How To Fuel Pressure Regulator Troubleshooting

How To Fuel Pressure Regulator Troubleshooting


Whether your car is modified or not, fuel problems can be a headache to handle. Although there are many cases when your fuel pump dies, or there’s not enough fuel, it’s often easy to figure out. Upgrade your fuel pump or replace the worn fuel component to restore fuel. But what happens when your car has too much fuel? When this occurs, chances are you’ll want to learn the in’s and out’s on fuel pressure regulator troubleshooting.

When you need to know the basics to fuel pressure regulator troubleshooting, this guide can help. Today we’ll be going over the vital points to the fuel pressure regulator in your vehicle, and showing you what the basics are.

Fuel pressure regulator troubleshooting 101

What is a fuel pressure regulator – The FPR or the fuel pressure regulator is a valve that maintains an even pressure in your fuel rail. Ideally the fuel pressure regulator keeps pressure even, so that your fuel injectors fire properly and deliver the right amount of fuel.
fuel pressure regulator troubleshooting

When you want to learn fuel pressure regulator troubleshooting, you’ll be best served by understanding what the regulator is. It’s a diaphragm that operates on a vacuum activated signal, and it opens or closes to maintain even pressure.

How does the fuel pressure regulator fail – Although the regulator is made to do a specific and very important job, it can fail. By design however, there’s usually only one way that an FPR can fail. When the internal seal and diaphragm fails in your regulator, you may have excessive fuel pressure in your rail or fuel may leak out of the unit.

These failures can occur when the internals of your regulator goes bad, or you use a fuel or fuel additive that is corrosive or not compatible with your regulator.

Differences between fuel pressure regulators – Aftermarket fuel pressure regulators are shiny and made from high quality components, but their job is the same as factory FPR units. Units like the DeatschWerks DWR1000 fuel pressure regulator is designed as the ultimate FPR.

fuel pressure regulator troubleshooting 1

Fuel Pressure is too high – You’ll need to undergo fuel pressure regulator troubleshooting when you’ve found that your fuel pressure is too high. Excessive fuel pressure can cause a variety of different problems, here’s a look at just some of them below.

  • Engine idle is erratic – Excessive fuel pressure will cause your engine to idle higher than normal.
  • Bad gas mileage – More gas is being delivered and your injectors can’t reduce the pressure. This wastes gas and causes your engine to run poorly.
  • Poor engine performance – Too much fuel means that your engine is wasting gas and not achieving the stoichmetric mixture required.
  • Excessive exhaust gas temperatures – When your car runs rich, your exhaust gases become hotter. Left uncorrected your excessively high exhaust gas temperatures will cause your catalytic converter to fail.

Because your injectors cannot regulate how much fuel is being delivered when your fuel pressure is too high, your car will run rich. This means it will be using too much fuel, instead of the right amount.

When fuel pressure is too high

Having too much fuel pressure in your rail can occur from a variety of problems. One of the most common problems arises when you have upgraded your fuel pump. Upgrades like a Walbro Fuel Pump will ratchet up the pressure, and your poor factory fuel pressure regulator isn’t able to crank down the pressure.

fuel pressure regulator troubleshooting 2

This is commonly why most people who upgrade their fuel system must also upgrade their fuel lines and fuel pressure regulator. The other failure that causes your fuel pressure to skyrocket is when your regulator goes bad or seizes.

Why is my fuel pressure too high?

Don’t forget that in essence fuel pressure regulators are nothing more than metered restrictions in your fuel system. Much like your finger over a water hose, as you hold down your finger over the opening the water pressure steadily increases.

When your fuel pressure is too high, you’ve got one of two problems with your car. Either your regulator is too small for your fuel flow, or there’s a serious restriction in your fuel line. We’ve covered the scenario when there’s too much fuel flow for your regulator, common for fuel pump upgrades.

When your regulator seizes, it’s an issue that falls under the latter category. Because the fuel cannot escape your rail, the pressure continues to climb which is not the basis of an efficient vehicle. If you’ve gone through fuel pressure regulator troubleshooting and found that your regulator is good but your pressure is still too high, there may be another restriction in your fuel system.

Restrictions in fuel pressure regulator troubleshooting

If you’ve found that your regulator checks out, your pump should be fine, then it’s a problem with a restriction in your lines. This restriction can be anything from your return hose being too small, to improper fittings or restrictive fittings inside your fuel system.

Remember that if your fuel system has a restriction some place after your fuel pressure regulator, it’s the same as having a failed regulator itself. Don’t forget that just because your FPR can keep up with your fuel flow, doesn’t mean there isn’t a restriction in the return line doesn’t allow the fuel to flow back to your tank.

Our friends at Fuellab investigated this in a recent test, where they took apart the fuel pump assembly in a vehicle.


They took apart the fuel pump assembly, which is shown to the left.

You’ll see the plastic return line and the gas level floater clearly shown. Fuellab took apart the assembly to find that the restriction in question was the fuel return line.

As you’ll notice in the fuel pump assembly image below, Fuellab took apart the fuel return line and drilled out the opening to allow for increased fuel flow.

FL-Photo-2This modification got the fuel pressure down to the point where the tuner could handle the tuning.

When you find that your fuel pressure is far too high in your rail, proper fuel pressure regulator troubleshooting is required.

Different fuel pump assemblies may use different styles of fuel line return. Many assemblies like the one shown above have smaller orifices and step down fittings in it that can reduce the flow your FPR requires.

When fuel pressure is too low

When you don’t have enough fuel pressure, more than likely it’s a problem with your supply. Either you need to test your fuel pump, or see if your aftermarket fuel pressure regulator is installed incorrectly. There are many cases we’ve seen where just a few steps in fuel pressure regulator troubleshooting can uncover the obviously incorrectly installed FPR.

If your fuel pressure regulator checks out, then it’s obviously a flow issue with your fuel pump. If your pump has recently been installed, make sure to check the line to see if there’s any fuel being delivered at all to your FPR. It’s one of the first things to check when your car won’t start after all.

Installing or upgrading your fuel pump should solve the issue of low fuel pressure in your rail. If your pump checks out however, there is a small chance that there’s something preventing your regulator from seating fully. This could cause more fuel to flow back into your tank than what your FPR wants, which will lower your fuel pressure.

When undertaking your own fuel pressure regulator troubleshooting, make sure to check the important components and always check for restrictions. Have any questions about our guide on troubleshooting your FPR? Leave us a comment below and let us know!