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When turning the key or pressing the start button in our vehicle, we’re relying on a complex harmony among air, spark, and fuel to generate power. And if something goes wrong with these three, our engine’s performance will most likely be dramatically affected. Among the list of possible things that can go wrong, low fuel pressure takes the cake in terms of “things you don’t want to experience.”
Regardless of what type of vehicle you have, from a daily driver to a highly modified machine, or even a Powerstroke, Duramax, or Cummins-powered diesel truck, learning what low fuel pressure means and how to address low fuel pressure is essential in keeping your machine healthy. Low fuel pressure leads to combustion issues in the chamber, increased EGTs, and can eventually lead to total engine failure.
In this article, we’ll take a close look at the symptoms, causes, diagnosis, and solutions for low fuel pressure, and get your engine back to proper working condition.
Low fuel pressure is a condition wherein the fuel pump is unable to supply fuel to the engine at a pressure level as desired by the manufacturer. Modern engines require high pressure to properly atomize the fuel in the combustion chamber. A drop in the fuel pressure below the calibrated level causes the engine to experience a lean air-to-fuel ratio. It results in poor performance, lack of power, difficulty in starting, and internal engine damage, especially when operating under a heavy load. This malfunction may trigger diagnostic trouble code P0087, among others.
Being able to recognize the symptoms of low fuel pressure promptly will save you a fortune on engine repairs. The signs that the delivery of fuel is inadequate allow you to troubleshoot and fix the issue before the lean air-fuel mixture burns the cylinder walls and pistons.
Below are the primary symptoms of low fuel pressure experienced by drivers.
The fuel injectors can’t atomize enough fuel to start the engine if the fuel pressure drops below a certain level, resulting in long crank times before the engine finally starts.
When accelerating, you are calling for richer air-fuel mixtures, which the engine can’t provide if the fuel pressure is too low. This causes the engine to hesitate, stutter, or stumble.
A lean air-fuel mixture doesn’t always combust completely and evenly, causing either random or cylinder-specific misfires and rough idle. The Check Engine Light may also appear, displaying a P0087 code (fuel rail or system pressure too low) as well.
Low pressure is most noticeable under full load. If you feel like your engine just can’t maintain speed on the highway, when climbing hills, or when towing behind your vehicle, it could be a sign of restricted fuel flow.
If the pressure drops below the minimum required to maintain idle speed, the engine will begin to sputter and die at idle or when coming to a stop.
There are a lot of potential reasons for low fuel pressure since an automobile fuel system consists of multiple parts. Therefore, many different things need to be functioning properly for your car to operate properly and have enough fuel pressure.
Here are the most likely causes of low fuel pressure for your case:
As the fuel filter becomes clogged with dirt, rust, and deposits, the restriction in the filter increases. The fuel pump has to work harder to push fuel through the filter. This results in reduced flow rate and pressure at the fuel rail.
Low fuel pressure can be produced if the fuel pump itself begins to fail or lose pumping strength. This happens as the fuel pump (either the low-pressure in-tank lift pump or the high-pressure engine-driven pump) wears out internally, loses its impeller clearance, or becomes overheated due to running the fuel tank low.
The fuel pressure regulator maintains the pressure in the fuel system by directing any excess fuel back to the tank. The internal diaphragm or spring in the regulator can stick open, allowing excessive fuel return and reducing pressure in the fuel rail.
If the injector remains open, the fuel pressure will drop rapidly when the engine is turned off. There is also a whiff of dark exhaust-manifold smoke when the fuel-injection pump delivers fuel to the leaking nozzle.
Crushed lines underneath the chassis, kinked hoses, or corroded passages in the fuel lines can cause a pressure drop in the fuel line, resulting in insufficient pressure at the fuel rail before the fuel reaches the engine bay.
Poor grounding, blown fuses in the fuel pump circuit, and faulty wiring and relays can cause the fuel pump to lose power supply or receive less power than required. It runs below its rated capacity.
Physical and Visual Inspection: Check the undercarriage of the vehicle for crushed fuel lines, rusted fittings, and signs of active fuel leaks. Check the smell of fuel around the engine, specifically at the rails and pressure regulator, for the presence of unburned fuel.
Check the Fuses: Check the fuses and relays associated with the fuel pump. Check the voltage at the fuel pump electrical connector with a voltmeter. The proper voltage with the key on should be at least 12 volts.
Mechanical Fuel Pressure Test: With an appropriate mechanical fuel pressure gauge, either on a Schrader valve or via an inline adapter, test the fuel pressure on the rail. With the motor running, observe the fuel pressure at idle, during acceleration, and under load. Compare the observed numbers to the specifications in the OEM service manual.
Fuel Pressure Holding Test: With the key on, prime the system so that the fuel pressure reaches its normal operating parameters. Then, turn the key off and observe the fuel pressure on the gauge. Pressure drop indicates a leaking injector, a faulty regulator, or a defective check valve in the fuel pump. Gradual pressure increase upon priming indicates a clogged fuel filter or restricted fuel line.
The most cost-effective solution for a clogged fuel filter is to replace it. It is recommended to replace it every 20,000 to 30,000 miles, depending on the manufacturer’s instructions.
If fuel is allowed to bleed back via the vacuum hose on a mechanical regulator or fails an electrical resistance test on an electric one, the pressure regulator should be replaced.
If the voltage is sufficient but the fuel pump can only produce less than the minimum psi recommended by the manufacturer, the fuel pump assembly must be replaced. During this procedure, the fuel tank should be cleaned to remove any dirt that could clog the new fuel pump.
Professional ultrasonic cleaning or injector replacement will eliminate the possibility of improper atomization and pressure loss due to faulty injectors.
While resolving abnormal fuel pressure loss restores proper delivery, heavy load operation or high boost plus restored fuel delivery can place enormous strain on engine components.
High cylinder pressures created during the restoration of fuel pressure can distort factory cylinder heads when engine components are weak or not properly torqued. It leads to serious engine damage and loss of engine power.
When working on highly modified fuel systems, high-pressure oil systems (HPOP), or internal engine components on gas and diesel engines, upgrading to higher tensile strength fasteners is a must.
The right hardware can withstand the extreme torque loads generated by big engines, high boost pressure, and cylinder pressures.
Industry-leading components from Tracktech Fasteners offer laboratory-tested and track-proven tensile strengths up to 240,000 PSI. This allows head studs, main studs, and high-pressure fuel system hardware to keep the engine block and heads properly clamped under extreme pressure and torque. Upgrading during engine or fuel system rebuilds is an advantage to ensure the quality and performance of the installed clamping hardware.
Avoiding the causes of fuel shortage is much easier than trying to deal with the consequences. It is vital to remember that a gas tank should not be lower than a quarter full, change fuel filters regularly, and use high-quality fuel with good detergents. Doing this will help to keep injectors clean and reduce the likelihood of high-pressure components failure while maintaining proper pressure throughout the engine’s lifetime.