Difficulty starting the engine can be encountered not only in the cold season. But with a decrease in temperature, long-overdue problems begin to manifest themselves in all their glory. A typical question, which, with the onset of autumn, is increasingly asked on the forums, sounds extremely simple: the car does not start well — what to do? Let’s try to analyze the question in detail.
Globally, only three components are required to ignite the air-fuel mixture:
In the case of the engine, a fourth component is also needed: the fact that this process will order and make it repeat itself stably and regularly.
Based on this simple formula, let’s go through all the components in which there may be a problem. Today we do not consider diesel engines, but we will deal with the most common type of power supply in our country — gasoline.
This is statistically the least likely cause. After all, all interruptions in the flow of air into the engine fit into problems with the throttle valve or idle speed regulator (IAC). But if the damper does not open to the desired angle when the engine is started, then the car will not be able to drive normally either — it will inadequately respond to the gas pedal. We discard this option.
It remains the IAC (also called the idle valve). And here there really may be a deterioration or malfunction of this unit. But we note that in the overwhelming majority of more or less modern cars, the throttle is electronic. This means that the XX regulator is absent there as a class — all engine modes, including starting, are controlled directly by the damper.
By the way, in the case of incorrect operation of the idle valve, interruptions will also occur with, in fact, idling. That is, the malfunction, as in the example with the throttle, will already have complex symptoms.
The second global «whale» of the subject of today’s discussion. There are two diametrically opposite cases: either too little or too much fuel.
On the fly, once the engine has reached operating temperature, the injector efficiency may not be felt at first. And, nevertheless, fuel consumption will gradually increase, and the dynamics will fall. Sooner or later, the owner will still feel that something is wrong with the car, but the first signal to check the injector can be a difficult cold start.
There is also a spring-loaded ball valve in the fuel supply line. It is located in the fitting, which is either connected to the body of the fuel pump, or is itself part of the body. The purpose of this valve is to prevent fuel from draining into the tank after the fuel pump has stopped working. Simply put, if this valve is working properly, then after an hour, two or even ten, the car will start easily and naturally. If the ball is stuck in the open position, then as soon as you turn off the engine, the fuel from the line will immediately merge into the gas tank. And the next time the gas pump is started, it will have to create pressure in the system from scratch — this takes extra seconds, which the starter turns the engine idle.
This is usually due to old and dirty candles. Nevertheless, the honorable second place after candles is occupied by ignition coils. If there is a separate coil for each candle (most often), everything is not so bad. But if there is a common ignition module for all cylinders, its replacement will be expensive, and this device cannot be repaired.
Even 15 years ago, the concept of «checking high-voltage wires» was in constant use among servicemen and just car owners. After all, the wire acted as an intermediary between the ignition coil and the spark plug. This decision went to electronic ignition systems from their «grandfather» — a mechanical distributor («breaker-distributor», if scientifically). But in the end, they refused the intermediate link: the wires often sinned with electrical breakdowns, and in general there was no need for excess resistance. And in the process of «evolution» this rudiment has outlived, giving way to a scheme that we see everywhere now: a separate coil for a candle, or a common ignition module — but also without wires.
In fact, this abstruse phrase hides a simple meaning: the flow of fuel and air, their compression, and then ignition and output from the cylinders are not carried out in a given sequence. The crankshaft position sensor (DPKV) is responsible for ensuring that this procedure is followed. It is he who conducts the orchestra for all four strokes of the engine. Remove the DPKV and the engine will not start.
It so happens that this sensor starts to fail. When the engine is already running, this is not so obvious at first. But getting started can be difficult. Diagnostics is complicated by the fact that with such a «semi-working» crankshaft sensor, it often does not give itself out as an error, even when diagnosed with a scanner.
Of course no. If the reason for the bad engine start fit into this simple algorithm, the services would not be needed. Which, in principle, was quite clearly demonstrated by the practice of our country during the Soviet era. Every happy car owner was not just a driver, but also a mechanic. For many decades, the concept of “fixing up on the service” was inaccessible to our fellow citizens, and sometimes just incomprehensible. We did everything ourselves. But with similar fundamental principles of constructiveness, the complexity of components, assemblies and their interaction on a modern car is incomparable with a car even 30 years ago. Therefore, we will briefly list some more likely causes of unstable engine start.
In fact, everything else that was not included in the basic reasons listed above are sensors. In a modern car, absolutely everything is entangled with them, from the driver’s seat to the wheels. In addition to the classic DPKV, there are also a myriad of auxiliary control and setting sensors.
The stability of the engine start can be directly affected by:
And of course, we cannot but mention the well-known «lambda probe». Its formal name is oxygen sensor. And as you can see, he is in charge of determining the concentration of oxygen in the exhaust gases. Usually, two lambdas are used for each catalyst. The master is located in front of the catalyst, and the control one is located behind it. And contrary to popular belief, even completely faulty oxygen sensors cannot affect the start of a cold engine: until the engine is warmed up, they do not participate in mixture formation. And even if you drowned out, and after an hour in vain turn the starter on a still warm engine, lambda has nothing to do with it. Before it starts working, it must be thoroughly warmed up with hot exhaust gases — this takes at least 10-30 seconds of work. Thus, the lambda probe has no direct effect on the start.
Hopefully today’s article has provided some clarity on why the engine is difficult to start. As always, it does not at all pretend to replace the repair manual, but aims to give a general idea of the processes taking place in an internal combustion engine.