The situation when the starter vigorously rotates the crankshaft, but the engine is silent, is a classic problem for owners of diesel cars, especially in the cold season. Unlike gasoline engines, which require a spark to ignite, diesel fuel ignites from high pressure and compression temperature. If this process is disrupted, the car will remain stationary, despite a working battery and starter.
Drivers often panic, not understanding where the traction has gone and why yesterday the car started at half a turn. However, in most cases the problem lies in one of three systems: fuel, starting system or compression. Understanding the physics of the combustion process will help you quickly localize the fault and avoid unnecessary costs for tow truck services.
In this article we will examine in detail the main reasons why diesel engine refuses to start, and let’s look at the algorithm of actions for self-diagnosis. You'll learn to differentiate the symptoms of glow plug failure from fuel delivery problems, and you'll also learn how to check for air in the system without fancy equipment.
Problems with glow plugs and preheating system
The first thing you should pay attention to during a cold start is the serviceability of the glow plugs. In a diesel engine, the air in the cylinder must be heated to a certain temperature in order for the injected fuel to ignite. If glow plugs are faulty, the temperature in the combustion chamber is insufficient, and ignition does not occur, even if the starter turns perfectly.
Typically, a malfunction is indicated by an indicator on the dashboard in the form of a spiral. If it blinks or does not light up at all, this is a reason to check the circuit. However, even if the light is on, one or more spark plugs may be dead, which is critical for starting in cold weather. On modern engines with Common Rail, the control system can block starting if at least one element malfunctions.
Diagnostics can be carried out with a multimeter by testing each spark plug for resistance. A working part should show low resistance, usually in the range of 0.6 to 2.0 ohms, depending on the model. An infinitely large resistance will indicate a break in the spiral, and such a spark plug will have to be replaced.
- 🔥 The glow plug has burned out and does not heat the combustion chamber.
- ⚡ The spark plug control relay or delay timer is faulty.
- ❄️ The power supply contacts to the candles have oxidized.
- 🔋 A weak battery charge does not allow the candles to heat up to the desired temperature.
⚠️ Attention: Do not try to push start or tow the engine if you suspect a problem with the glow plugs in severe frost. This can lead to irreversible damage to the piston group due to detonation or water hammer (if a lot of fuel gets into the cylinders).
To quickly check the glow plugs without removing them from the engine, you can apply voltage directly from the battery through a thick wire. A working spark plug should begin to glow red hot within 5-10 seconds. Be careful, the wire will get very hot!
Air entering the fuel system
One of the most insidious causes of diesel failure is airing of the fuel line. A diesel engine is extremely sensitive to the tightness of the fuel supply system. If even a small air bubble appears in the line, it breaks the continuous flow of liquid, and fuel stops flowing to the injectors at the required pressure.
Air can enter the system through microcracks in the fuel hoses, a loose fuel filter, or through the booster pump O-rings. This often happens after replacing the filter, if the technician forgot to lubricate the rubber seal with oil or did not tighten the housing properly. The reason may also be that the tank is empty to the bottom, after which the pump begins to circulate air.
To fix the problem, you need to find the leak and remove the air plug. On many cars, a manual bulb pump or a special screw for bleeding air from the filter is provided for this. The process is called “bleeding” and requires patience, as sometimes you have to crank the starter for a long time, taking breaks so as not to burn it.
Algorithm for pumping the system:1. Unscrew the air bleed screw on the fuel filter.
2. Press the manual booster pump (if equipped) several times.
3. Wait until the fuel appears without bubbles.
4. Tighten the screw and try to start the engine.
☑️ Checking the tightness of the fuel
If after a long period of bleeding the engine still does not start, it is possible that air is entering through the fuel intake in the tank or through the high pressure fuel pump (HPF) itself. In such cases, specialized equipment and transparent diagnostic tubes are indispensable.
Malfunctions of the high pressure fuel pump (HPF)
The heart of the diesel fuel system is injection pump. It is this that creates the colossal pressure necessary to atomize fuel in the combustion chamber. If the pump is worn out or its plunger pair is out of order, the pressure in the ramp does not reach the minimum threshold required to open the injectors.
Symptoms of a fuel injection pump malfunction often increase gradually. First, the engine begins to start worse when “hot”, black smoke appears from the exhaust pipe, and thrust drops. At a critical moment, the pump simply stops pumping fuel in the required volume. Another common problem is a jammed pressure regulator or failure of the fuel cut-off solenoid valve.
Diagnosing fuel injection pumps in garage conditions is difficult, since a pressure gauge designed for hundreds and thousands of bar is required. However, an indirect sign may be the absence of a characteristic sound of the pump when the ignition is turned on or its operation is too quiet.
| Symptom | Possible cause in fuel injection pump | Action |
|---|---|---|
| Engine won't start | Solenoid valve faulty | Check for power supply to the valve |
| Difficult starting "hot" | Wear of plunger pair | Measurement of compression and pressure in the ramp |
| Floating speed | Pressure regulator dirty | Flushing or replacing the regulator |
| Knock during operation | Shaft bearing failure | Urgent pump repair |
Injection pump resource
Modern Common Rail pumps are designed for a range of 200-300 thousand kilometers, but are extremely sensitive to the quality of the fuel and the lubricity of the diesel engine. The use of lubricant additives can extend the life of the pump in harsh climates.
Injection pump repair requires high qualifications and cleanliness. If one grain of sand gets inside the pump, it can damage the entire expensive injection system, so opening the unit in the dust of a garage is strictly not recommended.
Clogged injectors and spray problems
Injectors are the final element of the system that supplies fuel to the cylinders. Over time, carbon deposits form on their nozzles and deposits form inside. If the nozzle "pours" instead of creating mist, or if it is completely clogged, ignition will not occur.
In modern systems Common Rail The gaps in the injectors are measured in microns. The use of low-quality fuel or water entering the tank leads to corrosion and rapid failure of these parts. Often, an injector may be mechanically functional, but the electronics do not send an opening signal to it due to a broken wiring or a malfunction of the ECU.
You can check the injectors using the exclusion method, turning off the fuel supply to each of them one by one (on old engines) or reading the injection correction data through a diagnostic scanner. If the correction reaches the maximum values (+/- 2-3 mg/cycle), the injector needs to be replaced or repaired.
- 💧 Water in the fuel caused corrosion of the atomizer.
- 🌫️ Carbon deposits on the nozzle needle disrupted the spray pattern.
- ⚡ Broken winding of the injector solenoid valve.
- 🧱 Mechanical jamming of the needle in the closed position.
⚠️ Attention: When checking injectors using the “disconnect” method with the engine running, be extremely careful. High pressure in the system can pierce the skin, causing severe injury. Never check the tightness of the injectors with your hands!
Replacing a single injector on common rail systems often requires programming new codes (IQ codes) for each cylinder via a diagnostic scanner, otherwise the engine will run rough.
Problems with compression and gas distribution mechanism
If the starter turns vigorously, the spark plugs and fuel are in order, but the engine is silent, you should think about the mechanical part. Diesel fuel requires high compression to ignite. If it falls below a critical level (usually below 20-22 bar), the temperature of the compressed air will not be sufficient for auto-ignition.
The reasons for loss of compression can be serious: stuck or worn piston rings, burnt-out valves, a blown cylinder head gasket, or even a broken timing belt. In the latter case, the valves stop opening and closing at the right time, and the engine physically cannot start.
Compression is checked using a compression gauge screwed in instead of the injector. Low readings in one cylinder will indicate a local problem (valve, ring), and low readings in all will indicate general wear or a timing problem. It is also worth checking the timing marks, as the belt could have jumped one or two teeth, which would disrupt the valve timing.
Sometimes the reason for the lack of compression is “stuck” valves due to carbon deposits or breakdown of hydraulic compensators. In winter, the oil in hydraulic compensators may thicken, and they will not have time to adjust the gap, which is why the valve remains slightly open.
Effect of low temperatures and fuel quality
Winter is the harshest time for a diesel driver. The main problem is fuel waxing. As the temperature drops, paraffin crystals begin to form in diesel fuel, which clog the fuel filter and lines. The car may stall while driving or simply stop starting in the morning.
In addition, in a cold engine, the oil in the crankcase thickens, it is more difficult for the starter to crank the crankshaft, and it gains lower speed. For a diesel engine, it is the starter speed when starting that is critical. If there are not enough of them, the compression does not have time to increase, and the heat goes into the cylinder walls.
To avoid problems, it is necessary to use winter or arctic diesel fuel, and also add depressant additives. In emergency cases, you can warm up the fuel filter with a hair dryer or boiling water, but this must be done carefully so as not to damage the plastic elements.
Diesel fuel temperature limits:Summer: down to -5°C (beginning of waxing)
Winter: up to -25°C... -35°C
Arctic: down to -50°C and below
Is it possible to add gasoline to diesel for starting in cold weather?
Adding gasoline (up to 10-15%) really reduces the pour point of the fuel and makes starting easier. However, gasoline reduces the lubricity of a diesel engine, which is dangerous for the injection pump and injectors. Use this method only as a last resort and add a lubricant immediately after starting.
Why does a diesel engine start and stall immediately?
Most often this indicates a malfunctioning safety system or lack of fuel. Possible causes: a faulty engine stop valve, air in the system, a clogged diesel particulate filter (DPF), or a problem with the crankshaft position sensor. The ECU sees the error and turns off the engine.
How often do you need to change the fuel filter on a diesel engine?
The recommended interval is every 10-15 thousand kilometers or once a year, preferably before the onset of cold weather. For a diesel engine, a clean filter is a matter of engine survival; you cannot skimp on it.
What to do if the battery is dead and the diesel engine does not turn over?
A diesel engine needs a powerful starting current. “Lighting up” from a small car may not be enough. It is better to use a booster (starting device) or remove the battery and charge it with a stationary charger. Cranking the starter "pull" will only kill the battery.
To summarize, we can say that the successful start of a diesel engine depends on the health of three components: the starter (speed), compression (temperature) and fuel (quality and supply). Consistent testing of these systems allows in 90% of cases to find and eliminate the cause of the failure.