7 Symptoms of Low Fuel Pressure (And How to Test for It)
Having trouble starting or running your car? You may have low fuel pressure. Internal combustion engines need a precise amount of air and fuel to run properly. If your vehicle has low fuel pressure, your engine may not be getting enough fuel to run properly.
Symptoms of Low Fuel Pressure
Here are some common problems you may experience if your vehicle has low fuel pressure.
1) Check Engine Light
The check engine light often comes on when fuel pressure drops lower than expected. A common low fuel pressure code is P0087, or “Fuel Rail/System Pressure Too Low”.
Scanning for this code can be extremely helpful in the diagnostic process. P0087 indicates that there is a problem somewhere in the fuel system. If this is the only code, there is no need to do a smoke test to check for air leaks, for example.
2) Vehicle won’t start
A vehicle with low fuel pressure may start normally, but not start. When you turn the key, the ignition tells the ECU to send power to the starter solenoid. The starter solenoid activates an electric starter motor, which turns the engine over via small gears.
Fuel is injected during this process, but no fuel is used to turn the engine over until the car is fully started, which is the point at which the engine will turn over on its own.
3) Problems keeping the vehicle running
A car with low fuel pressure may start and idle fine, but when you add gas, it may run rough or stall. It takes much more fuel to get the car moving than it does to keep it idling.
4) The car suddenly breaks down
If your car doesn’t have enough fuel, the engine will stall. This can happen if the fuel pressure drops too low or if the fuel pump fails completely. There are many issues that can cause a car to stall, but the most common cause is a problem with the fuel supply.
5) Rough Idling
If the air/fuel mixture is not right, your car will have difficulty maintaining a smooth idle. A rough idle can be caused by a variety of reasons, including air leaks and ignition issues.
6) Loss of Power
A lean idle is good for fuel economy, but it doesn’t help performance-wise. If fuel pressure is low, the ECU will detect this and take protective measures to prevent engine damage. This can cause a loss of power and the vehicle to go into limp mode.
7) Knock or detonation
The mixture is precisely controlled in real time by the ECU. When the air/fuel mixture becomes very lean, the engine runs hotter. A hot engine combined with an improper fuel mixture can cause engine knocking or detonation.
Engine knocking is when fuel burns in the combustion chamber before it should. This is usually caused by a timing issue, but knocking issues can also occur with engines that run very lean. Why is fuel pressure low?
1) Fuel pump failure
A defective fuel pump may not be able to provide enough fuel pressure to the engine, especially when it is under load. If the fuel pump fails, you may notice that your car starts to sputter, jerk, or hesitate when adding gas.
Newer direct injection vehicles have two fuel pumps: a standard fuel pump and a high-pressure fuel pump. Extremely high pressure is required to inject fuel directly into the combustion chamber. The high pressure fuel pump is used to deliver fuel pressure to the injectors.
2) Clogged Fuel System (Faulty Fuel Filter)
A clog in the fuel system can cause insufficient fuel pressure to reach the fuel lines. A common cause of a clogged fuel system is sediment or deposits from bad gasoline.
Over time, these deposits can build up in the fuel filter and restrict fuel flow. If you haven’t changed your fuel filter in over 100,000 miles, you should consider doing so.
3) High G Corners
If you like to drive your car like a race car, you may run out of fuel in high G corners at full throttle. This is especially common in vehicles that are not designed for the race track.
When you turn the steering wheel too hard, the fuel in the tank can get away from the fuel pump’s fuel pickup and spill out to the side. When this happens, air is drawn into the fuel system and the engine temporarily loses fuel.
To prevent this from happening, make sure you have at least a quarter tank of fuel on your track days. Some vehicles may run out of fuel when only half a tank is full. This varies from car to car and depends on the design of the fuel system.
4) Running out of gas (high fuel consumption)
A low gasoline level will cause similar problems as cornering at high speeds. When there is not enough fuel in the tank, the fuel pump will start sucking in air instead of fuel. When this happens, the engine will stop delivering fuel, causing a temporary drop in fuel pressure. For most engines, it’s a bad idea to regularly run on less than a quarter tank of fuel. That’s because the fuel pump is both cooled and lubricated by the fuel inside it. If the fuel level is too low for an extended period of time, the fuel pump can burn out prematurely.
5) Fuel Leaks (Car Smell)
If you have a significant fuel leak, you may experience a drop in fuel pressure. Fuel leaks can be easy to spot because you’ll smell raw gasoline somewhere in the car. Your nose often leads you to the root.
Fuel leaks are very dangerous and must be repaired immediately. Many car fires are caused by fuel leaks. When a vehicle fire occurs, you have very little time to react and escape from the car. This is especially dangerous when driving at high speeds or in heavy traffic. Can you test the fuel pressure?
You can test the fuel pressure with a fuel pressure tester kit. Many vehicles are equipped with a Schrader valve (similar to the valves found in car and bicycle tires) that you can connect a fuel pressure gauge to to monitor the fuel pressure.
For this test, turn the key to the “ON” position. The engine does not necessarily have to be running, but the fuel pump must be on. When you turn the key to the “ON” position, you will hear the fuel pump engage. It usually sounds like a quiet hum that lasts for a few seconds. Some fuel pumps engage when the driver’s door is opened rather than when the key is turned.
The factory service manual and many repair manuals will tell you exactly how to test fuel pressure for your specific vehicle and what the target fuel pressure range is. Target fuel pressure is usually in the range of 30-60 PSI. If you don’t have access to a repair manual, you may also be able to find this information in online forums or Facebook groups. Make sure the original post is for the same year, make and model, as specifications can vary even within the same manufacturer.