A running engine always vibrates slightly, but the amplitude depends on the design of the unit. A slight tremor felt on the steering wheel or the control lever of the box in idle mode is the norm. But if the engine vibration at idle speed is transmitted to the body and is well felt by the driver, it is necessary to check the transmission.
About the essence of the phenomenon
When the engine is running, the translational motion of the pistons is converted into rotational motion of the crankshaft, which creates forces of inertia – sources of vibration. The inertia of the pistons of the crank mechanism tends to lift or press the crankshaft into the supports. This negative effect can be overcome by increasing the number of cylinders or installing balancer shafts.
Vibrations are transmitted to the body, so rubber or hydraulic supports are used to dampen engine vibrations.
As a result, the level of comfort is increased, and the driver and passengers feel only a slight shudder when driving. But unpleasant and strong engine vibration at idle, which is transmitted to the body, always indicates a malfunction of the power unit or related components.
Vibration of the engine at idle and low speeds: causes, signs, diagnosis
Unpleasant vibration in the cabin at idle speed is transmitted from the engine and is its consequence:
- breakdown of the ignition or fuel supply systems;
- incorrect attachment of the power unit to the body;
- incorrect selection of timing;
- incorrect selection of piston group parts during repair;
- and a number of other factors (e.g., damaged rims or unbalanced wheels).
Engine Tremor
When the ignition fails (trojan), the vehicle jerks at idle and the jolts are transmitted to the body. In addition, the engine poorly enters the operating mode, stalls when the gas is dropped.
There may be several reasons – a non-working candle, a heated valve or piston, excessive gasoline supply by the injector. The method of troubleshooting depends on the engine design. On motors with fuel injection, part of the defects can be determined with the help of computer diagnostics.
Looseness of the fastening of the internal combustion engine
When assembled at the factory, the bolts fixing the engine to the lining and body parts are tightened with a torque wrench and marked. In unskilled repairs, the tightening torques are not always observed. As a result of temperature fluctuations and vibration, bolts or nuts will loosen spontaneously.
If the owner notices that the engine shakes after the repair, which was accompanied by the removal of supports, then it is necessary to check the tightening of the fastening of parts to the units and the body.
Malfunction of the engine support pads
The engine and gearbox are mounted on supports that are attached to the body components and subframe (floating mounting point), providing vibration damping while maintaining a small movement of the powertrain.
Tears in the rubber gaskets on the subframe or spars, as well as fluid leaks from the hydraulic mounts, affect the normal position of the engine. Vibrations occurring at idle or knocks during gear shifting or sudden acceleration are transmitted to the vehicle body.
Fuel system malfunction
A common cause of vibrations transmitted to the body when the engine is idling is fuel supply or ignition problems.
Ignition misses cause uneven engine operation and a drop in crankshaft speed, as well as vibration.
Ignition problems
Improper spark formation causes the idling engine to vibrate, which is then transmitted to the body. Injector engines record the problem as an error with the Check Engine light on at the same time.
Carburetor engines are not equipped with a diagnostic system, since you can find a faulty plug by alternately disconnecting the wires. When disconnecting a serviceable plug, vibration increases and the engine may stall.
Fuel system contamination
A drop in fuel pressure leads to uneven operation of injectors and vibration, which is transmitted to the body. At the same time, the engine does not rev up well and may stall spontaneously.
Clogged carburetor jets can also cause vibration or uneven engine operation.
Fuel injector problems
Vibration of an engine with a distributed injection system or direct gasoline supply to the cylinders occurs when the injector malfunctions and then transmits to the body. Shuddering will be observed at idle and when the rpm rises. A Check Engine warning light may illuminate on the dashboard.
Cylinder-Piston Group Imbalance
The engine will “shake” at idle if the lower part of the piston has burned through. In addition to a small change in the weight of the reciprocating parts, there is deactivation of the cylinders due to loss of compression. There are no other causes that can cause imbalance of the crankshaft and piston group.
When overhauling an engine, the weight of the connecting rod and piston must be the same for all cylinders (the tolerance field is determined by the engine design).
If the weight distribution is disturbed, vibration occurs and is transmitted to the body. This phenomenon will be observed at idle and at higher rpm. Body or engine shaking can also occur when the crankshaft is misaligned (e.g., due to improper grinding of the journals during repair).
Timing belt and camshaft pulleys
A common cause of vibration of the power unit at idle is incorrect adjustment of the timing when replacing the belt. A small shift of the shafts relative to the marks is enough to make the engine run unevenly.
The shaking is transmitted to the body, but the phase disturbance is not enough for the valve plates to collide with the piston bottoms, or the plates fall into the notches on the pistons (present on some engines).
Vibration in diesel engines
The diesel engine is structurally susceptible to vibration at idle and at other speeds. Spread of compression on the cylinders due to uneven wear increases the amplitude of vibration, but as the engine warms up, vibration practically disappears due to thermal expansion of parts.
But if at idle there is a tremor, which is transmitted to the body, it is recommended to check the compression in the cylinders. Note especially applies to engines with a mileage of more than 350-400 thousand kilometers.
A vehicle equipped with a diesel engine shakes when the following faults occur:
- incorrectly set fuel injection advance angle by the mechanical pump;
- faulty injectors (excessive or insufficient fuel supply);
- malfunction of the mechanical high-pressure pump;
- incorrect timing adjustment;
- cylinder or cylinder group malfunction.
Why else can the engine vibrate at idle
Engine vibration at low speeds is transmitted to the body due to:
- A faulty torque converter in the automatic transmission. In the case of improper operation of the clutch, the car does not accelerate well, jerks appear when changing speeds or modes of operation.
- Generator when connecting a powerful load. The problem is characteristic of carburetor engines.
- Injection system automatically increases idle speed when the generator load is increased or the air conditioner compressor is turned on.
- Air deficiency due to dirty filter or connecting hoses, leading to excessive lean mixture. The injector engine controller detects the error and activates the Check Engine warning light in the instrument cluster.
- Damage to the driveshaft, half axles or rubber couplings. Vibration due to run-out is transmitted to the body and is perceived as a shudder when the engine is idling.
The vibration is transmitted to the body in motion when the engine is idling. And at higher speeds, it can be due to wheel imbalance. For example, dirt or ice lodged on the inner surface of the disk causes a strong shaking of body parts and controls, which is intensified in case of defective shock absorbers.
Danger of vibration
Engine vibration is transmitted to the body and adversely affects the life of supports and spars, in some cases stripping threads in welded nuts or causing fatigue cracks. The vibrations are also harmful to the powertrain itself. In addition to destroying hoses or plastic parts, the fan can come in contact with the radiator (on engines with longitudinal mounting and direct impeller drive).
Vibration of the steering wheel at idle (transmitted to the mechanism and column through body parts) creates discomfort for the driver, but does not adversely affect the handling of the car or the resource of the body.
How to reduce engine vibration
A serviceable engine will always shake at idle and increased rpm. Vibrations will be transmitted to the body without causing discomfort to the driver and passengers.
If strong body vibrations are detected, it is necessary to check the engine yourself or in the conditions of the service. The second method is preferable for drivers who are not well versed in the structure of the car.
The correct sequence of actions
To find the source of vibration that is transmitted to the body, which is transmitted to the body when the engine is idling, it is necessary:
- Check the serviceability of the ignition system and inspect the plugs, on which it is not allowed abundant fouling or an increase in the gap between the contacts. On carbureted engines with a trampler is not superfluous to check the ignition distributor and high-voltage wires.
- Check the mounting cushions to the body and subframe, visually determine the serviceability of the support is not always possible. If the rubber insert has tears or traces of fluid leakage, then the cushions should be replaced. But before repair, it is desirable to conduct a diagnosis of the supports in the service.
- Check the fuel supply on the carbureted engine. The presence of debris in the filter indicates contamination of the tank, which leads to vibration at idle. Injector engines are equipped with a fuel rail with a fitting. Connecting a manometer will allow you to determine the pressure of gasoline. It is better to check the work of injectors on the stand in the conditions of the service.
- Check the correct operation of the timing (provided that the vibrations on the body at idle appeared after the replacement of the belt).
- Check the exhaust system. A damaged muffler or torn heat shield on the body may rattle, causing an unpleasant sound to be transmitted to the body. A bent steel plate under the engine crankcase is also a source of vibration and noise.
If after all measures and repairs, the vibration remains and continues to be transmitted to the body, it is recommended to contact the service for a detailed diagnosis of the engine, gearbox and related systems.
But it is important to remember that the intervention of unqualified personnel can lead to permanent damage to the engine or part of its parts.
Regulation of engine operation with a laptop
Computer diagnostics with the help of an adapter connected to the OBD-II connector allows you to read error codes. Further decoding is used to find faulty electronic components.
Do not thoughtlessly reprogram control units in the expectation of disappearance of vibration at idle. Deep diagnostics of the engine can be carried out only in the conditions of the service, equipped with special equipment and having competent personnel.
Replacement of the timing belt
A worn timing belt does not affect the evenness of engine idling. But if the drive was installed with a violation of the phases, the resulting shaking will be transmitted to the car body. In this case, it is necessary to reassemble the parts in accordance with the manufacturer’s requirements.
General sequence of actions when replacing or reinstalling the belt:
- Remove the attachment drives and unscrew the pulley mount.
- Disconnect wiring harnesses, hoses, or other parts that prevent removal of the engine frontal cover.
- Remove the covers and manually turn the crankshaft, checking the alignment of the marks on the gears and engine parts. On a number of engines for alignment of camshafts requires a template, which is installed in the technological holes in the head block.
- Correct the position of the belt and turn the engine several times by hand, checking for correct phasing.
- Install the removed parts and check the engine operation. If vibration at idle is still present and transmitted to the body, continue troubleshooting.
Severe engine vibration at idle, transmitted to the body, most often indicates a faulty transmission. With further operation of the motor, serious breakdowns are possible, timely diagnosis will allow you to detect the defect in time and reduce repair costs.
Have you encountered suspicious engine vibrations, which are transmitted to the body? Have you found the cause of such a phenomenon? Share your experience in the comments with other car owners. Perhaps it will help them to troubleshoot their car.