A bad fuel pressure regulator will waste the gasoline you put in your car’s tank by letting too much fuel into the engine, or starve the engine by not providing it with enough fuel. In most cases, you will notice the engine is hard to start, idles rough and has poor performance. However, testing a fuel pressure regulator is an easy and useful skill you can incorporate into your car maintenance program.
Here we will deal with fuel regulators for Electronic Fuel Injection Systems (EFI), found on most cars. All you need is a fuel pressure gauge you can buy at most auto parts stores and some common tools you might already have in your toolbox.
1. Determine the type of fuel line disconnects your vehicle has and whether a test port-Schrader valve, similar to a tire air valve-is provided on the fuel line or rail, usually next to the fuel pressure regulator. This information will tell you whether you can hook the regulator gauge through the valve or the fuel line with the use of a T-shape adapter. You can find these adapters at most auto parts stores.
2. Relief the pressure on the fuel lines. The easiest way to do this is by depressing the needle in the center of the Schrader valve. Use a small screwdriver wrapped in a shop rag to catch the squirt of fuel. If a Schrader valve is not provided, remove the fuel pump fuse from the fuse box. Start the engine and let if idle for a few seconds until the fuel in the line is consumed and the engine stalls. Replace the fuse in the fuse box.
3. Screw the fuel pressure gauge extension hose on the Schrader valve or install it in the fuel inlet line with the necessary adapters.
4. Start the engine and make a note of the pressure indicated by the fuel pressure gauge and compare it with the low and high fuel pressure specifications for your vehicle. You will find these numbers in your vehicle service manual. Shut off the engine.
5. If the pressure readings indicate higher pressure than normal, the fuel pressure regulator is bad.
6. If gauge readings indicate lower pressure than normal, start the engine and block the return fuel line by pinching the hose with a pair of pliers using a shop rag to avoid damage to the fuel hose. Take a note of the fuel pressure gauge reading. If the reading goes to maximum fuel pump pressure, the regulator has failed and needs replacement. If the reading remains low, the fuel pump is not working properly.
If you cannot afford a fuel pressure regulator at this point, you can still rent one at most large auto parts stores. It is worth the effort since this is more than a simple troubleshooting procedure. It will help you find the real problem in the fuel system, but also save you money by improving fuel economy and engine performance on your car. And remember that your service manual will help you to locate specific components in your vehicle and let you know how to disconnect the fuel lines if necessary.