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1. Start the engine and let it idle. Go to the exhaust pipe and listen to the sound of the exhaust. You can put your hand to the end of the exhaust pipe - this way you can feel the interruptions better. The sound should be smooth, "soft", of one tone. Pops from the exhaust pipe at regular intervals indicate that one cylinder is not working due to a faulty spark plug, no spark on it, a failure of the injector, a strong air leak in one cylinder or a significant decrease in compression in it. Pops at irregular intervals occur due to contamination of the injector nozzles, severe wear or contamination of the spark plugs. If pops occur at irregular intervals, you can try to replace the entire set of spark plugs yourself, regardless of mileage and appearance, but it is better to do this after contacting a car service for diagnostics and repair of the engine management system.
2. If the pops are irregular, stop the engine and open the hood. Check the condition of the ignition system wires. The insulation of the high-voltage wires should not be damaged, and their tips should not be oxidized. If there is damage to the wires, replace the faulty wire.
Note. The simplest and most effective way to check high-voltage wires is to check in the dark. Place the car in a dark place, start the engine and open the hood. Inspect the high-voltage wires. If the insulation of the wires is damaged, you will see a characteristic blue-violet spark ("northern lights"). In this case, the high-voltage wires must be replaced.
3. Remove the spark plugs (see "Replacement and maintenance of spark plugs").
Caution! When removing high-voltage wire tips, never pull the wire itself. Grasp the tip directly with your hand and pull it, twisting it from side to side.
4. Carefully inspect the spark plugs and compare their appearance with the photographs provided in the next subsection "Diagnosis of engine condition by the appearance of spark plugs". If the candle is black and wet, it can be thrown away.
5. If all the spark plugs look OK, reinstall them and reconnect the spark plug wires. Cylinder firing order: 1-3-4-2; the cylinder numbering (1, 2, 3, 4) is carried out from the engine crankshaft pulley.
6. Take a spare spark plug. Secure it to the engine in any way.
Connect the high-voltage wire of the 1st cylinder to the spare spark plug. Start the engine. If the misfires do not increase, replace the spark plug in the 1st cylinder with a known good one. Put on the high-voltage wire and start the engine. If the misfires increase, repeat this procedure sequentially with all cylinders to find the faulty spark plug.
Attention! Reliable contact of the spark plug body with the "ground" is mandatory, since if an additional spark gap appears, larger than the gap between the spark plug electrodes, damage to the high-voltage circuit of the ignition coil or the engine control unit is possible.
Attention! Try to carry out the above test in the shortest possible time, since catalytic converters may fail due to overheating if unburned gasoline enters them for a long time, since gasoline will burn in them.
If the engine misfires are not eliminated as a result of the measures taken, check the compression in each cylinder (see "Checking the compression in the cylinders"). Normal compression is more than 1.0 MPa (10 kgf/cm²), a difference of more than 0.1 MPa (1 kgf/cm²) in one cylinder indicates the need for engine repair.
The original article is available on the website fordbook.ru