine Flywheel Replacement in Engine Mechanical.

• | Index the torque converter in 3 different positions. If the disturbance still exists, replace the torque converter. Refer to Transmission Replacement in Automatic Transmission.

8. If the vibration still exists, inspect the harmonic balancer.
9. If the vibration still exists, the problem is related to residual engine imbalance. Refer to Correcting Residual Engine Imbalance below.

### Correcting Residual Engine Imbalance

1. Install the washers on the harmonic balancer pulley bolts.
2. Replace the bolts with longer bolts of equal hardness, as necessary.
3. Install the J-nuts on the outer edge of the circular holes in the flywheel.
4. For M/T only, inspect the flywheel and the pressure plate for the following conditions:

• | Correct factory indexing

• | The white paint spot on the flywheel and on the pressure plate should line up.

• | Warping

• | Balance

### Engine Firing Frequency

Firing frequency is the term that describes the pulses that are created while the engine fires each cylinder. All engines have a firing frequency, but it is necessary to prevent these disturbances from entering the passenger compartment. First, inspect for the following conditions:

• | The engine and the exhaust system are mounted in a relaxed position.

• | All of the mounts and of the hangers are in good condition and are correct for the application.

• | None of the components, the hoses, or the lines are grounding to the frame or to the body.

Important: The frequency of these disturbances will depend on the number of cylinders. The engine order will always be equal to one-half the number of cylinders. This is because a four-stroke engine requires 2 complete revolutions of the crankshaft in order to fire all of the cylinders.

For example, a V8 engine will fire cylinders 1, 3, 5, and 7 on the first revolution. Cylinders 2, 4, 6, and 8 will fire on the second revolution. This causes 4 firing pulses per revolution of the crankshaft. This is called fourth order.

#### Engine Firing Frequencies

Condition | Engine Speed (RPM) | Any Engine First Order (Hz) | 4-Cylinder Second Order (Hz) | 6-Cylinder Third Order (Hz) | 8-Cylinder Fourth Order (Hz)
--- | --- | --- | --- | --- | ---
Shake | 500 750 1000 1500 | 8.3 12.5 16.6 25 | 16.6 25 33.3 50 | 24.9 37.5 49.8 75 | 33.2 50 66.4 100
Roughness | 2000 2500 | 33.3 41.6 | 66.6 83.2 | 99.9 124.8 | 133.2 166.4
Buzz | 3000 3500 4000 | 50 58.3 66.6 | 100 110.6 132.4 | 150 174.9 199.8 | 200 233.2 266.4

### Engine Firing Frequency Symptoms

The following are symptoms of engine firing frequency:

• | The vibration may be torque sensitive.

• | The vibration is related to the engine speed.

• | The vibration is heard as a boom or a moan.

• | The vibration is felt as a shake, as a roughness, or as a buzz. The type of vibration depends on the number of cylinders.

• | The vibration excites the resonance of a system or of a component. This causes the system or the component to have a narrow RPM range.

The key to correcting these types of complaints is to isolate the vibration from the passenger compartment or from the body.

### Engine Firing Frequency-Related Vibration Causing Components

1. Inspect for collapsed engine mounts. Replace the mounts as necessary

Refer to Engine Mount Replacement in Engine Mechanical.

2. Inspect the exhaust hangers.

Exhaust systems can expand 2.5-5 cm (1-2 in) when the systems are hot.

2.1. | Remove the hangers one at a time.

2.2. | Adjust or replace the hangers as necessary.

3. Lubricate the manifold flexible coupling, if applicable.
4. Inspect the A/C lines and the PS lines.

4.1. | Isolate the hoses from the body.

4.2. | Install the retainers.

5. Inspect the drive belt for whipping.
6. Inspect the accessory unit fasteners for damage or for looseness.
7. Inspect the body panels for missing welds or for loose welds.
8. Remove any aftermarket equipment that may complete a transfer path into the passenger compartment.
9. Inspect the exhaust system and the powertrain mounts.

If necessary, use the following steps in order to bed the engine and align the exhaust system:

9.1. | Loosen the mounts and the hangers.

9.2. | Settle the powertrain by shifting from DRIVE to REVERSE.

9.3. | Tighten all fasteners with the powertrain in the relaxed position.

Some residual vibrations may be normal. Compare the vibrations with a similar vehicle in order to get a feel for what is commercially acceptable, preferably with the customer present. Refer to bulletins for updates on the use of mass damper weights for specific applications.

### Inherent Engine Shaking Forces

#### Engine Order Vibration

Engine Order | L3 | L4 (without Balance Shaft) | L4 (with Balance Shaft) | L6 | V6 60° & V6 90° (with Balance Shaft) | V6 90° (without Balance Shaft) | V8 90°
--- | --- | --- | --- | --- | --- | --- | ---
½ Order Torque Sensitive | Single Cylinder Misfire | Single Cylinder Misfire | Single Cylinder Misfire | Single Cylinder Misfire | Single Cylinder Misfire EGR/Fuel Variance | Single Cylinder Misfire EGR/Fuel Variance | Single Cylinder Misfire
1st Order Imbalance | Normal | Abnormal | Abnormal | Abnormal | Abnormal | Normal | Abnormal
1.5 Order Torque Sensitive | Normal | -- | -- | -- | Bank-to-Bank EGR/Fuel Variance | Bank-to-Bank EGR/Fuel Variance | --
2nd Order | Normal | Normal | Abnormal | Abnormal | Normal | Normal | Abnormal
2nd Order Torque Sensitive | -- | Normal | Normal | -- | -- | -- | Bank-to-Bank EGR/Fuel Variance
3rd Order Torque Sensitive | Normal (Small Amount) | -- | -- | Normal | Normal | Normal | --
4th Order Torque Sensitive | -- | Normal (Small Amount) | Normal (Small Amount) | -- | -- | -- | Normal

Just like firing frequency, some engine disturbances are the result of normal operation. Some engines can have additional inherent vibration because of the following elements:

• | The cylinder arrangement

• | The design

• | The firing order

Before attempting to repair a disturbance, compare the disturbance to another known good vehicle. Although some vibrations could be normal, the vibrations may not be pleasant to the customer.

Isolate the vibration from the passenger compartment in order to resolve an inherent engine disturbance. Follow the same procedure that is outlined for vibrations that are related to the engine firing frequency. Refer to Engine Firing Frequency-Related Vibration Causing Components.

### Engine-Driven Accessories

Engine-driven accessories that exhibit vibration present some special challenges. For example, you cannot remove the drive belts 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. This will determine which of the accessories has the greatest effect on the vibration. However, one component may affect another component, because the drive belt drives all of the accessories. Inspect the accessory load in order to confirm that the load is not exciting the engine firing frequency.

#### Diagnosis

1. Compare the vibrations to a known good vehicle in order to confirm that the vibrations are abnormal.
2. Remove the drive belt.
3. If the vibration stops, perform the following steps:

3.1. | Install the drive belt.

3.2. | Operate each accessory one at a time in order to see which accessory has the greatest effect on the vibration.

4. Inspect for an accessory load that is affecting the engine firing frequency.
5. Inspect the pulleys for misalignment or for bends. Repair or replace the pulleys as necessary.
6. Inspect the A/C system for overcharging. Evacuate and recharge the A/C system as necessary. Refer to Refrigerant Recovery and Recharging in HVAC System with A/C Manual.
7. Inspect the engine oil level. Add or drain the oil as necessary.

### 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.

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.

2. Follow the necessary safety precautions.
3. Try to duplicate the vibration.
4. While the vibration is present, find the areas of the vehicle that are excited by the vibration.
5. Inspect for witness marks that were made by a rubbing component.
6. Isolate the component, and reevaluate the vibration.
7. Inspect for correct torque on the excited components. Tighten as necessary.
8. If the vibration still exists, refer to 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:

3.1. | Press RECORD.

3.2. | Select a snapshot tag number.

3.3. | Press ENTER in order to begin recording.

4. Slowly accelerate until the vibration occurs.
5. Remember the vehicle RPM 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 sensitivity or vehicle-speed sensitivity. Refer to Types of Road Test .