A fuel pressure regulator is an important part of a fuel pressure system. It ensures that the optimum amount of fuel pressure flows through your injector system. It can also dramatically improve your carburetor system’s fuel economy. A fuel pressure regulator functions by way of a spring attached to a diaphragm. The spring is calibrated by the manufacturer to resist just the right amount of pressure from the diaphragm, which raises with the fuel pressure. There is pressure on the other side of the spring from the intake manifold, which also adjusts the diaphragm. When manifold pressure is low, fuel pressure will be lower, when manifold pressure is high, fuel pressure will be higher as well.
Diaphragm adjustments due to pressure from both sides of the fuel pressure regulator allow the flow of fuel to be controlled accurately. Most fuel pressure regulars are located on the fuel rail or close to the injectors, but for return-less fuel systems, the pressure regulator is typically integrated into the fuel pump assembly. If that’s the case with your vehicle, then replacing your regulator if there’s something wrong with it would likely mean replacing the entire fuel pump. Fortunately, most vehicles have the fuel pressure regulator separate and easily accessible for replacement.
There is a valve at the diaphragm to let what exceeds the allowable amount flow into the return line. This action prevents the system from sending too much fuel to the injectors. It contributes greatly to economy, although not all systems have it. There are also bypass style regulators that function by way of a bypass valve that is operated by the spring. Bypass style regulators tend to cost around three times as much as traditional pressure regulators, but they are more efficient and more accurate.
How to Check Fuel Pressure
It’s easy to learn how to test fuel pressure in virtually any vehicle. In order to get a reading, you’ll need a fuel pressure gauge. You’ll also need a fuel pressure test kit. If you don’t own either one them, you can rent them from your nearby AutoZone or other auto parts store.
Read through the list of makes and models in your test kit booklet to find out which number tester you need for your specific vehicle. In the booklet you also might find the correct range of pressure for your make and model. If it’s not listed in the booklet, a quick Google search should tell you everything you need to know about the fuel pressure system in your vehicle.
If your vehicle doesn’t have a designated pressure test port located on the fuel rail, you’ll have to plug your tester in through the fuel line by detaching the line from the rail. You could also place the tester in between the fuel filter and its connecting line.
Attach the fuel pressure gauge to the tester and check to make sure all connections are secure. Once you’re ready, start the engine. Check the needle to see how many PSI it reads and compare it with the information you find online about your vehicle.
Signs that You Have a Bad Fuel Pressure Regulator
Here are some common fuel pressure regulator symptoms to look out for:
- The engine is hard to start or stalls out
- It’s idling rough or decelerates rough
- Black smoke comes out of the tailpipe
- Gas drips out of the tailpipe
- Your spark plugs are blackened
- Your dipstick smells like gas
- You’ve notice excessive fuel consumption
If your vehicle shows any of these symptoms, then you should run a regulator test as soon as possible.
Fuel Pressure Regulator Test
Checking your pressure regulator could be as simple as connecting a regulator gauge directly to the regulator if there is a designated testing port. Once connected, have someone start the engine. The gauge’s reading should increase by roughly 5 PSI. If it doesn’t, then you have a faulty pressure regulator. If the PSI decreases then that means that you have either a clogged fuel filter or a bad fuel pump. If there isn’t a designated port, then you’ll have to test the vacuum line.
Vacuum pressure originating from the engine allows the regulator to function properly. It helps control the pressure in the system, so if there is a leak then that could be all you need to fix. Testing the vacuum line while checking the fuel pressure simultaneously will give you a more comprehensive check.
In order to check for a leak in your vacuum line, simply replace the line with clear tubing, that way you’ll be able to see what’s happening in real time. Watch for gas in the line or anything else that shouldn’t be in there. You can get some clear tubing that matches the diameter of your line at a hardware store. You might also be able to use aquarium tubing if you have any.
What to Do if You Have a Bad Fuel Pressure Regulator
Depending on your specific make and model, you might have to replace the whole sending unit. But if all you need is the regulator, then you can buy a replacement at any major online marketplace for a low price, tax free depending on what state you live in. OEM (original equipment manufacturer) and aftermarket fuel regulators should function equally well more or less. Here are some of the best, highest value options available for online purchase now and direct links to the merchant’s website.
Aeromotive 13129 EFI
Holley 12-841 4.5-9 PSI Adjustable Bypass Billet
GENSSI Type S Adjustable Fuel pressure Regulator FPR Universal JDM Turbo
Standard Motor Products PR15T Fuel Pressure Regulator Kit
Top Street Performance JM1057BL 3/8″ NPT Blue/Clear Anodized Billet Fuel Pressure Regulator (5-12 PSI)