Fuel pressure regulator

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  How the fuel pressure regulator works:

  The fuel pressure regulator is a device designed to maintain a constant fuel pressure for proper fuel atomization, we are going to focus on fuel pressure regulators designed for fuel injection systems knowing that there are very few carburated vehicles on the streets today since they are not produced anymore.

- How does a fuel pressure regulator work?
 The fuel pressure regulator is able to maintain proper fuel pressure to the vehicle it has been designed for because inside the regulator housing there is a spring pushing against a diaphragm, the spring pressure has been pre-set by the manufacturer for the desired fuel pressure, so the fuel pump has to pump enough fuel and enough pressure at the same time to overcome the spring pressure.
The extra fuel not needed is sent back to the fuel tank through the fuel return line.
When the vehicle is at idle, there is less pressure against the fuel coming inside the regulator  because the fuel pressure regulator has a vacuum hose attached to it, this way the fuel pressure will be lower ( from 5 to 10 psi depending on the system) due to the fact that the vacuum is forcing the diaphragm inside the regulator housing to have extra pressure against the spring, resulting in a lower fuel pressure when the car is at idle because  there is high vacuum inside the intake manifold;  when you accelerate and the vacuum drops, the fuel pressure increases to allow the engine to have more fuel as it needs it.

- Where is the fuel pressure regulator located?
  Every make and model has a different place for their fuel pressure regulators, for instance:
GM, Ford, Nissan, Toyota, BMW, and many more have the fuel pressure regulator mounted in the fuel rail, that way, the extra fuel exiting the fuel rail through the fuel pressure regulator will enter the fuel return line and it can travel back to the fuel tank.
Dodge  vehicles have the fuel pressure regulator inside the fuel tank mounted by the fuel pump, in some cases, even the fuel filter is part of the assbly, making it expensive to replace.
In conclusion:
Regardless of its location, the fuel pressure regulator has the same job, and that is to maintain constant fuel pressure to meet the engine needs.

- What are the symptoms of a bad fuel pressure regulator?
  The symptoms of a bad fuel pressure regulator include:
Lack of fuel pressure, excessive fuel pressure, black smoke and rich engine running condition, instant drop of fuel pressure once the vehicle has been turned off, delay building sufficient fuel pressure.

  - Click on image to learn how to diagnose and replace
a faulty fuel pressure regulator in 1990-1999 Ford Trucks

Related video:

We are going to show you how to replace a fuel pressure regulator in a 4.3 L. GM Vortec engine.
The vehicle we used to replace  the fuel pressure regulator is a 94 Chevy S-10 Blazer with a Vortec 4.3 TPI engine.

These were its symptoms:

The truck was running excessively rich, it was fouling the plugs extremely fast causing the engine to misfire and have tons of black smoke coming out of the exhaust pipe, what was so odd in this case was that the fuel pressure was normal!!  ( 58 psi ), the only engine trouble code we had was a code 45 ( O2 sensor indicates rich exhaust).
Well., we definitely knew that it was rich, specially because it was hard to breath if you stood next to it, plus your eyes would start watering real fast too.
- We scanned the truck to read its operating data, and we noticed that all the sensors were working properly, except for the Oxygen sensor being stuck on the rich side.
There was no other way for us to find out for sure, other than tearing this engine apart and look inside, we suspected a bad o-ring seal in the fuel pressure regulator could be the problem specially because even though the fuel pressure was normal, it would drop to zero almost instantly once the truck was shut-off.
If you want to find out if our suspicion was correct check our findings below as we remove the intake plenum to gain access to the fuel pressure regulator.













- Below are the steps required to replace a fuel pressure regulator on a 4.3 L. GM VORTEC CPI  ( Central port injected )Engine.

  - Step number 1:

 Loosen the two torx bolts that hold the plastic cover on top of the intake plenum and move it out of the way.

  - Step number 2:

  Loosen the hose clamps that secure the air intake hose to the throttle body and the air filter housing, and proceed to remove the air intake hose, make sure that you unplug the IAT sensor on the bottom of the hose as you remove it from the vehicle






  - Step number 3:

  Unplug all the electrical connectors from all the sensors attached to the intake plenum ( TPS, MAP, IAC etc ) and move the wiring harness out of the way







  - Step number 4:

  Unplug the throttle cable and the cruise control cable from the throttle body housing, next remove the three bolts that secure the bracket to the manifold and move it out of the way.

  - Step number 5:
  Remove the two nuts that secure the ignition coil to the intake plenum, next remove all other nuts that secure the wiring harness taking mental note of where they came from, next remove all the bolts and studs that hold the intake plenum attached to the lower intake manifold, unplug all the vacuum hoses and remove it from the vehicle.

  - Step number 6:
  Remove the two tamper proof torx screws that hold the fuel pressure regulator in place, remove the oval shaped bracket, and proceed to remove the fuel pressure regulator.

NOTE: If you look close at this picture, you can see the different color of the intake manifold under the fuel pressure regulator, this was caused by fuel leaking out of the fuel pressure regulator. So.... we were right, our fuel pressure regulator was the problem in this vehicle.

  - Step number 7:
  Lubricate the fuel pressure regulator's o-ring seals with petroleum jelly. This is the best lubricant to use due to the fact that it dissolves very easy in gasoline without a possibility to clog the fuel injectors. Once the seals are lubricated, proceed to install the regulator.

Please note that even though this fuel pressure regulator doesn't have a vacuum hose attached to it, it has a small orifice that provides the right amount of vacuum for its operation, when installing the regulator, make sure that the orifice is on top.

  - Step number 8:
  Clean the mating surfaces in both parts; the lower intake manifold and the intake plenum, they should be free of old gasket material and any other contaminants.





  - Final step:

  Install a new gasket and proceed to install the parts you removed from the vehicle in the reverse order you took them off, if you do this correctly, you shouldn't have any parts left at all and everything should be in its place.



 As we mentioned earlier, the fuel pressure regulator in this vehicle was the cause of black smoke, fouled spark plugs, rough idle and misfiring, poor fuel economy and a engine code 45.

Since we needed to install new spark plugs to ensure that the truck would run well, we decided to install new spark plug wires and distributor cap and rotor as well, we fired it up and it runs as good as new.

We hope that this information we just provided for you helps you to understand how fuel pressure regulators work and in the event you decide to replace a fuel pressure regulator in your vehicle, you will have a step by step guide on how to do it.