The situation when the car cheerfully starts "cold", but after reaching the working temperature thrust This behavior of the powertrain indicates that the control systems are not working properly or that mechanical malfunctions occur when parts are thermally expanded or when the ECU is changing.
Primary diagnosis is often complicated by the fact that on a cold engine all parameters can be within the normal range, and errors in the memory of the onboard computer are not recorded. The driver feels only loss of power, failures when pressing the accelerator pedal and the inability to gain familiar speed, which makes the operation of the vehicle dangerous, especially when overtaking.
In this article, we will look at the root causes of power loss, analyze the effect of temperature on sensors and fuel equipment, and suggest an algorithm for finding a fault. Understanding the physics of the processes will help you to quickly localize the problem and avoid costly repairs in the service.
The influence of temperature regime on the work of ECUs and sensors
The modern internal combustion engine is controlled by an electronic unit that builds a fuel-air mixture based on the readings of many sensors. coolant temperature sensor (TTP)If this sensor transmits incorrect data that the engine is still cold, the ECU continues to hold the enriched mixture, which leads to fuel overrun and loss of dynamics after real warming up.
The blockage of traction can be caused by protective algorithms, where when the system detects the risk of overheating or detonation, it forcibly impoverishes the mixture or limits the angle of ignition advance, resulting in the driver's effect of "suffocating" the engine, which does not want to spin above 3000-4000 rpm.
⚠️ Attention: Ignoring the symptoms of loss of traction can lead to critical overheating of the catalyst or burnout of the valves due to violation of thermal gaps.
Also worth considering is the operation of the EGR system: On a cold engine, the EGR valve is closed, but when warmed up, it starts to open to reduce exhaust toxicity. If the valve is jammed open or leaky, too many exhaust gases enter the cylinders, displacing fresh air, which directly affects the power.
Problems with the fuel system during heating
One of the most common reasons why thrust When the operating temperature is reached, there is a steam stopper in the fuel line or a malfunction of the gas pump. When the fuel in the tank and ramp is heated, the fuel expands, and if the ventilation system of the tank is clogged or the pump overheats, the gasoline supply becomes unstable.
The clogged fuel filter also manifests itself under load and when heated. Cold fuel has a different viscosity, and the heated one passes through small holes more easily, however, if the filter is critically clogged, the throughput drops, and the engine begins to starve at the moments of a sharp opening of the throttle.
The nozzles can lose their performance or, conversely, "pour" fuel when the temperature specifications of the electromagnetic valve change, which upsets the balance of the mixture, making it either too poor (failures, jerks) or too rich (black smoke, the smell of gasoline).
☑️ Diagnostics of the fuel system
A pressure gauge must be used to diagnose accurately, the pressure in the fuel ramp must remain stable both at idle speed and under load, and a sharp jump or a smooth drop in pressure will indicate the need to replace the pressure regulator or the pump itself.
Failures in the ignition system and coils
The thermal breakdown of the insulation of high-voltage wires or ignition coils is a classic cause of power loss. Cold microcracks in the insulation can be compressed, and the spark slips through correctly. However, as materials expand from heating, the breakdown resistance drops, and the spark begins to "go to the mass" without ignitioning the mixture in the cylinder.
Ignition plugs are also critical: an incorrectly selected potassium number can lead to kalyl ignition or, conversely, to fouling with soda at certain temperature regimes. If the gap between the electrodes is broken or the electrode is burned out, the quality of the spark will be unsatisfactory precisely when warmed up.
How to check the coil without replacement?
There is a method of visual inspection in the dark: when the engine is running, you can see "dancing" sparks of breakdown on the coil body, and spraying suspicious areas with spray water from the spray gun helps - if the engine starts to triple harder, a break is found.
The ignition module (switch) on some older models of cars tends to shut down when overheated, which looks like a sudden loss of traction that returns after cooling down, in which case the installation of additional cooling or replacing the module with a more modern analogue helps.
Mechanical Causes: Compression and Heat Gaps
Mechanical wear of the engine often manifests itself through a change in compression when heated. When pistons, rings and cylinders are heated, they expand. If the wear is large, the expansion can lead to a decrease in the tightness of the combustion chamber, and the compression drops, which directly reduces the engine power.
Special attention should be paid to thermal gaps of valves. If the gaps are not adjusted (too small), then when the cylinder head is heated, the valve stops closing tightly, which leads to a breakthrough of gases into the exhaust manifold and loss of compression. The engine starts to work unstablely, and the thrust disappears.
| A symptom. | Probable cause | Method of verification |
|---|---|---|
| The engine is going hot. | Coil or candle failure | Turning off the cylinders |
| Falling oil pressure | Wear of liners or pumps | Measured with a pressure gauge on a warmed-up engine |
| Whistling or knocking when heated | Belt tensioner or hydrocompensators | Acoustic diagnosis with a stethoscope |
| Black smoke from the exhaust | Re-enrichment of the mixture | Emission analysis or candle colour |
Hydrocompensators can also cause problems, and when you heat up, the oil liquefies, and if the oil feeds to the compensators are clogged with wear products, they stop making up for the gaps, causing noise and disruption of the gas distribution phases.
Intake system and air suction
Unreported air suction is a frequent culprit for unstable work. When heated, the plastic elements of the intake manifold and rubber pipes expand, which can open microcracks that are invisible to cold. Excess air impoverishes the mixture, and the ECU does not have time to adjust the fuel supply, causing thrust failures.
An idle valve (RX) or a throttle flap contaminated with soot can be wedged at a certain temperature, and it has the ability to expand or change its structure, preventing the mechanism from taking the correct position, which confuses the balancing of speed and thrust.
Use a smoke generator to find the air sucker, and the smoke is great at showing even the smallest leaks in the inlet tract that you can't hear.
The throttle position sensor (TRP) is another candidate for replacement, and its variable resistor wears off over time in commonly used positions, and when heated up, the resistance can float, sending the wrong signal to the ECU to open the valve, which leads to a wrong load calculation.
Diagnostics of exhaust system and catalyst
A clogged catalytic converter creates backpressure in the exhaust system. On a cold engine, the gases are smaller and pass through the cells of the catalyst more easily. As you warm up, the exhaust gas volume increases, and if the passage section is clogged with burnout products or destroyed ceramics, the engine begins to "gap".
You can test this by twisting the lambda probe in front of the catalyst and starting the engine. If the thrust is restored, the problem is guaranteed in the exhaust system. Operating a car with a clogged catalyst is dangerous: pressure can squeeze out the crankshaft boulders or cause valves to burn out.
⚠️ Warning: If a catalyst is suspected of breaking down (ceramic crumb), the engine should not be started, as dust can get into the cylinders through reverse cotton and cause bullies.
It is also worth checking the exhaust system for dents or inflections that may have formed after hitting road bumps, and even a slight tubing can be a critical obstacle to the flow of gases at high revs.
Comprehensive verification and algorithm of actions
To find a problem effectively, you need to be methodical, starting with the least expensive procedures, and the first step should always be computer diagnostics, even if the light bulb is the first step. Check Engine Hidden errors or incorrect readings of sensors (for example, a lambda probe) can only be seen in real-time graphs.
Then you have to check the air filter and the inlet pipes, and often the problem is the commonplace things: the cracked tube after the intercooler or the clogged cabin filter (which affects the operation of some ventilation systems), and then check the fuel pressure and the condition of the spark plugs.
90% of thrust loss after warming up is due to three factors: faulty DMRV/BLD, failure of the ignition coil or clogged fuel filter.
If simple methods don't work, we need to move on to measuring the compression on the hot engine and checking the pressure of the oil, which will give an understanding of the mechanical health of the motor. In complex cases, when the symptoms are floating, an oscilloscope may be needed to analyze the signals of sensors and injectors.
Why does the craving only disappear in the heat?
In hot weather, air density decreases, which in itself reduces engine power, if this is added to overheating of the intake air (due to a faulty intercooler or radiator) or the propensity of the fuel system to vaporize, the loss of traction becomes critical, and in the heat, the cooling system works worse, which can provoke the ECU to go into emergency mode.
Can bad gasoline cause a loss of hot thrust?
Yes, low-octane fuel or impurity gasoline can cause detonation when warmed up, when the compression ratio and temperature in the cylinders increase. ECU, fixing the detonation, will aggressively shift the ignition angle, which will lead to a sharp drop in power and thrust.
How does a faulty lambda probe affect traction?
A faulty lambda probe can send a false signal about a poor mixture, causing the ECU to re-enrich it, and on a hot engine, this leads to black soak on candles, a drop in combustion efficiency and, as a result, loss of traction and increased fuel consumption.