Why on hot high revs
Content
The idle mode (XX) of an automobile engine with the accelerator released and the transmission in neutral position on all motors, except for the oldest ones, is regulated by separate devices and must be stable. Especially with a fully warmed up engine, when all the conditions for the correct dosing of the fuel mixture are created.
The speed of rotation of the crankshaft at the twentieth is set constructively, the accuracy of its maintenance indicates the serviceability of the material part.
How to determine that the idle speed began to float
Cyclic or chaotic changes in the speed of rotation are clearly visible by the reaction of the tachometer needle or by ear. Any noticeable fluctuations are unacceptable. Old carburetor engines or diesel engines without electronic control may experience speed jumps when changing loads.
Here, the load should be considered not only the engagement of the transmission. The engine has attached units, the energy consumption of which is not constant. It can be:
- an electrician that changes the energy consumption from the generator, thereby loading its belt drive from the crankshaft pulley;
- similar variable load from the power steering pump during its rotation;
- pressing the brake pedal, causing the brake booster to operate;
- turning on the air conditioning compressor of the climate system;
- change in engine temperature.
In modern motors there is feedback through the crankshaft position sensor. The electronic control unit (ECU) notices the difference between the speed set in the program and the actual speed, after which the supply of additional air, fuel, or a change in the ignition timing evens out the situation.
But if there are malfunctions in the system, then the control range is not enough, or the controller does not have time to work out quick changes, the engine changes speed, vibrates and twitches.
What causes high RPMs on a hot engine?
You can generalize the reasons for the increase in speed for all motors. These are changes in the composition of the mixture, problems with the ignition or the mechanical part.
Faults should be specified for each organization of the workflow, a primitive spray of gasoline in a carburetor, a controlled supply in an electronic injection system or diesel engine fuel assemblies.
Carburetor ICE
A distinctive feature of such internal combustion engines is the lack of feedback on speed. The carburetor releases a certain amount of the mixture based on the speed of the flow of air passing through it.
This speed depends on the frequency of rotation, but it is not necessary to wait for an exact reaction to all factors. The motor can lose speed from any load in the form of a malfunction or connection of consumers, and compensation is not provided.
The opposite situation is also possible, when the revolutions are high, but the carburetor idle system can react in the only way - to add more mixture, maintaining these increased revolutions. Therefore, almost everything affects the speed of rotation.
Most often, the operation of the autonomous XX system is disrupted due to blockages in the carburetor. Attempts to adjust lead to unstable operation and a sharp increase in the content of harmful substances in the exhaust, and on the go the engine may stall at the most inopportune moment. Fortunately, carbureted engines are almost gone.
Injector
Noticing an increase in speed, the ECM will give a command to reduce them. The air channel will be covered by a regular regulator, but its capabilities are limited.
A typical situation is the flow of excess air bypassing the control channel. The system will add the appropriate amount of gasoline, the speed will increase. It is impossible to correct the error, channel XX is already completely closed.
An error signal will appear, the controller will go into an emergency mode of maintaining increased speed, since it is not safe to stop the engine.
Diesel engine
Diesels are also different, from the simplest fuel systems with mechanical pumps, to modern ones, electronically controlled by the signals of numerous sensors, but the basis of everything is the air flow measured by the ECU.
A common cause of violations is the recirculation valve, designed to supply part of the exhaust back to the intake. The conditions in which it operates contribute to pollution and failure.
Other culprits are also possible, high pressure pump, sensors, regulators, intake manifold, injectors. A complex diagnosis is needed.
Ways to solve the problem
It is usually not difficult to eliminate the violation, more time is spent on its search due to the variety of reasons.
Mass air flow sensor
The DMRV can give distorted readings, introducing an error into the computer's calculations. The latter is able to easily fend off deception, but usually within small limits.
Then he will simply turn off the obviously faulty sensor, start regulation according to the readings of all the others, increase the speed of the XX and set the error code.
A faulty DMRV is checked according to the scanner data in different modes, its signal must correspond to a typical set. The same can be done with a multimeter, but not in all motors. The sensor needs to be replaced. Sometimes it is possible to wash it and restore it, but you should not always hope for it.
РХХ sensor
In fact, this is not a sensor, but an actuator. It consists of an air valve controlled by a stepper motor.
Problems occur due to contamination of the actuator, the throttle assembly where the regulator is installed in the bypass channel, as well as mechanical wear. The IAC is changed to a new one, and the throttle assembly must be removed and completely flushed.
DPDZ
The throttle position sensor can have a design in the form of a simple potentiometer with a coal road and a slider. This mechanism wears out over time and begins to give out breaks and errors.
It is inexpensive, easily diagnosed by a scanner and quickly replaced. Sometimes it is possible to restore operation by adjusting the position so that the closed damper gives a clear zero to the computer.
Throttle valve
The air supply channel with the throttle is often dirty, after which the damper does not close completely. This is equivalent to lightly pressing the gas pedal, which leads to an increase in speed.
Moreover, no error is generated, since the TPS also signals a small opening. The solution is to wash the throttle pipe with cleaners. Sometimes the same thing happens due to wear and tear. Then the assembly is replaced.
Engine temperature sensor
The composition of the mixture depends on the temperature of the motor. When the corresponding sensor works with a large error, the ECU fixes this as insufficient warming up, adding idle speed.
By comparing the actual temperature with the readings of the scanner, it is possible to identify and reject diesel fuel, after which everything is decided by an inexpensive replacement.
Intake manifold
The entire intake tract must be sealed, since there is a vacuum in it when the throttle is closed. Any leaks in the gaskets or the material of the parts lead to the suction of unaccounted for air, interruptions and an increase in speed.
Diagnostics is necessary using a smoke generator or a carbon test, that is, by spilling suspicious places with combustible sprays.
ECU
Rarely, but ECU errors occur, from old age or water ingress into its sealed structure. The unit can be restored by soldering at a specialist, cleaning the contacts and replacing the elements.
But often it is simply replaced with a new one or a known good one from a car disassembly. In reality, ECU failures lead to more serious manifestations than an increase in speed.
It is undesirable to drive at high speeds. This is an emergency mode, which can lead to new engine breakdowns. But getting to the place of repair is quite allowed on your own.
