What is the fuel pressure supposed to be?

I get 30 when at idle and 28 when i get on the throttle. The check valve apparently is bad because it leaks to 0 very quickly after the truck is shut off.

Where is the check valve on the positive flow line? I assume in the tank with the pump?

If i pull the vacuum off of the pressure regulator it will jump pressure to 40.

Just looking for some incite.

Oh and the truck starts hard due to know initial fuel pressure.

 

Approx 30 psi at idle is correct,and 40 psi with no vacuum present is also correct.
Pressure will bleed down when you shut off the key-that's normal.
JL

 

My dads, super crew doesnt. Thats what we used for comparison. It held pressure.

 

If you're "Just looking for some incite" maybe I can help.

Overnite, or any other long period sitting, even a good "check valve apparently" allows fuel pressure to drop to 0 & that should not in itself cause hard starting. A good fuel pump should almost instantly provide correct fuel pressure. In many instances its normal for "initial fuel pressure" to begin at 0.

Does it always suffer hard starts, whether hot or cold? The rest pressure test I see is only for a 5 minute wait, not enough time for a hot motor to cool. "I assume" it takes more than a single "check valve" to maintain rest pressure. My guess is 1 is part of the fuel pump & the other is part of the fuel pressure regulator. There is a supply & a return line, both are actually "positive flow" lines. The fuel regulator essentially establishes pressure by restricting this "positive flow".

 

It returns to 0 with in 2 seconds of being turned off.

Also the pump will turn on for a few seconds when the key is turned to the on position but stops once pressure i reached, then the pressure will bleed back down.

It seems to be hit or miss right now. Weather dosnt seem to be the problem. I have tried several different gas stations thinking that bad fuel was possible.


I was just using positive as the term for the line coming to the engine. Im aware of the two separate lines. And since the regulator seems to still be regulating fuel pressure, due to the fact that pressure changes when vacuum is removed from the regulator. Pump is apparently meeting pressure needs. It must be the check valve.

I would like to know where its located at.

 

Also i know that its not supposed to return to zero since my fathers screw will remain at 30 for some time after being turned off. So since myne goes to 0 within a couple seconds shows that there is something wrong with the system.

 

If there's a check valve(and I really don't think there is a dedicated check valve),it's going to be in the fuel pump assembly.
JL

 

There is no mention of a check valve in the fuel system. The vehicle:

is equipped with a multiport fuel injection (MFI) system.

has separately controlled fuel injectors mounted to the intake manifold for each cylinder.

fuel injectors are supplied with pressurized fuel from the fuel pump through the fuel injection supply manifold.

fuel injection supply manifold is equipped with a fuel pressure regulator.

fuel pressure regulator controls the pressure going to the fuel injectors.

has excess fuel to the fuel injectors returned to the fuel tank.

If there is one it would have to be in the fuel pump assembly. Fuel pressure KOEO is to be 35-45 psi. With the engine running, 28-50 psi. There is no specification for when the key is off. Good luck!

 

Sorry to be somewhat ambiguous by posting: "I assume" it takes more than a single "check valve" to maintain rest pressure. My guess is 1 is part of the fuel pump & the other is part of the fuel pressure regulator. However I've often been slammed, accused of being a know it all. Plainly it takes more than a single "check valve" to maintain rest pressure for at least 5 minutes.

The pump circuit is designed to run only briefly w/key on "but stops" under PCM control, unless there's signals from motor turning over-not b/c "pressure i reached". The only "weather" I was interested in was under the hood, if hard starts are w/hot &/or cold motor?

If "It returns to 0 with in 2 seconds of being turned off" it clearly fails the 5 minute rest pressure test.

Reading the "fuel pressure regulator controls the pressure going to the fuel injectors" & "There is no mention of a check valve...If there is one" seem a bit backward to me. There has to be 2 functioning valves to maintain rest pressure in the fuel rail. I'd thought the regulator is actually located downstream, past the injectors.

Since the fuel reg is critical to fuel pressure while running & at rest, is relatively inexpensive & is quite easily replaced-it would be my #1 suspect. These regulators can also fail by leaking internally, check vacuum line for signs of raw gas. If injectors are leaking down you may notice black smoke/sooty exhaust pipe. If "there is something wrong" w/the fuel pump I presume you know its relatively expensive & difficult to replace.

I'd go by the process of elimination. If a fuel reg doesn't restore rest pressure to the 5 minute spec, resolving your problem & you're not blowing puffs of black smoke at start up, the fuel pump might be leaking down.

Sorry, but IMO it doesn't have to "be the check valve" & that is not a replacement part. FORD & most others, use the terms supply & return lines. Adding "positive flow line" isn't particularly useful.

 

Isnt the regulator on the return line thought? Im pretty sure it is.

 

Also the only reason i stated check valve, is because the previous style ford used them. I had a similar issue on my 92 bronco. Replaced the check valve and solved the problem.

I understand the trucks are different.

Anyways.

 

IMO the return line emanates from the fuel reg. What part of a check valve being an integral component inside these fuel pumps don't you understand? To bad resolving "a similar issue" quite often doesn't apply to another specific problem.

 

so that would be the other "check valve" or what ever that would allow the fuel pressure in the rails to stay up after the pump is off. The pump probably is the stop on the supply line as well. I probably need to replace the pump and other internals in my tank.

Been having some troubles with fuel level sensor as well.

 

The advent of ethanol has had serious implications for fuel quality & fuel system reliability. The alcohol mixes easily w/water resulting in a number of undesirable effects, including corrosion, bacterial growth & degradation of synthetic plastics. Fuel level sensors, fuel reg diaphragms, fuel filters, etc. have all become less durable. It wouldn't take much goop to prevent a check valve from closing properly.

Ripoff gas retailers have even been caught adding water. I'd be particularly concerned if Brand X gas was used habitually. Being in IA your F150 has probably had more alcohol thru it than most.

Obviously if you plan to drop the tank to fix the level sensor it could be a good idea to replace an original pump on a 10 YO pickup you want to keep. Especially if what you see inside looks gunked up. I'd still try a cheap/easy fuel reg 1st, even a used U-Pull part, just to see if it makes a difference.

 

What do you think "rest pressure" also referred to as "Fuel system hold pressure" means?

This test is done "when the key is off" after running, the general spec is that the systems still hold 30 to 40 PSI after 5 minutes. Some other FI systems specify holding pressure 30 minutes or more.