8 Common Fuel Pressure Regulator Failure Symptoms

Jerry Wilson
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How a Fuel Pressure Regulator Works

All internal combustion engines operate with varying fuel/air mixtures and cylinder pressures. A fuel pump dampens this pressure fluctuation by producing a constant pressure flow regardless of the engine load (throttle position).

The fuel is then sent through a hose along with an in-line fuel pressure regulator (or an electric fuel pump), which further maintains an even fuel pressure.

The fuel pressure regulator regulates the amount of fuel the engine gets, not its flow rate. The flow rate is determined by pump flow rating and the length of the fuel line on the engine.

What’s a fuel pressure regulator and why do you need it?

The fuel pressure regulator is typically installed at the end of your fuel line. It’s a small metal box with a diaphragm inside. The fuel enters the diaphragm chamber and the regulator maintains a steady pressure inside. This pressure then flows through a hose to the engine.

The diaphragm is actuated by a spring, which sends fuel to the engine. As fuel flows through the spring, it pushes on the diaphragm, so that the volume inside the chamber increases. As the volume increases, the pressure inside the chamber also increases. The diaphragm acts as a one-way valve. Fuel enters the chamber, but is never allowed to exit.

Symptoms of a Fuel Pressure Regulator Failure

The fuel pressure regulator often goes unnoticed until its malfunction causes problems with your diesel engine and fuel supply system. When your engine is running poorly or just won’t start, it’s easy to suspect the obvious and blame it on air, fuel, or ignition issues. Ignoring this situation, however, can lead to severe engine damage. A faulty or mis-adjusted fuel regulator can cause several different types of symptoms related to fuel pressure and fuel delivery. These include:

Reduced fuel economy • Reduced fuel pressure • Low cranking speed • Engine stumble • Engine misfires • Rough engine idle • Hesitation • Difficulty starting the engine

When these issues occur, the first step towards making a proper diagnosis is to evaluate the fuel pressure in the fuel rail. However, before you start troubleshooting your fuel pressure problems, make sure to rule out other problems that could be causing poor engine performance.

How to Replace a Fuel Pressure Regulator

The fuel pressure regulator is normally found on modern vehicles between the fuel tank and fuel injection system. But its function, which is to maintain a consistent fuel pressure, is very important. When a fuel pressure regulator has a problem, it will cause a variety of warning signs and symptoms that you’ll need to notice so you can address the problem quickly.

A fuel pressure regulator works by controlling the number of times the fuel injectors spray each minute. Fuel injectors are located within each cylinder of the engine. When more fuel is needed, the fuel injectors spray more times per minute (even at idle.) This is why diesel engines are less responsive at idle.

The fuel injectors at idle spray less than at full throttle, when they spray more times each minute. If the fuel pressure regulator is faulty, the fuel injectors spray too many times, and when they do, they spray more than the engine needs. The intake manifold is left with fuel dripping where it’s not needed.

This causes poor performance, poor fuel efficiency, and other problems.


Know the common signs that your RVs fuel pressure regulator has failed, and you’ll be better prepared to find the problem. Then, in turn, you can get it back on the road.