Fuel pressure regulator ford truck

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   How to test and replace :
Bad fuel pressure regulator on a 1994 Ford pick-up truck equipped with a 5.8 L Engine

In this page we will illustrate how to diagnose and replace a bad fuel pressure regulator on 1989-1999 Ford trucks.

The truck we are working on is a 1994 F-250 with a 5.8 L engine.

Take note that these steps also apply for other Ford trucks equipped with different size  engines , the fuel pressure is similar on all engines except 4.9 L. engines.

Normal fuel pressure for all engines except 4.9 L engine is as follows:

- Key on engine off: 35 to 45 psi
- Engine running:     30 to 45 psi
- Engine running with vaccum hose unplugged from fuel pressure regulator: pressure should increase 5 to 10 psi.

Normal fuel pressure for 4.9 L engines is as follows:
- Key on engine off :  50 to 60 psi
- Engine running :      45 to 60 psi
- Engine running, vaccum hose unplugged from fuel pressure regulator:  pressure should increase 5 to 10 psi.

- The symptoms this truck had due to a faulty fuel pressure regulator were: excessive black smoke, hesitation, hard to start, poor fuel economy, lack of power.
By the time the truck arrived at our shop, it could barely run, it seemed like it was running on 4 cylinders instead of 8, the engine was vibrating due to some of the cylinders not working, judging by the symptoms, we figured that the truck had a bad fuel pressure regulator, but to be 100% sure we performed some diagnosis.












Because of the excessive black smoke, we knew that the truck was running rich, we connected the scanner to read the oxygen sensor data, unfortunately, it showed "invalid", we decided to read the o2 sensor directlt from its electrical connector to find out if the O2 sensor was working. 

- We found out that the reason why the O2 sensor readings showed as "invalid" was because someone had left the wires laying on top of the exhaust pipe, that caused the plug to melt, we replaced the O2 sensor and proceeded to read its data, as we suspected, the readings were high showing a rich mixture, if you want to learn how to read the O2 sensor with a volt meter, visit our page oxygen sensor.







 To check the fuel pressure with a fuel pressure gauge, locate the test port located in the fuel rail, remove the plastic cap and set it aside. place a shop rag under the port and relieve the fuel pressure by gently pushing down on the small valve  in the center of the fuel port.







 - Next, connect the fuel pressure gauge to the test port as shown in the picture.

- Make sure that the gauge is not touching any moving parts, start the engine and read the fuel pressure, as you can see in this picture, the truck we are working on had 72 psi at idle, we unplugged the vaccum hose from the fuel pressure regulator and the pressure increased to 80 psi !. more than twice its normal operating condition.

- To replace the fuel pressure regulator, start by unplugging the vaccum hose attached to the top of the regulator.






 - Next, with an allen wrench, remove the two screws that secure the fuel pressure regulator to the fuel rail, even though you relieved the fuel pressure from the system, some gasoline will still spill, make sure that you have a shop rag under the fuel rail to catch the gasoline and avoid the truck from catching on fire!.

Pull gently upwards on the fuel pressure regulator, it should slide out fairly easy.


- Apply a thin coat of petroleum jelly to the seals on the new fuel pressure regulator, this will allow you to install the regulator on the fuel rail without damaging the seals.

Install the two screws that secure the fuel pressure regulator in place, connect the vaccum hose.

- Next, start the truck and read the fuel pressure, as you can see in this picture, the fuel pressure is slightly over 35 psi with the new fuel pressure regulator with the engine at idle, which is perfect for this truck.

Make sure that there are no fuel leaks around the fuel pressure regulator and coming out of the fuel test port.

We disconnected the fuel pressure gauge and allowed the truck to run for several minutes to clear the spark plugs that weren't working due to excessive fuel in the mixture, it gradually started running smoother as the plugs burned the gasoline.

NOTE: You may have to install new spark plugs in your truck if they are completely fauled.

We took the truck for a test drive, we noticed a pinging noise under acceleration due to over-advanced ignition timing, we adjusted the ignition timing to the correct specifications and we took it for a test drive again, the truck had plenty of power and smooth acceleration, almost like a brand new truck, if you want to learn how to set the ignition timing in a truck like this one visit our page Ford truck ignition timing.