Fuel injection question

[mikkelstuff]

While replacing the stock fuel filter in my 2002 3.0L 4WD Ranger XLT, I added an inline fuel pressure gauge.

Now checking this gauge I see that fuel supply runs at about 70 psi with the engine running as expected but the pressure immediately goes to zero when turning the engine off. Obviously there is no accumulator (or working accumulator) in the fuel supply system. Is this correct for the system?

Also, I would have expected the fuel pressure to rise when turning the ignition switch to just the "on" position but that is not happening either.

If fuel pressure is zero with the engine off, how does it start up immediately when turning the ignition switch?

This is quite different than my old '82 fuel injected VW Rabbit.

 

[Dirtman]

Where did you install the guage? Off of what line? It should hold 65psi for weeks... Something is leaking, you installed the guage wrong, or the return valve on the fuel pump is dead. Can you hear the pump run for 2 seconds when you turn the key to the ON position? If so I'm leaning towards the guage is somehow installed wrong or leaking.

Check it with a real guage on the fuel rail port.

 

[RonD]

+1 ^^^

2002 Ranger has whats called a Returnless fuel system, used from 1998 to 2011 in Rangers

It just has 1 fuel line at the engine, so no "return line" like 1997 and earlier Ranger had, but it DOES have a Return line on the fuel filter, 3 port fuel filter

On the fuel pump assembly in the gas tank is the fuel pump AND a Fuel Pressure Regulator(FPR)

Fuel pump>>>>>>>>>>Filter>>>>>>>>>>>>>>>>engine

3rd port on Filter>>>>>>>>>FPR>>>bottom of gas tank

The fuel pump can provide up to 90+ PSI
The FPR in the gas tank starts releasing fuel back into the tank after about 55-60psi

70psi is too high but could just be the pressure gauge calibration, or a problem with FPR

When new the system will hold pressure with Key Off above 40psi, but anything above 20psi is usually OK
When you turn on the key the computer will run the fuel pump for 2 seconds ONLY, its a safety thing
That 2 seconds adds 10 psi to the existing pressure
You can cycle key OFF and ON and should get 10psi more with each ON and another 2 second run time

After engine starts(above 400rpms), computer turns on fuel pump full time(cranking speed is 200rpms)

Drop to 0psi usually means the check valve inside the fuel pump is bad, or the FPR is leaking, both are inside the gas tank so there would be no external smell of gasoline
If you SMELL gasoline then its from an external leak, lol

In your description, as Dirtman said, its more likely an issue with the newly install pressure gauge system
Because no, your engine would not start with 0psi fuel pressure, so its not actually 0psi

 

[mikkelstuff]

This is the spin-on filter installation without the filter. This Wix/NAPA filter mount has four ports - two inflow and two outflow. I used the two filtered outflow ports for the engine fuel supply and for the tank return. I only need the one inflow port for the pump fuel supply. The fuel pressure gauge is attached to the second inflow port and should read fuel pressure in the filter mount. There are no restrictions between inflow ports or outflow ports.

I cannot attest to the quality of the $14.00 fuel gauge.

 

[mikkelstuff]

Reading further in the 3.0L section I see that a leaking injector can do this pressure bleed. I will try the leaking injector test. I have already had to replace one bad injector which repeatedly gave a cylinder misfire code.

 

[Dirtman]

I'm 87% sure you have that plumbed wrong and the fuel isn't actually flowing through the filter element...

Edit - nevermind as long as the lower left hose is the feed line and not the return it's good.

 

[mikkelstuff]

Yes, lower left line is the pump feed line.

I tried the leaking injector test and the injectors passed the test.

So now I either have a sorry gauge or, as I understand it, a problem with either the fuel pump check valve or fuel pressure regulator. Still, the engine starts with really no issue.

I do believe, as recommended, that I need to check this out with a high quality fuel pressure gauge connected to the fuel rail port.

Anyone have a picture or diagram to show me this fuel rail port? and can I leave a gauge attached to this port?

 

[Dirtman]

The Guage port on the fuel rail is a Schrader valve, same as a tire stem and will have a tire valve cap on it.

I don't think it's actually leaking down because it would take longer to start, I still think it's something with that Guage.

 

[mikkelstuff]

Found the fuel rail port. My sorry repair manuals don't even cover this. So ordered a decent replacement fuel gauge for the spin-on fuel filter mount and a fuel pressure tester to connect to the Schrader valve.

Many thanks to Dirtman, RonD, and all the Ranger Station members. I simply could not fix these Ranger problems without your help.

 

[mikkelstuff]

Got a replacement $44 Aeromotive fuel pressure gauge from Amazon to replace the cheapy under the truck. However, the Aeromotive instructions say that the gauge must be mounted with the face in a vertical orientation. Interesting! I never knew pressure gauges to have that limitation. Perhaps that is why my cheap gauge is reading zero pressure with the engine off.

I then asked JEGS and Summit about this and they both say all their gauges work in any orientation - including the Aeromotive! So much for asking.

Then I noted that a quality fuel pressure gauge from McMaster-Carr, guaranteed to work in any orientation, costs over a $100!

 

[mikkelstuff]

Got a good fuel injection pressure test run on the Ranger. The pressure runs right at 65 psi with the engine running. Once the engine is turned off, the fuel pressure immediately drops to about 20 psi and then slowly sinks to 0 psi.

I assume this means the FPR or fuel pump check valve are bad. I notice lately that the truck starts much better if I cycle the key switch a couple of times before attempting to start the engine.

So does this imply immanent failure of either the FPR or fuel pump? Or can I just keep cycling the key switch?

What about adding a check valve to the steel fuel supply line to the fuel rail? That should maintain 65 psi in the fuel rail unless that is hazardous.

 

[Roert42]

Sounds like you have an issue with the check valve on the fuel pump. If it was the FPR I would think you would have a hard time holding 65psi.

You could keep cycling the key to prime the system, I don’t think it would cause any issue. Just more work.

I know some inexpensive liquid filled gauges have a breather hole on the top. If you mount them sideways then all the liquid pours out. Normally that would have a plug in for shipping so you could just keep the plug in.

 

[Dirtman]

I wouldn't immediately blame the pump. I've yet to see a fuel injector test gauge that doesn't leak...

 

[Roert42]

I wouldn't immediately blame the pump. I've yet to see a fuel injector test gauge that doesn't leak...

I agree with you. However, he did state that he has been having issues with cold starts taking a while, and if he prime the enshrine a couple of times it helps.

that’s the main thing that leads me to believe there is a bad check valve.

 

[RonD]

For 1998 and up Rangers its a moot point because the fuel pump assembly has both the pump, and FPR, so both are new when you change it