How to Test a Fuel Pressure Regulator - AxleAddict - A community of car lovers, enthusiasts, and mechanics sharing our auto advice
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How to Test a Fuel Pressure Regulator

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Fuel pressure regulator, injectors and fuel rail.

Fuel pressure regulator, injectors and fuel rail.

If you learn how to test a fuel pressure regulator (FPR), you may save some money on repairs and get your vehicle going sooner. A fuel pressure regulator commonly fails in one of two ways:

  • When it fails to hold pressure, it provides too little fuel to the engine, causing a lean mixture (low pressure) condition.
  • When the FPR gets stuck and builds up more pressure then it should, it'll cause the injectors to deliver too much fuel, causing a rich mixture (high pressure) condition.

A worn out spring or valve, a leaking diaphragm or lack of vacuum to the pressure regulator may cause these conditions.

Common bad FPR symptoms include:

  • hard starting
  • running rough
  • misfiring
  • stalling
  • no-start condition
  • hesitation

However, other worn out or failed components—like the fuel filter, fuel pump, and automatic transmission issues—can also cause similar symptoms to those of a failed pressure regulator. So you need a way to troubleshoot the regulator in your vehicle whenever you suspect a malfunction.

Here, you'll find a couple of tests you can do at home with the use of a fuel pressure gauge, a fairly inexpensive tool. If you don't have this gauge, you may buy one from your local store or online.

Also, it's a good idea to have the repair manual for your particular vehicle make and model. The manual comes with specifications for your particular fuel system, and many other systems, including particular tests for it, if applicable.

Haynes manuals are an inexpensive, aftermarket good choice. They come with step-by-step procedures, illustrations and systems descriptions for many troubleshooting, maintenance and parts replacement projects you can do at home.

Index

I. Checking for FPR Fuel Leaks

II. How to Check a Fuel Pressure Regulator

REMINDER - Fuel Filter Replacement

III. Testing for Maximum Pressure

WARNING - Fuel Pressure

Quiz - Test Your Knowledge of FPRs

Look around the end of the fuel rail to find the fuel pressure regulator.

Look around the end of the fuel rail to find the fuel pressure regulator.

I. Checking for FPR Fuel Leaks

The easiest way to test an FPR is with the use of a fuel pressure gauge. But first, you'll start your tests with a quick preliminary check:

1. Open the hood and locate the fuel pressure regulator on one end of the fuel rail. This rail holds the fuel injectors in place. A standard regulator is a small metallic cylinder with a thin vacuum hose connected on top. Also, you may see an incoming fuel line and a return fuel line connected to it, depending on your particular configuration.

Note: the tendency on newer vehicle models is to place the fuel pressure regulator inside the fuel tank as part of the fuel pump assembly. So you won't find the regulator or a return fuel line on these models. The computer helps maintain pressure along with the pressure regulator.

2. Check the vacuum hose for a tight connection. A loose hose will prevent the regulator from working properly. Also, check the hose for damage and wear. Then disconnect the vacuum line from the regulator.

3. If you see any signs of fuel in the vacuum line, the diaphragm inside the pressure regulator has a leak and you need to replace the regulator. Otherwise, continue with the rest of this test.

Note: try to do this test right after you've taken you car for a ride on the highway which helps reveal small fuel leaks.

II. How to Check a Fuel Pressure Regulator

The order in which you perform the following tests for your particular system (key on, engine off; engine running; or just engine running, may vary. Consult your repair manual.

1. Locate the Schrader valve. Most modern fuel injection systems come equipped with a Schrader or test valve located on the fuel rail. The valve is similar to the air valve on your tires.

2. Connect your fuel pressure gauge to the Schrader valve or test port. If your system doesn't have this valve or has an older fuel system, check the repair manual for your particular vehicle model for the best way to connect the gauge to the system.

Note: if there's no test port or you don't have the correct adapter, remove the test port valve and connect the gauge directly; or disconnect the fuel inlet line and connect a T-adapter. Then reconnect the fuel line and connect the gauge to the T-adapter.

3. Then find the fuel system pressure specification for your particular model with the engine running and off. Look up this number in your car repair manual.

4. Start the engine and let it idle (or have an assistant crank the engine for a few seconds, if the engine doesn't start). Then turn off the engine.

5. Observe the fuel pressure gauge while the engine runs and after shutting off the engine. Fuel pressure should hold to specs, while the engine is running, and after turning off the engine. With the engine off, pressure should hold for about 5 minutes. If necessary, consult your repair manual.

Note: While conducting this test, also remove the vacuum line while the engine is running. It should cause the pressure to rise. Otherwise, there's a problem with the FPR.

6. Make a note of the pressure gauge reading.

7. Ask an assistant to turn the ignition key to the On position (without starting the engine) for 5 seconds, and then to turn it off. Repeat this step at least 5 times to make sure fuel pressure is consistent; otherwise, the FPR might be sticking.

8. Compare your readings to specification in your repair manual.

  • If your gauge reading is lower than the specification while the engine is running (pressure goes down quickly or after a few minutes, or doesn't build up), possible culprits could be: a leaking fuel injector, the fuel pump (worn out pump or not receiving full voltage), fuel filter (restricted or clogged), anti-drain valve (failed—draining fuel back into the fuel tank) on the fuel pump assembly, or a bad FPR. Continue reading.
  • If fuel pressure begins to drop soon after shutting off the engine, you probably have a leaking injector, a leaking anti-drain valve in the fuel pump assembly or problems with the FPR itself.
  • When you detect low pressure, and you have not changed the fuel filter in more than a year (or at the interval suggested in your car owner's manual), it is a good idea to replace the filter, and repeat the test again. A clogged or partially clogged filter may be your problem. After installing a new fuel filter, if pressure is still too low or system loses pressures after shutting off the engine, head over to the next section Testing for Maximum Pressure.
  • If your gauge reading goes above specification and you know the vacuum line is in good condition, properly connected and not clogged, most likely your FPR is to blame.

If your fuel pressure regulator passed your tests, but you still suspect a problem with the fuel delivery system, check system volume. A restriction in the system or worn out pump will affect volume delivery and pressure under certain conditions.

Also, you may want to test vacuum supply, if your FPR operates through a vacuum line. You can use a vacuum gauge to check the line and make make sure there are no restrictions.

III. Testing for Maximum Pressure

You want to do this test if your previous test showed low fuel system pressure after shutting off the engine. The test may help locate the point of failure, provided your fuel filter is not clogged or due for replacement.

This particular test is similar to the previous. You'll use your fuel pressure gauge. But this time, you'll try to locate the likely source for low fuel system pressure.

1. Connect the fuel pressure gauge to the fuel system as you did in the previous section.

2. Now, place a rag over the fuel incoming line (hose) and another rag over the fuel return line (hose). If you need more help to locate these lines, consult the repair manual for your particular vehicle model.

3. Have an assistant start the engine, let it idle for a minute, and then turn it off.

4. As the engine turns off, use a pair of slip joint or vise grip pliers to squeeze and block the incoming and return lines. The rag should be between the pliers and fuel line to prevent damage to the hose.

5. Note the fuel pressure gauge reading for a few minutes.

  • If pressure remains steady, your fault if probably in the fuel pump anti-drain valve.
  • If pressure still drops, you have either a leaking fuel injector or bad FPR.

Check the video at the start of this section so that you have an idea how to do a maximum pressure test.

A bad fuel pump may cause low pressure.

A bad fuel pump may cause low pressure.

Whenever you have a fuel-system issue, fuel pressure should be one of your first diagnostic tasks.

As you can see, testing a fuel pressure regulator can be a simple process. With the help of a pressure gauge, a fairly inexpensive tool, you can find out if you need to replace the regulator or concentrate on other components or systems.

If you need to replace the regulator head over to How to Replace a Fuel Pressure Regulator, where you'll find the steps to install a new one. Most of the time, though, you'll learn that the root cause is a device in need of maintenance. And often, you can replace a failed or worn out component yourself and save some money over paying a repair shop.

Test Your Knowledge of FPRs

For each question, choose the best answer. The answer key is below.

  1. The FPR Builds Pressure Not the Fuel Pump
    • True
    • False

Answer Key

  1. True

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: For how long does fuel line pressure remain?

Answer: Fuel pressure decreases slightly after shutting off the engine. Then the pressure will hold for about five minutes then decrease slightly. But some pressure will remain steady usually after about 20 minutes.

Question: Is there any way you could check the vacuum on the regulator to see if the incoming and outgoing towards open, or how does that work?

Answer: You need to have the car at idle. You can unplug the vacuum hose and put your finger at the hose opening. If there's vacuum you'll feel a slight pull on the tip of your finger. If you need to know how much vacuum there is, you need to connect a vacuum gauge to it. Check the specification on your vehicle repair manual.

Question: My car has low fuel pressure that won't hold and the pressure increases with the removal of the regulator vacuum line. What could be the problem with my car's fuel pressure?

Answer: The pressure regulator might be working fine. The problem might come from a weak fuel pump or assembly, clogging fuel filter, leaking fuel injector perhaps.

Question: 2003 Chevy Tahoe 4.8l. It cranks but shuts off. Changed fuel filter. Now cranks but won’t start. Sprayed starter fluid and it runs but shuts off. Fuel pump or fuel pressure regulator?

Answer: Seems like a fuel system problem. You'll need a fuel pressure gauge to confirm low pressure. It'll help you to locate the issue. This could be a bad fuel pump or pressure regulator.

Question: What if the car just doesn’t start and I’ve never had it running? How can the fuel pressure system be tested?

Answer: Locate the fuel pump relay; you may be able to connect battery power to it. Have a fuel pressure gauge connected to the test port. Check the specification for initial pressure on your vehicle repair manual. The manual will help you locate the relay as well.

Question: I have replaced everything fuel related except the FPR in my 86' Ford F-150 302 cid. Now the truck won't start. It acts like it wants to though. Checked the Schrader valve and all I get is a little air. Could it be the FPR?

Answer: It's possible. The line can also be clogged. You may want to remove the fuel filter and open the ignition key and see if you get good fuel volume coming from the fuel tank. And test after the filter. It'll give you an idea if the problem is in the fuel pressure regulator before you replace it.

Question: The only way I can keep my Datsun 280z running is by clamping off the return line with small vise grips. This can't be right. Any answers?

Answer: The problem could be a worn out fuel pump or faulty pressure regulator. But check the fuel filter as well. If it's an old filter, it may be restricting fuel flow.

Question: I have a Nissan 180SX CA18DE engine. I have fuel coming out of the exhaust and the exhaust manifold. I've had the injectors cleaned and tested and still having this issue what can it be?

Answer: This usually happens with stuck-open fuel injectors. You can try removing one spark plug at a time and have someone crank the engine to see which cylinder is causing the issue. If the fuel injectors are working properly, you may want to check the fuel system, possibly a bad fuel pressure regulator or fuel return line.

Question: When turning off the engine, the fuel pressure is 43psi running spec on Tahoe 5.3L Flex Fuel. But after 10-15 minutes, pressure slowly drops to about 15 psi. Is this normal or bad? My injectors and FPR and fuel filter are new. Per article it seems like my fuel pump drain is allowing pressure backflow. Thoughts?

Answer: It seems like the fuel delivery system is draining fuel back into the tank. This could be a fault in the fuel pump or a valve, depending on your model. Your vehicle repair manual will give you the specs for your model and may help you diagnose the problem as well.

Question: I have a 2003 Acura CL type s, 6 speed. I recently had the injectors rebuilt, EGR valve and manifold cleaned out and a new fuel pump. My problem is, I get random hesitation usually from 1st gear to 2nd. It hesitates then kicks in hard. Also if I park the car then 0-15 minutes later I drive it, it will bog and hesitate then kick in and work fine. If I disconnect the vacuum hose from the FPR it doesn’t hesitate. I had it tested and the pressure is 55psi. What do you think is wrong?

Answer: Compare your readings to the specifications for your application. You can find the specs in your repair manual. Also, see how pressure behaves after a couple of minutes of engine running, when the hose is disconnected and after shutting off the engine. Go over the description in the post. Also, check the vacuum hose for damage and a tight connection. Also, this could be a sign of misfires at low speed or a problem in the ignition system.

Question: I have a 2003 Chrysler Town & Country. The van will start but usually takes about 4 or 5 turns of the key, about 5 seconds each turn. Once started, it will run fine with no problems. Once the engine is turned off, if it is cranked again immediately, it will start after one or two turns of the key. If it is allowed to sit for a while, it will take the 4 or 5 turns of the key again. Does this sound like a fuel pressure regulator problem?

Answer: It seems like the fuel system gradually loses pressure. This could be a leaking fuel pressure regulator, fuel injector or another component in the fuel system (pump, valve). If you have a fuel pressure gauge, measure pressure before you start the van, and after driving and compare measurements. This will tell you if system pressure has changed. You may need your vehicle repair manual to check specs.

© 2016 Dan Ferrell

Comments

Dan Ferrell (author) on August 31, 2020:

There could be an issue with the fuel pump. Also, check the fuel filter service interval. Make sure you change it as recommended.

Richard Stevens on August 30, 2020:

I have a 2004 Ford Explorer 4 liter according to the odometer on board diagnostics it's showing 128 pounds surges whenever I am at cruising speed just a little bit and my check engine light is on dude out at store part store is a fuel rail pressure sensor I've replaced it the light will go off as long as I keep running it but when I cut it off light comes back on

Dan Ferrell (author) on August 18, 2020:

You can have a failed or leaking pump, clogged fuel filter or failed pressure regulator. Sometimes you may be dealing with a leaking line but is not as common. Hope this helps.

Dewayne on August 16, 2020:

My 98 jeep grand cherocee is not getting fuel to in j.g ectors will pressure regulator cause this

Dan Ferrell (author) on May 27, 2020:

Make sure the coolant is still in good condition. Check belts for looseness; the water pump, if worn, can also be a problem. Make sure the radiator has no restrictions. There can be other potential problems. This other post may help:

https://axleaddict.com/auto-repair/What-Causes-a-C...

Raul Amores on May 24, 2020:

My vehicle is ford everest model 2009. I try to run my vehicle at maximum speed in order to test once in a while after running i felt the engine is very hot and when i start again the engine its hard to start my vehicle. Can you give some advise what im going to do?

Dan Ferrell (author) on December 28, 2019:

Check the idle air control motor (solenoid), sometimes either they go bad or get clogged. Another possibility is the ignition pickup coil in the distributor --ignition system. You may need the repair manual for your particular model to test the coil. Hope this helps

Mark Townsend on December 27, 2019:

I have a 302 windsor motor in my 87 ford f150. I start it, and the idling keeps going up and down. Ive replaced air filter, spark plugs,fuel filters,petrol pump. Any ideas???

Dan Ferrell (author) on December 27, 2019:

Check the fuel injectors - there could be an obstruction. If you have a code reader, check for trouble codes. There could be a problem with a sensor not sending a signal to the computer, usually a problem with the TPS (throttle position sensor).

Joe Elwell on December 27, 2019:

I have a 1985 2.8 camaro that will not start it has a new gas tank,new fuel sending unit, new fuel pump and a new fuel filter. I have 46 psi holding at the schrader valve it cranks over and will only run a few seconds with starting fluid.What do you think the problem could be that I should look for next?

Dan Ferrell (author) on December 24, 2019:

The pressure will drop slightly when engine speed increases. But too much drop may be a clogging fuel filter or worn fuel pump.

Oil leaks may be hard to trace. Try cleaning the area (wash the engine perhaps) and see if you can trace the oil as it begins to leak again. Look around the valve cover seal, specially. Hope this helps.

Victor on December 24, 2019:

So if there is low pressure when you rev the the vehicle, the pressure just drop what might be the problem

The other problem there is an oil leak that comes out of on the cam sensor on Audi a4 b8 2.0 tdi caga engine,i put the new cam seal but still the problem persist, where can the leak come from,or it might come out from the diesel pump or from the oil pump itself?

Dan Ferrell (author) on September 13, 2019:

The fuel injector(s) or fuel pressure regulator may be leaking. Test for fuel pressure before starting the car for the first time during the day. If pressure is low, you need to find the leak. Hope this helps.

fred on September 12, 2019:

after setting overnight very hard to start will start perfect rest of day

Dan Ferrell (author) on July 12, 2019:

Check to see if there's fuel in the rail and that the pump is running. If not, take a look at the fuel pump relay. Another possibility is a fuel pressure regulator.

Jimmy Holdman on July 12, 2019:

What if I put pressure test to rail and got 0 reading then replaced fuel pump and sensor assy in tank and I still get 0 pressure.its on a 1996 c1500 4.3L crew cad

Dan Ferrell (author) on June 04, 2019:

Consult the repair manual for your particular vehicle make and model. It has the correct specs for your car.

Hannes on June 04, 2019:

how to clean and ceck the injacktors of a geely 1.5 ck 1and the rail and pressure regulator of rail

Dan Ferrell (author) on March 25, 2019:

A stuck open EGR will probably allow the car to start, you'll notice a rough idle and possibly stall. You can try spraying some starting fluid through the throttle when starting the engine. If this seems like the engine wants to keep running with the fluid and then dies, the problem may be with the fuel system. Possibly lack of pressure.

Antwoine mac on March 23, 2019:

Changed fuel injector Check ingine light came on for egr valve..... Since then car stoped on me while i was driving i changed fuel pump thinking it was the cause yet car will not start it started up once in 4 days and died about 20 secs later.... Would egr valve cause this problem?

Dan Ferrell (author) on March 16, 2019:

You can check the fuel system pressure using a fuel pressure gauge. Most fuel injected models will have a pressure range between 30 to 45 psi. Check your reading against your manufacturer's specifications in your vehicle repair manual.

Will speedman on March 15, 2019:

I would like to know why it's so hard for some one to tell the fuel pressure psi on 1992 vw cabriolet it would really be nice if the simple question could be answerd i just hope every one is having a better day then i pease out

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