Regan Brown
Diesel fuel injection pumps are designed to rely on the fuel being non-compressible. However, air locks can occur in the fuel delivery line or when air enters from the tank. This can be caused by a variety of factors, including allowing the fuel tank to run dry, changing a fuel filter, or having leaky fuel lines. While vapor lock is rare in modern fuel systems, diesel engines can still experience this issue, especially if the vehicle is in traffic or parked after being stopped while hot. To address air locks and vapor lock, modern diesel injection systems have self-bleeding electric pumps, and there are also manual solutions such as turning the engine over with a starter motor.
Characteristics and Values related to diesel fuel injection pump lock-up
| Characteristics | Values |
|---|---|
| Cause of lock-up | Air intrusion, fuel filter change, leaky fuel lines, or running out of fuel |
| Solution | Turn the engine over using the starter motor or bleed the fuel system |
| Prevention | Use modern diesel injection systems with self-bleeding electric pumps |
| Torque Value | 15 to 20 nm [132 to 177 in-lb] for Tier 2/Stage II Industrial emission level engines |
| Fuel Pump Lock Timing Screw | Should be tightened with a washer under the screw |
| Engine Timing Pin | Should be disengaged before rotating the crankshaft |
| Final Torque Specification | Bosch VE pump with M12 drive nut: 48 ft-lb; Bosch with M14-1.5 nut: 60 ft-lb |
| Fuel Inlet Line | Tighten when fuel flows freely from the fuel inlet line to the injection pump |
| Fuel Return Line | Tighten when fuel flows from the return line or overflow fitting |
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What You'll Learn
Air intrusion can cause a diesel fuel injection pump to lock up
Air intrusion can cause the diesel fuel injection pump to lock up because standard diesel fuel injection pumps rely on the fuel being non-compressible. When air leaks into the fuel delivery line or enters from the tank, it can cause an air lock, which disrupts the operation of the fuel pump and can result in a transient loss of power or complete stalling of the engine.
To eliminate air locks, the engine needs to be turned over for some time using a starter motor, or the fuel system needs to be bled. Modern diesel injection systems have self-bleeding electric pumps that eliminate this problem.
Additionally, air intrusion can lead to fuel drain back, which occurs when the engine is shut off and can cause starting issues. While fuel drain back will not cause issues while the engine is running, it is often confused with air intrusion due to their related nature.
To prevent air intrusion and potential diesel fuel injection pump lock-up, it is important to regularly maintain and inspect the fuel system, ensuring that the fuel tank is not run dry and that all fuel lines and connections are secure and leak-free.
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Bleeding the fuel system can prevent lock up
To bleed the air from the fuel system, first, ensure that you have determined how air entered the fuel system so that air does not re-enter the system after completing the bleeding process. Familiarize yourself with the engine and identify the key components of its diesel fuel system, including the fuel tank, fuel lines, fuel filter, and fuel injectors. Review the engine's fuel system layout and connections. Next, work with the fuel filter by turning off the engine and removing the ignition key from the cylinder. Locate the fuel filter and determine whether it has a built-in bleeder screw. If the fuel filter has a bleeder screw, position a clean rag or towel beneath the bleeder screw to catch any fuel spills. Use a wrench or bleeder screw key to loosen the screw slowly in a counterclockwise direction. If the fuel filter does not have a bleeder screw, you may need to bleed the fuel system at the fuel injectors.
Locate the engine's fuel injectors, typically connected to the fuel lines. Use a wrench or socket set to loosen the fuel line connection. Crank the engine for a few seconds to allow the air to escape, being cautious of fuel spills. Tighten the fuel line connection when you observe a steady fuel flow without air bubbles. Repeat this process for each cylinder and fuel injector, working in order from the cylinder closest to the fuel pump to the one farthest from the fuel pump. After bleeding the fuel system, try to start the engine. If the engine starts, allow it to idle for a few minutes while looking for signs of rough idle or reduced power.
Close the bleed plugs after all air is removed from the fuel tank, filters, settlement bulb, and fuel pump (only one at a time, working through all bleed screws, beginning closest to the tank and ending at the nozzles if necessary). Try the engine; if it doesn't start or runs poorly, you may have to bleed the injection line. Loosen the injection lines at the injectors about one turn. Usually, it is enough to bleed just half of the lines at a time. Crank the engine until all air is forced out and fuel is present. Run the engine until it runs smoothly. This will bleed the other injectors. No attempt should be made to service the injection pump or nozzles.
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Fuel tank running dry can cause air locks
A fuel tank running dry can cause air locks. Airlocks occur when air enters the fuel system and keeps the diesel fuel from reaching the injectors. This happens when air leaks into the fuel delivery line or enters from the tank. A fuel tank running dry is one of the common causes of air locks, along with changing a fuel filter or leaky fuel lines.
A diesel fuel injection pump relies on the fuel being non-compressible. When an air lock occurs, a bubble gets stuck in the system, and the engine cannot pass fuel through it. This can lead to difficulty starting the engine, reduced engine power after starting, and, in severe cases, the inability to start the engine.
A fuel tank running dry will almost certainly result in an air lock. However, this issue can be resolved by ensuring the fuel tank does not run dry. Leaks in the fuel lines may also cause sporadic air locks and reduced engine power, and this issue can be addressed by repairing the problematic parts.
Airlocks can also be caused by air in the fuel and improper filter-changing procedures. These airlocks can be addressed by bleeding and properly priming the fuel lines, which can be time-consuming. Modern diesel injection systems have self-bleeding electric pumps that eliminate the air lock problem.
Vapor lock is a problem caused by liquid fuel changing state to vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Vapor lock is rare in modern fuel systems, as most modern engines are equipped with fuel injection and have an electric submersible fuel pump in the fuel tank.
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Fuel filter changes can cause air locks
While diesel engines almost never suffer from vapor lock, they are more susceptible to air locks in their fuel lines. This is because standard diesel fuel injection pumps rely on the fuel being non-compressible. Air locks are caused by air leaking into the fuel delivery line or entering the tank. Common causes include the fuel tank being allowed to run dry, changing a fuel filter, or leaky fuel lines.
Changing the fuel filter can introduce air into the fuel system, causing air locks. This is because the new fuel filter needs to be filled with fuel and later topped off to limit the air introduced into the fuel lines. Therefore, it is important to prime the fuel filter correctly during installation. Failure to do so can result in airlocks, which can cause difficulty starting the engine, reduced engine power after starting, and, in severe cases, the inability to start the engine.
To eliminate airlocks, the fuel system must be bled to remove the air manually, or the ignition can be used to prime the fuel system. Modern diesel injection systems have self-bleeding electric pumps that eliminate the air lock problem. Additionally, fuel systems such as AirDog® can handle air introduced by error and virtually eliminate airlock issues. These systems use a water separator to eliminate moisture and particulates, a Fuel Preporator to remove air from the fuel, and integrated pumps to send pure diesel fuel to the engine at a regulated positive pressure.
It is important to note that air and water in diesel fuel reduce engine performance and fuel economy and can damage critical engine parts over time. Therefore, it is recommended to use a fuel system that effectively removes air and moisture before the fuel enters the engine, such as the AirDog® fuel system. This will help achieve peak engine performance and avoid the issues caused by air locks.
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Leaky fuel lines can cause air locks
Diesel engines almost never suffer from vapor lock, where liquid fuel changes state to vapour while still in the fuel delivery system, disrupting the operation of the fuel pump. However, diesel engine fuel systems are more susceptible to air locks in their fuel lines. Air locks are caused by air leaking into the fuel delivery line or entering from the tank. Common causes include the fuel tank being allowed to run dry, changing a fuel filter, or leaky fuel lines.
A fuel leak can become a problem without prior warning, causing a fuel pressure drop, compromising the operation of the fuel system. Leaks in your fuel lines may also cause sporadic airlocks and reduced engine power. This requires a repair of the faulty parts.
Modern diesel injection systems have self-bleeding electric pumps that eliminate the air lock problem. Additionally, AirDog® fuel systems are very effective at addressing airlock issues. The AirDog® fuel system first sends the fuel through a water separator that eliminates moisture and particulates. Then, the fuel passes through the AirDog® Fuel Preporator, which removes air from the fuel. Finally, fuel pumps integrated into the AirDog® fuel system send the pure diesel fuel to the engine at a regulated positive pressure.
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Frequently asked questions
A fuel injection pump lock is when the liquid fuel changes state to vapour while still in the fuel delivery system, disrupting the operation of the fuel pump.
There are several reasons why your diesel fuel injection pump may be locking up. One reason could be air intrusion, which occurs when air leaks into the fuel delivery line or enters from the tank. Another reason could be that the fuel tank has been allowed to run dry, or there could be an issue with the fuel filter or leaky fuel lines.
To prevent your diesel fuel injection pump from locking up, it is important to regularly check for any leaks or issues with your fuel delivery line and tank. Ensure that your fuel tank is always filled to prevent it from running dry.
If your diesel fuel injection pump is locked up, you may experience issues such as loss of power, complete stalling, or difficulty restarting the engine.
If your diesel fuel injection pump is locked up, you may need to seek professional help to diagnose and resolve the issue. Some possible solutions include turning the engine over using the starter motor or bleeding the fuel system.
