Multiple misfires in Priora

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Error code P0300 indicates a violation of the ignition order , which stands for random multiple misfires of the cylinders ; in English, the diagnostic tool displays: “Random cylinder misfire detection system.” If a misfire is detected in a specific cylinder, then the last digit “P030x” will change to 1, 2, 3, 4 and so on up to 6 or even 12, depending on which particular “pot” the misfire is in. So error P0300 is derived from errors such as P0301, P0302, P0303, P0304. Most often they occur due to a lack of spark, a fuel supply failure or problems with the exhaust gases.

Let's look at the list of possible causes of misfires, why error p0301, error p0302, error p0303, error p0304 or others of this kind appears, the consequences and methods of elimination, in more detail.

Symptoms of malfunction

The main driver symptom of a P0300 is the MIL (malfunction indicator light) illumination. It is also called Check engine or simply “check light”.

They can also appear as:

The “Check engine” warning light on the control panel will light up (the code will be stored in the ECM memory as a malfunction).
The engine stalls or has trouble starting.
Floating speed, as well as attempts to stall at idle.
Jerking/misfire at idle or under load.
Poor speed gain.
Increased fuel consumption.
Reduced engine power.
Smell of fuel from the exhaust.

This malfunction is considered serious and must be corrected as soon as possible. Because prolonged driving with a misfire can cause costly damage to the engine and catalytic converters.

A misfire means the fuel is not being processed in the combustion chamber. This can happen for a variety of reasons. To determine the root of the problem, all options must be tested. Starting from the simplest to deeper problems. The search should be done in the following order:

They usually start with the spark plugs. This is the most common cause of cylinder failure. First you need to inspect the candle visually. In working condition, it should be light sand color. If the spark plug is black or gray, you need to clean it. To do this, it is annealed over fire and cleaned with fine sandpaper. Another equally common cause of spark plug failure is a broken gap. It can be both large and small. To eliminate the malfunction, the electrode is pressed out or, on the contrary, pressed, adjusting the gap. After all the steps, you should check the operation of the candle. The spark it creates should be white and blue. This is described in detail in the article “What should be the gap on the spark plugs”;

Faulty injectors. Engine trouble often occurs due to problems with the condition of the injectors. Usually this malfunction is shown by computer diagnostics. The cause is often poor quality fuel. It clogs the injectors and they stop functioning normally. This can be treated by flushing the power system; in extreme cases, you will have to replace the faulty part. This problem can occur on both gasoline and diesel units;
Low compression. This is checked by measuring this indicator. If it is less than 11 points, then measures should be taken to repair the engine;
Incorrect timing adjustment. This usually occurs due to wear of drive parts. Sometimes the reason is a failure in the settings of the hydraulic valve compensators;
Air entering the fuel system. This could be damage to the intake manifold or a change in the condition of the injector rings. Most often, this problem is accompanied by misfires in different cylinders. You should find the cause and remove it.

How to detect a malfunction yourself

We also recommend reading our expert’s article, in which he talks in detail about what a contactless ignition system is.

Be sure to read our specialist’s article, which tells you how to set the ignition correctly.

In cars with ECU

In cars with an ECU, troubleshooting is a fairly easy task. To do this, you need to connect an autotester and find the error code. If among the error codes there is an indication of a specific cylinder, then you should pay special attention to the condition of the element. Perhaps the problem is hidden in the armor wires or spark plugs that go to this cylinder. The gaskets may also need to be replaced. If a complex error (p0300) is issued, then you should pay special attention to the quality of the fuel and the filter.

Even domestic cars now have electronic units installed. If the car initially has an ECU, but its performance leaves much to be desired, then you can replace the part at a certified service station. The new “brains” must be compatible with the previous model. Thanks to the new electronic control units, you can easily find misfires in the 1st and 4th cylinders of the VAZ-2114 or on any old foreign car, as well as diagnose the operation of the 2nd and 3rd cylinders without unnecessary hassle.

Possible solutions

If there are no symptoms, the easiest thing to do is reset the code and see if it comes back.

If there are symptoms such as the engine stumbling or hesitating, check all wiring and connectors leading to the cylinders (such as spark plugs). Depending on how long the ignition system components have been in the vehicle, it may be a good idea to replace them as part of your regular maintenance schedule. I would recommend spark plugs, spark plug wires, distributor cap and rotor (if applicable). If not, check the coils (also known as coil packs). In some cases, the catalytic converter has failed. If you smell rotten eggs in your exhaust, your cat's converter needs to be replaced. I have also heard that in other cases the problem was faulty fuel injectors.