When the engine of petrol engines has a jerk function, the cause may be due to the ignition system or to the electronic management system or to a failure of some sensor (such as, for example, the engine rpm) or, finally, to the stage. Generally, these anomalies are also signalled by the engine failure warning present in the instrumentation. If the car is powered by diesel fuel, the problem can also be caused by problems with the injectors, the clogged diesel filter or, again, the fuel altered by sludge or by the presence of water. The resolution of all these problems requires professional intervention.



If you notice a drop in engine power, the problems may be due to the clogged fuel filter or the particulate filter (Fap), to a failure of the electronic management unit, to the airflow sensor faulty, to the breakdown of the Egr valve (recirculation of drain) or the fuel pump that is not working. To solve these problems, however, you need to go to a workshop. The same choice, inevitably, must be made if the problem derives from the leakage into the oil cylinders, which dirty the spark plugs and injectors, or from the poor tension of the timing belt (or chain) which, therefore, transmits the motion from the crankshaft to the camshafts in order to modify the tuning of the intake/compression and burst/exhaust phases, affecting the regularity of engine operation. Power drops and engine operating irregularities can also be caused by the incorrectly adjusted clutch that is about to give up, a problem usually anticipated by its slipping: when the accelerator sinks, the engine revs up but the machine moves delayed (and very slowly compared to expectations) or does not move completely. Again, professional intervention is required.



The car that suddenly switches off while driving is a serious inconvenience.It may be due to the electrical system, the ignition system or the failed fuel system or even altered petrol or diesel. Consequently, to identify which of these problems leads to the engine stopping and then to solve it, it is advisable to contact a professional.



The machine is flooded when the petrol engine does not start due to an accumulation of mixture in the cylinder that has wetted the spark plugs. This is hardly the case with modern injection cars, while it is quite common on older carburettor models. Understanding that the cause of the ignition failure is due to this inconvenience is simple since the starting attempts – which, in reality, can also trigger an ignition principle – are accompanied by a strong smell of petrol and followed by a “puff ” the final. At this point, it is useless to insist, better to wait a few minutes if you are not able to disassemble the candles to dry them. Then, to turn it on, sink the accelerator and simultaneously start the start. 


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The automatic increase in the number of revolutions of the car when stationary can be caused by various problems. The only one that can be considered normal is due to the fact that the engine has not yet reached the optimum operating temperature after a long stop, especially in the cold season.

If the symptom occurs even when hot and in other situations, you must rely on a professional because in a petrol engine the causes of this defect can be attributable to elements of the fuel system that are out of phase, to the intake of air from the gasket of the manifold, to a problem with the valves or to the distribution assembly, to the advance of the ignition out of place and, finally, also to the fuel dirty or containing water.

The use of a mechanic is also advisable if you are dealing with a diesel engine.



The belt broke is a definition that should be replaced with: one of the belts in the engine has broken. The belts are moved by a pulley at the end of the crankshaft and transmit the movement to various mechanical parts. The breakdown of the distribution one – which usually the houses recommend replacing around 100 thousand kilometres, but which can break even earlier due to mechanical anomalies such as wear of the guide bearings or an unexpected misalignment – can cause serious damage such as failure of the crankshaft, pistons and valves. However, noticing that the timing belt is about to break is not easy, since in almost all engines it is protected by a crankcase.

Instead, the so-called auxiliary or service belt – drives the water pump, the air conditioner compressor, the alternator and on the older cars also the fan – makes a visible path, so you can guess if it is deteriorating simply by opening the bonnet. For their replacement, it is necessary to rely on a mechanic.



When the machine disperses smoke, the causes are overheating of the engine or a start of fire which, for its part, also generates an acrid burning smell.

Overheating, normally anticipated by the lighting of the cooling circuit light and by the hand of the relative thermometer which moves towards the higher degrees, is due to a malfunction of the circuit and is always accompanied by dispersion of smoke from the engine compartment. When you come across this situation, you must stop as soon as possible and turn off the engine to avoid damaging the cylinder head gasket. Then, by inserting the ignition contact but without starting the engine, it is necessary to turn off the air conditioner and turn on the heating to the maximum, so that its circuit removes heat from the engine.

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To obtain the same result, also open the hood of the engine compartment, wait for some time without touching anything to avoid getting burned and, then, check whether in the expansion tank of the cooling circuit – normally transparent and placed on one side of the compartment – the level is below the notch which indicates the minimum. In this case, but only after waiting for the engine to cool down completely, you can carefully open the tank cap and top up.



It is unorthodox but in case of an emergency – that is, if you are not travelling with coolant in tow, as is normal at the bottom – you can also top up with normal water. Once the level is restored, you can restart the engine and see if everything has returned to normal and the problem only surfaced because the level of the coolant had not been checked for some time. If, on the other hand, the temperature rises immediately, the engine must be turned off to reach a workshop, because the problem is serious: broken water pump, burnt head gasket, radiator fan faulty, sleeves or radiator damaged even if in the latter cases the inconvenience produces clearly visible leaks on the road surface.

If you are sure that the workshop is not far away, you can take short stretches of road and stop as soon as the situation returns to critical, wait for the temperature to drop and then repeat the whole process described until you arrive at your destination. Otherwise, you need to call a tow truck.


In case of fire

A fire principle affecting the engine compartment – it can be triggered by a short circuit or by gasoline leaks – must instead be tackled by stopping immediately, leaving the car and calling for help. Under no circumstances should the bonnet be opened to avoid fueling the flames. If, on the other hand, the event occurred while it was already open, it is good to move away, going upwind of the car (i.e. on the opposite side from the direction to which the smoke spreads) and wait for help.

If you have an on-board fire extinguisher, evaluating the risks for your safety well, you can direct the extinguisher, with quick and intermittent launches, towards the engine compartment.

The same can be done if the smoke dispersion occurs in the passenger compartment, once the area from which the smoke comes has been identified.



When the exhaust of the machine disperses smoke, it is possible to understand if the engine is affected by some inconvenience. After a stop in the cold season, thick white smoke may escape from the exhaust. In this case, it is condensation, which disappears when the engine reaches the optimum operating temperature.

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However, if the phenomenon also emerges with the engine warm, the problem is due to infiltration of coolant into the combustion chamber, which may be due to the damaged cylinder head gasket or (and are much more serious cases) to the cracking of the monobloc or cylinder head. The resolution of these problems requires the use of a mechanic.

The intervention of a specialist is indispensable even when the exhaust disperses blue/blue or black fumes.

The blue smoke, which almost always appears accompanied by the typical smell of burnt oil, indicates that an excess of lubricant arrives in the combustion chamber. The phenomenon, which obviously also implies an increase in oil consumption, maybe due to inadequate conditions of piston rings, cylinder liners and pistons if it occurs in acceleration, while if it appears in deceleration it indicates that the excess of lubricant is due to the excessive play between the stems and the valve guides.

Black smoke indicates a less serious problem but must be solved by an expert who must intervene on the carburation too rich to regulate it adequately. The anomaly may be due, however, also to the occluded air filter, therefore a preventive verification of this component can avoid resorting to an intervention in the workshop.

Finally, in diesel engines the smoke – dark in colour – can be due to the irregular combustion, caused by the excessive delivery of diesel fuel by the fuel system.



The problems that a car’s LPG system can cause range from the engine that does not run on petrol or gas to the irregular functioning both at idle and at other engine speeds, up to the fact that LPG is a little weak in acceleration, does not reach maximum power and, finally, consume more than necessary. All these problems, given also the delicacy of a gas system, must be solved by resorting to a professional.

In fact, they are almost always attributable to the components of this fuel system, therefore they can be linked to the pipes or solenoid valves, the reducers or the injection system to be registered, the electrical system to the tank.

In addition, some cars may also complain of operating irregularities due to the timing of the distribution and the valve seats, but the continuous evolution of petrol engines is decreasing the size of this case. In essence, these drawbacks may concern some not very recent design models.



The increase in temperature indicated by the onboard thermometer suggests stopping and opening the engine hood to find any leaks from the cooling system. If you notice liquid coming out of the radiator, you should immediately go to the nearest workshop or, better still, call a tow truck. In an emergency, try adding water to the pan, allowing the engine to cool well. In the event of a “chronic” rise in temperature, the cylinder head gasket is likely to be replaced, and is the most demanding case in economic terms; other causes may be the breakage of the radiator thermostat, a clogging of the radiator itself or a malfunction of the water pump due to the impeller.

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