Ignition misfires: signs, causes and repairs

They say that it is useless to reinvent the wheel – everything has already been invented before us. So it is with an internal combustion engine. It is constantly being improved, but the principle of operation has remained the same for many years. And problems too. Powertrain malfunctions affect everyone, and misfires are not the last on a long list of possible troubles.

To understand what misfire is, you need to understand how the cylinders work in the engine. In a nutshell, the energy of the fuel turns into the force of motion in the cylinders. The fuel is ignited there and makes the cylinders go around the cylinder. During a misfire, the fuel / air mixture in one or more cylinders ignites separately from the others or does not ignite at all. Failure of one or several cylinders dramatically reduces engine power, increasing fuel consumption.

Malfunction symptoms

• When a similar problem occurs, the engine with a carburetor often stalls, and a loss of power is also felt. Fuel from the “broken” cylinder enters the exhaust system. The smell of fuel, characteristic pops and gunshots in the muffler indicate a misfire.
• If the engine is injector, the malfunction is easy to notice by similar signs and a tangible shaking of the car. Additionally, the error is stored in the memory of the electronic control unit and displayed as a special check icon on the dashboard. Sometimes the system automatically shuts off the fuel supply to the “conflict” cylinder.

Causes of misfiring

Among the many reasons for the ignition malfunctioning, the main ones are:

1. Failure of elements of the ignition system – armored wire, spark plugs, coil or interrupter-distributor (distributor in carburetor internal combustion engines). In addition, at low temperatures in the candle wells, condensation may form, which can cause “penetration” into the block.
2. Malfunctions in the fuel-air system can be associated with clogged dirt and deposits in the injection nozzles, air and fuel filters. These ailments are manifested in the “triplet” of the engine at idle, which disappears after warming up. An open circuit in a single injector due to unstable power supply can also interfere with fuel delivery.
3. Low compression in all cylinders or its non-uniform distribution indicates wear of the elements of the cylinder-piston group or malfunctions in the operation of the gas distribution mechanism (timing). In this case, the fuel-air mixture is compressed with a lower pressure, which makes it difficult to ignite.
4. Incorrectly adjusted valve clearance can lead to a violation during the compression stroke of the tightness of the entire chamber. The lack of an optimal fit of the valve disc to the seat, as well as burnout of the valve, will become the reasons for misfiring.
5. Poor fuel quality, leaks, or low delivery pressure due to improper operation of the fuel pump can also cause misfire. To identify the problem, it is necessary to check the serviceability of the pressure regulator in the fuel rail. It is equally important to ensure that there is no air leakage or water ingress into the fuel tank.
6. Failure in the operation of the electronic control unit entails the transmission of an incorrect signal from the sensors to turn off the injectors. Therefore, the engine begins to “triple”, there is a misfire. In such cases, it is better to check the ECU firmware and sensors of the electronic engine management system.

Self-diagnosis of engine malfunction

Ignition misfires can occur both against the background of a simple defect in the spark plug, and due to the failure of an entire unit of the power unit. To understand what is happening with the car, it is important to know how to determine the misfire. Depending on the presence of an ECU in the car, diagnostics can be carried out in two ways.

For vehicles with the electronic control unit

It is quite easy to diagnose a malfunction using an ECU. Connect the auto-tester using the OBD connector and find the decoding of the detected errors. Codes P0301, P0302, P0303, P0304 indicate problems in one of the four cylinders, armored wires, candles or gaskets associated with them in accordance with the last digit of the code. If the tester shows error P0300, then you need to check the entire system as a whole, including filters and the composition of the combustible mixture. Codes P0201, P0202, P0203, P0204, etc. indicate malfunctions in the injectors. (according to the number of cylinders in the power unit). Code P0400 describes a problem in the exhaust manifold.

Domestic models are often equipped with old-generation ECUs. It is better to change such a system in authorized service centers for an updated one that is compatible with the electronics of the car as a whole. Modern blocks make it easy to detect misfire in specific cylinders.  

For vehicles without electronic control unit

It is difficult to diagnose misfire in the absence of an ECU. Since a pair of cylinders can fail at once, each of them will have to be checked manually. To inspect the condition of the cylinders and piston rings, it is necessary to dismantle the valve covers. During the examination, it is also important to make sure that the armored wires, candles and electronic parts are working.

Use an ohmmeter to measure electrical resistance in high voltage wires. If the values ​​are not valid, the wires must be replaced. In addition, you should check the condition of the fuel pump and measure the compression indicators in the cylinders. A carburettor-type motor requires special diagnostics directly from the carburettor.

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