The situation when a car starts cheerfully on a cold, but sluggishly accelerates after warming up, is familiar to many owners of old and new cars. It is not just an annoying defect, but a signal that the engine control system is not a problem. EBOU The fuel mixture has gone into emergency mode or the physical properties of the fuel-air mixture have changed critically.
The thermal mode of the power unit directly affects air density, oil viscosity and fuel combustion efficiency. When the temperature goes beyond the calculated window, electronics have to sacrifice dynamics to preserve the integrity of the nodes. Understanding the physics of the process will help to quickly find the fault.
In this article, we will discuss in detail the mechanical and electronic causes of thrust loss, explain the role of each sensor and tell you how to distinguish the normal operation of the system from the harbinger of major repairs.
Electronic adjustment and ECU operation
The modern engine is a complex computer that controls every stroke of work. EBOU It's an enriched warm-up program, ignoring some of the sensor readings to get into the mode quickly, but when you reach the operating temperature, the basic algorithm, which is tied to the lambda probes and the knock sensor, comes into effect.
If the system detects overheating or anomalies in combustion, it forcefully impoverishes the mixture or reduces the angle of ignition advance, which instantly strangles the motor, making the response to the gas pedal sluggish. The critical threshold for power discharge is a temperature above 105-110 ° C.After which the protection regime is activated.
Particular attention should be paid to the sensor position of the throttle and MAP sensorWhen they're heated, their contacts can oxidize, causing resistance surges, and electronics perceive this as a mistake and limit torque.
Often drivers forget that even a small fault in the wiring can manifest itself only when the heat expands parts, cold contact can ring normally, and heated - lose signal.
- 🔥 The knock sensor prematurely registers knocks and resets the ignition angle.
- 🔥 The lambda probe gives a false signal about the poor mixture, causing over-enrichment.
- 🔥 ECU goes into the Limp Home mode (emergency course) when the catalyst overheats.
What is the ignition angle?
This is the moment the mixture ignites before the piston reaches the upper dead point, and if the ECU sees the detonation, it makes an angle later, the mixture burns out when the exhaust valve is open, the energy of the explosion is lost, and the exhaust temperature rises.
Problems with the fuel system and nozzles
The fuel system is extremely sensitive to temperature changes, and the main problem that injection car owners face is that they're not the only ones who have a problem with it. steam-coop The petrol in the tank can be cold, but under the hood, where the temperature is high, it boils in the highways.
Fuel vapors are less dense than liquid. When a gaseous mixture enters the injectors, the effective area of the passageway falls, and the cylinder loses fuel, the engine begins to choke, especially under load.
Also worth considering is the thermal expansion of the metal parts of the nozzles. When heated, the nozzle needle can be jammed or, conversely, not keep tight, causing overflow. Fuel pressure regulatorThe diaphragm located on the ramp can also lose the elasticity of the membrane at high temperatures.
In diesel systems, the problem can be fuel heating. If the TNVD overheats from a hot back drain, the viscosity of the diesel fuel drops, the lubrication capacity decreases, and the plunger steam works with gaps without developing the necessary pressure.
⚠️ Note: If after stopping the hot engine the car does not start well ("hot restart problem"), most likely, the problem is in the steam stopper or pressure leakage in the ramp.
☑️ Diagnostics of fuel
Effect of the catalyst state on thrust
The catalytic converter is a filter that burns out harmful substances, and it needs a high temperature to work effectively, but if it's clogged with decay products or melted, it turns into a muffler. The exhaust gases have nowhere to go.
The back pressure in the exhaust system grows exponentially. The engine spends a huge part of its power just to blow the exhaust through the clogged honeycombs. On cold, when the metal is narrowed, the permeability can be slightly better, but when heated, the ceramics expands and completely blocks the flow.
The symptoms of a clogged catalyst are often confused with ignition problems, and the car accelerates to 3000-4000 rpm, and then it hits a wall. Turbocharged engines suffer from this in the first place, as the turbine can not spin due to the resistance in the exhaust.
You can diagnose the problem by temporarily twisting the top oxygen sensor or disconnecting the receiving pipe, and if the dynamics improves dramatically, the path to the gases is closed.
| Status of the catalyst | Impact on power | Body temperature | The sound of exhaust |
|---|---|---|---|
| Norma. | No influence. | 300-500°C | Smooth hum |
| Scored by 50% | Loss of 10-15% traction | 600-700°C | Whistling during acceleration |
| Critical blockage | Loss of >40% of power | Over 800°C (blushing) | Hissing, humming |
| Destroyed. | Risk of Crumbs getting into cylinders | Uneven heating | Roaring, rattling |
Thermostat and cooling system
Thermostat malfunctions are a classic cause of power loss: If the valve is stuck in the closed position, the antifreeze circulates only in a small circle, the engine locally overheats, although the arrow on the dashboard may behave calmly due to the inertia of the sensor.
Overheating of the cylinder head reduces the detonation resistance of the fuel, the ECU has to aggressively shift the ignition, which kills the dynamics, and the hot cylinder walls cause the fuel to detonate. ignitionWhen the mixture is ignited not from a spark, but from contact with a hot metal.
If the thermostat is open, the engine goes to operating temperature for a long time and operates inefficiently in cold weather, but more often the loss of power is due to local boiling of antifreeze and the formation of steam stoppers in the cooling shirt.
It is important to monitor the pump. If the impeller is worn or slips, the circulation of the liquid at high revs is disturbed, and the heat is not removed from the combustion chamber.
Use an infrared pyrometer to check the temperature of the pipes before and after the thermostat, the difference should be minimal after warming up if the thermostat is open.
Mass air flow sensor (MADR)
The mass air flow sensor is the nose of the engine, which determines how much oxygen enters the cylinders, and it works by heating the filament, and when the sensor body is heated or the filament is changed, the readings can float.
If the hot engine is lower in density, if the DMRV is not properly taking into account the temperature of the incoming flow (often due to a malfunction of the built-in air temperature sensor), it will transmit the wrong data on the air mass to the ECU, and the mixture will form the wrong one: either too rich, causing carbon dioxide, or too poor, leading to thrust failures.
Often the problem lies not in the sensor itself, but in the sucking of unaccounted air through the cracked pipe after the DMRV. The hot rubber of the pipes becomes softer, and air begins to be sucked through the microcracks, impoverishing the mixture.
You can diagnose the pump by spraying the carburettor cleaner on the engine, and if the speed changes, the leakage is broken.
- 🌡️ The air temperature sensor (TTP) gives false readings about low temperature.
- 🌡️ The coar on the sensitive element of DMRV distorts the heat transfer.
- 🌡️ Cracks in the intake manifold expand when heated, increasing the sucker.
A faulty DMRV or air suction creates a “poor” mixture, which causes detonation and forced reduction of the ECU power to protect the motor.
Mechanical problems: compression and oil
When the engine heats up, all the metal parts expand. If the engine is worn out, the heat gaps may disappear or become critical. The pistons may bite in the cylinders, and the rings may lose mobility due to coking.
Oil is the main enemy or friend in this process. When you heat it, the viscosity of the oil drops. If the oil pump is worn out, the pressure in the system can drop below the permissible minimum. VVT-i Or the phasers stop working properly because they don't have enough pressure to turn the shafts, and the timing phases get lost, and the power drops.
Also worth mentioning are hydraulic compensators: hot ones, if the oil becomes too liquid or polluted, they can not keep the pressure, causing the valves to knock and the combustion chamber to leak, compression drops, and the engine "does not pull."
In severe cases, piston rings are found to overlap the gaps in the cold, and in the hot one, when the metal has expanded, the gases break through the crankcase, reducing the pressure in the cylinder.
⚠️ Warning: If the loss of power is accompanied by the appearance of blue smoke from the exhaust pipe to the hot one, this is a sign of wear of oil caps or rings - the oil burns, reducing the octane number of the mixture.
Questions and answers
Why does the car lose power only in the heat?
In hot weather, the air density decreases. The engine gets less oxygen for the same cylinder volume. The ECU tries to compensate for this, but the physical limit of occupancy is reached. In addition, in heat, the intercooler works worse, increasing the boost temperature and the risk of detonation.
Can bad gasoline cause a loss of hot cravings?
Yes, low-octane gasoline or impurity fuels have less resistance to detonation. On a warm engine, when the temperature in the cylinders is high, the risk of self-ignition increases, the ECU detects detonation and aggressively strangles the engine, releasing power.
How does a clogged air filter affect?
A clogged filter creates resistance to airflow, and on a cold engine it can compensate for this by revving, but on a hot engine, when the air demand is maximum, there is a "choking effect": the mixture is overenriched, the combustion deteriorates, the power drops.
Do I need to wash the nozzles when losing power?
If the problem is caused by heat and is accompanied by uneven operation, flushing can help, but first check the pressure in the fuel ramp and the condition of the filter fine cleaning, as they affect the fuel supply more than the shape of the spray torch.