7 Symptoms of Low Fuel Pressure (And How to Test It)

Are you having issues starting or running your vehicle? You may have low fuel pressure.

Combustion engines need a precise amount of air and fuel to run properly. When your vehicle has low fuel pressure, your engine probably won’t have enough fuel to run right.

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Symptoms of Low Fuel Pressure

Here are some common problems you might experience if your vehicle has low fuel pressure.

1) Check Engine Light

The check engine light often illuminates when your fuel pressure drops lower than expected. A common code for low fuel pressure is P0087, or “Fuel Rail/System Pressure Too Low”.

Scanning for this code is pretty helpful in the diagnostic process. P0087 tells you that the problem lies somewhere in the fuel system. If this is your only code, there is no need to do a smoke test to check for air leaks, for instance.

2) Can’t Start the Vehicle

A vehicle with low fuel pressure should crank easily, but may not start. When you turn the key, the ignition tells the ECU to send power to the starter solenoid. The starter solenoid activates the electric starter motor which spins the engine via a small gear.

Fuel is injected during this process, but it is not being used to spin the engine until the car fully starts. That’s the point where the engine will turn under its own power.

3) Trouble Keeping the Vehicle Running

A car with low fuel pressure may start and idle fine, but run rough or hesitate any time you give it more gas. It takes much more fuel to get the car moving than it does to maintain idle.

4) Car Stalls

If your car doesn’t get enough fuel, the engine will stall. This can happen when the fuel pressure drops extremely low, or if the fuel pump cuts out entirely. There are many problems that can make your car stall, but fueling issues are common causes.

5) Rough Idle

Whenever the air fuel mixture is off, your car will have a hard time maintaining a smooth idle. Rough idle can be caused by a number of other reasons, including air leaks or issues with the timing.

6) Power Loss

Although running lean is great for fuel economy, it won’t do you favors in the power department. If your fuel pressure is low, your ECU will see this and take protective measures to prevent engine damage. This could result in power loss and even the vehicle entering limp mode.

7) Knock or Detonation

Air fuel mixtures are precisely regulated by the ECU in real time. If the air fuel mixture becomes very lean, the engine will run hotter. The combination of the hotter engine and incorrect fuel mixture could cause knock or detonation inside the engine.

Engine knock is when fuel burns inside the combustion chamber before it is supposed to. This commonly happens due to timing issues, but it is not out of the question for an engine that runs very lean to have issues with knock as well.

Why Is My Fuel Pressure Low?

1) Bad Fuel Pump

A bad fuel pump won’t be able to deliver adequate fuel pressure to the engine, particularly under load. When your fuel pump is failing, you might notice the car start to sputter, stumble, or hesitate when you give it more gas.

Newer vehicles with direct injection have two fuel pumps – a standard fuel pump and a high pressure fuel pump. It takes a very high pressure to inject fuel directly into the combustion chamber. The high pressure fuel pump is used to drive the fuel pressure to the injectors.

2) Obstruction in the Fuel System

If there is an obstruction in the fuel system, it may prevent adequate fuel pressure from reaching the fuel rail. Common sources of obstructions in the fuel system are sediments and deposits from bad gasoline.

After a while, these deposits build up in the fuel filter and could block the fuel flow. If you haven’t changed your fuel filter in over 100,000 miles, you may want to consider doing this.

3) High G Corners

If you like to drive your car like a race car, you may experience fuel starvation in high G corners when you’re full throttle. This is especially common on vehicles that aren’t designed for the race track.

When you’re taking a fast corner, the fuel in your fuel tank may slosh to the side away from the fuel pump’s fuel pickup. When this happens, air is sucked into the fuel system and the engine is briefly starved of fuel.

To prevent this from happening, make sure you maintain at least a quarter tank of fuel at a track day. Some vehicles may experience fuel starvation on even a half tank of fuel. This will vary from car to car depending on how the fuel system is designed.

4) Out of Gas

Running low on gas will cause similar issues to taking fast corners. You don’t have enough fuel in the tank, and the fuel pump starts to pull in air instead of fuel. When this happens, your fuel pressure will drop momentarily as your engine starves of fuel.

It’s not great for most engines to routinely run less than a quarter tank of fuel. This is because fuel pumps are both cooled and lubricated by the fuel they sit in. When the fuel level drops too low for prolonged periods of time, the fuel pump could burn out prematurely.

5) Fuel Leak

If you have a significant fuel leak, you may experience a drop in fuel pressure. Fuel leaks are sometimes easy to find because you will smell raw gasoline somewhere around the car. Many times your nose will lead you to the source.

Fuel leaks are very dangerous and must be fixed immediately. Many car fires are started by fuel leaks. Once a car fire starts, you have very little time to react and exit the car. This is particularly dangerous if you are moving at a high speed or driving in heavy traffic.

Can You Test Fuel Pressure?

You can test fuel pressure using a fuel pressure tester kit. Many vehicles have a Schrader valve (similar to what you’d find on a car or bicycle tire) that will allow you to hook up a fuel pressure tester to monitor the fuel pressure.

Turn the key to the ON position for this test. The engine does not necessarily have to be running, but the fuel pump will need to be powered on. When you turn the key to the ON position, you should hear the fuel pump activate. It usually sounds like a quiet hum that lasts for a few seconds. Some fuel pumps are activated when you open the driver’s door, not when the key is turned.

Factory service manuals and many repair manuals will tell you the exact process for how to test the fuel pressure on your specific vehicle, as well as the target fuel pressure range. The fuel pressure target is usually somewhere in the 30-60 PSI range.

If you don’t have access to a repair manual, online forums and Facebook groups may have this information as well. Make sure the original post is about the same year, make, and model, as there will be variance in technical data even within the same manufacturer.

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Sean

Sean is an avid car enthusiast who maintains his own personal fleet of vehicles and wants to help others do the same. He has received many hours of professional driving instruction, is a member of the SCCA, and takes the art of driving seriously. Thoughtful, skilled driving has the potential to save many lives. Sean can often be found at the race track, autocross course, or hillclimb event.