A situation where a car refuses to start, and a persistent smell of fuel is heard from the exhaust pipe or engine compartment, is a classic sign. re-enrichment of the fuel-air mixture. An internal combustion engine operates on a strict balance: if too much gasoline is supplied and not enough air, the spark cannot ignite the mixture, and the engine stalls or does not start at all. This phenomenon is often referred to as "plug flooding" and requires immediate attention, as constant cranking of the starter only aggravates the problem, discharging the battery and washing the oil film from the cylinder walls.
There can be many reasons for this behavior: from a simple failure in the electronics to a mechanical failure of the fuel pressure regulator. For owners of injection cars VAZ, Ford or Toyota you have to deal with this regularly, especially in the cold season. It is important not to panic and not to continue to endlessly turn the starter, trying to “blow out” the cylinders, as this can lead to failure of expensive components of the ignition system and catalyst.
In this article we will analyze in detail the algorithm of actions that will help start the engine and identify the malfunction. You will learn how to properly diagnose fuel rail, check the condition of the spark plugs and understand when the problem can be solved on your own, and when the intervention of car service specialists is required. The correct sequence of actions will save you time and money.
Why the engine overflows: the main reasons
The fundamental reason for failure to start with the simultaneous smell of gasoline lies in the violation of the mixture proportions. Ideally, there should be about 14.7 parts of air per part of fuel. If this proportion is violated towards the fuel, the mixture becomes “heavy” and does not ignite from a spark. Most often the culprit is engine management system (ECU), which mistakenly commands the injector opening pulse to be too long.
One of the common causes is faulty sensors that transmit incorrect data to the control unit. For example, if Throttle Position Sensor (TPS) or Mass air flow sensor (MAF) transmits a signal that the engine is running under load or idling with the throttle closed, the ECU can artificially enrich the mixture. Also, overflow is often caused by injectors jamming in the open position, when fuel drips into the manifold even when the engine is turned off.
Another critical symptom is a drop in compression or problems with the ignition system that masquerade as fuel problems. If the spark is weak or supplied at the wrong moment, unburned gasoline flies into the exhaust system, creating a characteristic odor. However, the primary cause is most often the excess amount of fuel in the combustion chamber.
⚠️ Attention: If, after several attempts to start, you feel that the smell of gasoline has become unbearable and black smoke is coming out of the exhaust pipe, stop trying immediately. Prolonged cranking of the starter with filled spark plugs can lead to water hammer if liquid gasoline fills the cylinder completely, which can lead to serious mechanical damage to the piston group.
Understanding the physics of the process helps to localize the problem faster. Gasoline must be in a vapor state to ignite. If there is too much of it, it settles on the cylinder walls and electrodes of the spark plugs, creating a conductive layer that “shorts out” the spark. That is why, when you try to start, the starter spins briskly, you hear “grabbing”, but the engine does not start.
Diagnostics of the ignition system and spark plugs
The first step in troubleshooting should be a visual and technical check of the ignition elements. Spark plugs are an indicator of engine health, and their condition will tell you more about what is happening in the cylinders than any diagnostic tool. To check, you need to unscrew the spark plugs and carefully inspect them.
If you find that the electrodes and threads of the spark plugs are wet, smell of gasoline and have black soot, the diagnosis of “flooded spark plugs” is confirmed. In this state, the spark either does not jump at all, or goes to ground through the fuel layer. Heat number and the spark plug gap also play a role: spark plugs that are too cold may not self-clean, and an increased gap will make it more difficult for a spark to break through in a rich mixture.
Checking high-voltage wires and coils is also required. In wet weather or if there are microcracks in the insulation of the wires, a spark may “break through” to the motor housing, especially if there are traces of oil or moisture on the surface. This phenomenon is often accompanied by a characteristic crackling noise under the hood at night.
To qualitatively analyze the condition of the ignition system, pay attention to the following signs:
- 🔥 Electrode color: black velvety soot indicates a rich mixture, white indicates a poor mixture or overheating.
- 💧 Presence of liquid: if the spark plug is wet and smells of fuel, the cylinder is full of gasoline.
- ⚡ Spark strength: when checking for ground, the spark should be bright blue and break through the gap with a loud click.
- 🔌 Insulation integrity: wires should not have cracks, and coils should not have any traces of breakdown or contact corrosion.
How to properly dry flooded candles?-->
spoiler: There are two main methods: “blowing” the cylinder (full throttle when cranking with the starter without a spark) and calcination. It is necessary to ignite candles with an open fire (gas burner) with extreme caution so as not to damage the ceramic insulator. It is best to gently wipe them with a rag, dry them with a hairdryer and bake them on a safe heat source, controlling the temperature so as not to melt the O-ring.
After checking and, if necessary, replacing or cleaning the spark plugs, it is important to ensure that the gap is correct. A gap that is too small will produce a weak spark that will not be able to ignite a rich mixture, and a gap that is too large will require more voltage, which the coil may not produce. Optimal values are usually in the range 0.7–1.0 mm, but it is better to check the exact data with the manual for your model car.
Checking the fuel system and injectors
If the ignition system is working properly, attention switches to the fuel line. The main suspect here is fuel pressure regulator. Its design includes a membrane that separates fuel and vacuum. When this membrane ruptures, gasoline directly enters the intake manifold through the vacuum hose, causing constant overflow and difficult starting.
Checking the injectors requires a more in-depth diagnosis. A faulty nozzle may “pour” a stream instead of spraying mist, or may not close hermetically after turning off the power supply. This often happens due to dirt, rust from the tank or low-quality fuel. As a result, even when the engine is not running, gasoline continues to drip into the cylinders.
To assess the condition of the fuel system, it is recommended to perform the following steps:
- 🛢️ Check the pressure in the fuel rail using a pressure gauge (the norm is usually 3.0–3.5 bar for injectors).
- 👂 Listen to the operation of the fuel pump: it should turn on when you turn the key and create a characteristic hum.
- 🔍 Inspect the pressure regulator: remove the vacuum hose and check if gasoline is leaking from there.
- 🧹 Rinse the nozzles: use a special cleaning composition or an ultrasonic bath to remove deposits.
Use fuel system cleaner added to the tank as a preventive measure only. If the injectors are already leaking, chemicals may not help, but may only worsen the situation by softening deposits, which will then clog the filters.
It is also important to check the integrity of the fuel hoses and their connections. Microcracks or loose clamps can leak, creating a fire hazard and the smell of gasoline in the engine compartment. This is especially true for cars with high mileage, where rubber elements lose their elasticity.
The role of sensors and ECUs in mixture formation
A modern injection engine is completely dependent on sensor readings. If Coolant temperature sensor (DTOZH) The ECU shows that the engine is cold (for example, -40°C), the control unit goes into warm-up mode and greatly enriches the mixture. If the sensor is faulty and lying, the mixture will be over-rich even on a warm engine, which will lead to overflow.
A similar situation occurs with Mass air flow sensor (Mass air flow sensor). A dirty sensor thread may give underestimated readings about the amount of incoming air. The ECU “thinks” that there is not enough air and pours less fuel, but if the sensor, on the contrary, overestimates the readings or does not work correctly in conjunction with other sensors, the balance is upset. Often the problem is solved by cleaning the sensor with a special spray.
Malfunctions in the operation of the ECU itself or its software are also possible. Electronics glitches, oxidation of contacts in connectors (“chips”), or ground problems can lead to chaotic behavior of the control system. In such cases, computer diagnostics with a scanner will show errors that will help narrow the search.
| Sensor/Node | Problem Symptom | Impact on launch | Test method |
|---|---|---|---|
| DTOZH (Temperatures) | The engine “thinks” it is cold | Strong overflow, black smoke | Measuring resistance with a multimeter |
| MAF (Air flow) | Incorrect calculation of air mass | Unstable idle, excessive consumption | Disabling the chip, checking the dynamics |
| Pressure regulator | Drop or increase in pressure in the ramp | Difficult start, tripping | Pressure gauge, visual inspection of the hose |
| Injectors | Leaking, poor spray | Overflow into a specific cylinder | Bench testing, balancing |
⚠️ Attention: Be aware of high pressure when working on the fuel system. Before disconnecting any fuel hoses or rails, the system must be depressurized, otherwise a high-pressure stream of gasoline may be released, which is dangerous to the eyes and skin.
Algorithm for starting the engine when overflowing
If you find out that the spark plugs are flooded, but there is no way to replace them right now, you can try starting the engine using the “blow through” method. This method is effective if the overflow is not critical and the battery is charged. The essence of the method is to create conditions under which only air will enter the cylinders.
To implement the “purge mode” on most fuel-injected cars, you need to depress the gas pedal all the way and turn the starter for 10-15 seconds. In this position, the throttle valve is fully open, and the ECU (depending on the firmware) can turn off the fuel supply or significantly reduce it, allowing clean air to be pumped through the cylinders and dry the spark plugs.
☑️ Algorithm of actions with flooded candles
If the full throttle method does not help, the spark may be too weak or there is too much gasoline in the cylinders. In this case, it is better to unscrew the spark plugs, wipe them with a rag, dry them and screw them back in. It will take more time, but will give a 99% guarantee of success.
Key point: If, after drying the spark plugs and checking the spark, the engine still does not start and smells of gasoline, the problem lies deeper - probably in the mechanical part (compression) or in the timing (belt/chain has jumped).
After successful starting, do not turn off the engine immediately. Let it idle to burn out any remaining fuel in the catalyst and exhaust system. A strong smell from the exhaust in the first minutes is normal, but it should disappear quickly.
Prevention and seasonal features of operation
The problem “won’t start and smells of gasoline” most often occurs to drivers in the winter. Low temperatures thicken the oil, reduce battery performance and impair fuel volatility. Under such conditions, the requirements for the quality of the mixture and the condition of the ignition system increase many times over.
To minimize risks in the cold season, it is recommended to use winter grades of fuel, monitor the condition of the battery and, if necessary, install pre-heaters. It is also important to use high-quality motor oils with suitable viscosity to facilitate cranking with the starter.
Basic preventive measures include:
- ❄️ Timely replacement of spark plugs: before winter it is better to install a new set, even if the old ones look working.
- ⛽ High-quality fuel: refuel only at proven gas stations to avoid water and impurities getting into the tank.
- 🔋 Battery charge control: a weak battery will not be able to crank the engine at the required speed for high-quality spark formation.
- 🧹 Cleaning the throttle body: removing carbon deposits will ensure the correct position of the throttle body and stable idle speed.
Is it possible to add ether for launch?-->
spoiler: The use of “Quick Start” (ether) is permissible only in extreme cases and in small doses. Excessive amounts of ether can cause detonation, which can destroy the pistons. In addition, ether washes oil from the cylinder walls, which increases wear during cold starts.
Regular maintenance is the key to avoiding such problems. Scheduled replacement of filters (air, fuel), checking the pressure in the fuel rail and diagnosing errors via the OBD-II connector will help identify deviations in engine operation long before it refuses to start.
Why does it smell like gasoline when the car won't start?
The smell occurs due to the fact that unburned fuel is released into the exhaust manifold and exhaust pipe when the starter is cranked. Because the mixture is too rich to ignite, gasoline escapes as vapor or droplets.
Is it possible to drive if the engine is running rough and smells of gasoline?
Highly not recommended. Unburned gasoline burns out in the catalyst, causing it to overheat and melt. In addition, gasoline flows into the crankcase and mixes with oil, which leads to a decrease in lubricating properties and accelerated engine wear.
How often should you change spark plugs?
The service life of spark plugs depends on their type and operating conditions. Conventional nickel spark plugs last 20-30 thousand km, platinum and iridium spark plugs last up to 60-100 thousand km. However, in practice, especially when using low-quality fuel, it is better to change them more often - every 30-40 thousand km.
What to do if the problem remains after replacing the spark plugs?
If new spark plugs are flooded again after a short time, then the reason is not in them. It is necessary to look for a fault in the control system (sensors, computer), check the compression in the cylinders or diagnose the tightness of the injectors.