Checking fuel pressure is very vital in diagnosing an engine performance issue. Depending on the application, it will take any where from a few moments to a few minutes to hook up a fuel pressure gauge. Most systems you can screw right into the fuel rail at the pressure test port while others you will have to tap into the line by removing the fuel line from the rail or even the line from the filter and installing a fuel pressure gauge in between the two in order to get an accurate reading. Click here to speak with a live mechanic if you need help.
Checking Fuel Pressure
Some fuel systems are only at 30 to 40 psi while others range in the 50 to 60 psi range or more. Once you know what your fuel pressure is at, you are going to want to go and look up the correct specifications for your vehicle to see if your fuel pressure falls within the factory specs. You can go to alldataDIY or another source to look up your specifications for your vehicle. If the pressure is low you will need to be sure that the filter and the high pressure line is not pinched or plugged up in any way. In addition, be sure that the pump has full battery voltage and a good ground before you replace it.
Types of fuel systems.
There are two types of fuel systems. Systems with a fuel return line back to the fuel tank and systems that do not use a fuel return line (returnless fuel system). The fuel systems that use fuel pressure regulator located on the fuel rail will have a return line back to the fuel tank. The ones that do not use a fuel pressure regulator on the fuel rail will not have a fuel return line going back to the fuel tank.
Some returnless fuel pressure systems use a fuel pump driver module or fuel pump control unit. This is a pulse width modulated signal that is sent to the fuel pump from the fuel pump driver module and engine computer to control the speed of the fuel pump which in turn will control the fuel pressure. The higher the pulse width signal, the higher the fuel pressure.
The fuel pressure between the two fuel systems will be different so be sure to know the correct specifications when checking fuel pressure.
Below are a few pictures of a fuel pressure gauge installed onto the fuel rail of a 1997 Chevy truck 1500 with a 5.7 liter engine. The fuel pressure test port is on the fuel rail on the drivers side of the engine. Simply attach the fuel pressure gauge to the fuel rail and turn the key on (you can start the engine if it runs) to take a fuel pressure reading.
And here is the fuel pressure reading after turning the key on and priming the system.
Which Fuel Pressure Tester should I use?
There are several different type of fuel pressure testers. If you want a good quality fuel pressure test kit that will do just about everything and will last for a life time, I would recommend to go with an OTC or a Snap On fuel pressure master kit. OTC Master Fuel Injection Kit will work just fine and you will save 200 bucks compared to the Snap on master fuel pressure kit.
A cheaper alternative would be one of the Actron fuel pressure gauges. They seem to be accurate, but they have their quirks. The seals and o rings need to be replaced regularly in order to prevent them from leaking fuel. So just careful. The good news is that it is cheap and easy to use. The Actron Fuel Pressure Tester is a good choice as it comes with the basic adapters. You can pick this up for about 44 bucks.
Here is a video of a fuel pump replacement on a 2005 Chevy Tahoe. This one came in on the hook because the fuel pump failed. We confirmed this by checking fuel pressure with a fuel pressure gauge and then by verifying power and ground going to the fuel pump.
Checking Fuel Pump current
Another good way to check to see if your fuel pump is bad is to check to see how much current your pump is pulling. You would measure current in Amps. You will need either a voltmeter that has an amp setting or a voltmeter that works with an amp clamp or a lab scope. I like using a Fluke 87 with an amp clamp for this job. It is a fantastic and extremely reliable voltmeter. Just clamp around the power wire going to the pump itself and start the vehicle. On some vehicles, you can remove the fuel pump relay and jumper the hot wire going to the relay and the pump should run. The amount of amps/current your pump will pull will depend on how much pressure your fuel pump should supply to the rail. A good rule of rule of thumb for this test is as follows: 14 to 15 psi 3 to 4 amps, 30 to 45 psi 4 to 7 amps, 45 to 50 psi 7 to 8 amps, 50 to 70 psi 8 to 12 amps. Click here if you would like to speak with a live auto mechanic.