P38A Fuel line check valve?

wammers said:

The fuel pressure regulator ETC8494. Unless the lift pump has a leak back problem or is not being switched on start up.

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Everything tells me it’s a leak back problem. I get full pressure with the key on but engine off.Then when the key is off the pressure goes with it. Also since the fuel pressure regulator only regulates while under vacuum; is that correct? Or does it also act like a check valve with no vacuum applied?

My plan for now is to fit a one way valve and report back. They’re cheap enough to give it a shot.

P38Rover said:

Everything tells me it’s a leak back problem. I get full pressure with the key on but engine off.Then when the key is off the pressure goes with it. Also since the fuel pressure regulator only regulates while under vacuum; is that correct? Or does it also act like a check valve with no vacuum applied?

My plan for now is to fit a one way valve and report back. They’re cheap enough to give it a shot.

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Ok carry on you know best. Think it maybe an expensive experiment.

wammers said:

Ok carry on you know best. Think it maybe an expensive experiment.

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I mean if I can determine it is the FPR that is faulty then I would gladly change that out. Nothing I hate more than just throwing money at a problem and hoping it works. But as far as I can tell it’s working to maintain pressure (36 PSI) when I rev the engine and at idle. While normal driving, towing, downshifting up a hill.. everything 100%. No engine codes.. ONLY when the key is turned off does the fuel pressure leak down....? I dont know what else to try. Symptoms point to leak down problem. Or am I misreading it? Any other tests that you can recommend? The relay is also pretty new but I suppose I can test that too..Which probably isnt an issue because my symptoms only happen with the key off. Also my injectors are fairly newly rebuilt, so im hoping they are not all leaking at once. But yeah anything is possible I guess..

Watch this and read RAVE. Not a great video but does show the effect of vacuum or pressure in the manifold.

Fuel pressure regulator - (up to 99MY only)
The fuel pressure regulator is a mechanical device controlled by manifold depression and is mounted at the rear of the engine in the fuel rail. The regulator ensures that fuel pressure is maintained at a constant pressure difference to that in the inlet manifold. As manifold depression increases, the regulated fuel pressure is reduced in direct proportion. When pressure exceeds the regulator setting, excess fuel is spill returned to the fuel tank swirl pot which contains the fuel pick up strainer.

As far as I can tell the system is pressurised when you turn ignition on and pump relay energises. Unless there's a check valve already fitted in the LR design, then it will drop back when off.

pwood999 said:

Watch this and read RAVE. Not a great video but does show the effect of vacuum or pressure in the manifold.

Fuel pressure regulator - (up to 99MY only)
The fuel pressure regulator is a mechanical device controlled by manifold depression and is mounted at the rear of the engine in the fuel rail. The regulator ensures that fuel pressure is maintained at a constant pressure difference to that in the inlet manifold. As manifold depression increases, the regulated fuel pressure is reduced in direct proportion. When pressure exceeds the regulator setting, excess fuel is spill returned to the fuel tank swirl pot which contains the fuel pick up strainer.

As far as I can tell the system is pressurised when you turn ignition on and pump relay energises. Unless there's a check valve already fitted in the LR design, then it will drop back when off.

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Thanks for the reply. Its like the guy says in the first couple seconds of the video. He says its been a couple hours and went to the store to get spark plugs and he still has fuel pressure. Mine goes to zero in about 3 seconds when I take the key out.

In the morning tomorrow I will do some more hands on testing. Also take another good look at the rave. Have a good day everyone.

I appreciate all your suggestions.

NAS vehicle has lots of extra stuff. Definitely check rave.

Can anyone confirm if the fuel pressure regulator's purpose is also to be a one way valve when the engine is NOT supplying vacuum?

I cant find anything in the RAVE that suggests that there is a replaceable one way valve anywhere in the fuel system or that the FPR does that with no vacuum applied.

Maybe Im just being a Yankee Doodle Dandy and I was searching for driveshaft when I should be looking for propshaft, hood instead of bonnet, valve cover instead of rocker cover etc..etc.. Am I getting the wording wrong? Check valve, one way valve, non return valve... What am I missing?

The FPR is just that. It is designed to maintain the pressure in the system at a fixed point above manifold vacuum. At idle there is a high manifold vacuum (low pressure) as you open the throttle the manifold vacuum is destroyed and the absolute pressure rises, so the fuel pressure regulator supplies fuel at a higher pressure to the injectors.

Any fuel over the pressure it is currently operating at is spill returned to the tank.

The fuel pump should have a one way valve in it to stop fuel drain back as well as a HP relief valve.

Have you removed the fuel pump and had a look at it? Is there a bit of dirt in the valve? Is it time to replace a worn part?

Marshall8hp said:

The FPR is just that. It is designed to maintain the pressure in the system at a fixed point above manifold vacuum. At idle there is a high manifold vacuum (low pressure) as you open the throttle the manifold vacuum is destroyed and the absolute pressure rises, so the fuel pressure regulator supplies fuel at a higher pressure to the injectors.

Any fuel over the pressure it is currently operating at is spill returned to the tank.

The fuel pump should have a one way valve in it to stop fuel drain back as well as a HP relief valve.

Have you removed the fuel pump and had a look at it? Is there a bit of dirt in the valve? Is it time to replace a worn part?

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Yup that’s how I understand it. The FPR requires vacuum to do what it’s designed to do. It’s just that a well known member suggested that my issue was the FPR, but mine doesn’t show any signs of failure and it’s working exactly as I understand it should. So I’ve been searching endlessly for the last couple days for information or tests to try on that issue.

All my symptoms currently point to a one way valve that has failed. A couple years ago I’ve changed out my fuel pump. I did it the proper way by dropping the fuel tank and I’m really not trying to go in there again if I don’t have to. Very possible that something is jammed in the valve. I do a lot of off-roading so the fuel in my tank is always violently sloshing around. Definitely enough to kick up some debris into the filter/valve.

Do you have a source for the information about the high pressure relief valve or the one way valve in the pump? I can’t find any information on that either.

Much thanks for the reply

So unless someone can confirm that the FPR( which is a $100 part) is at fault for not keeping the fuel line full after the engine has been shutdown..

Iam going to have to follow my logic and install a one way valve. Which is a $5 gamble vs a $100 one.. And if that doesn’t work then I guess I’ll have to throw another hundred dollars at her and hope it works. Even though all testing shows that the FPR is fully functional...

I’m nearing the stage where I will soon sacrifice a virgin carburetor to the fuel injection gods..Don’t know what else to do or try or test. I appreciate any and all suggestions.

One thing for sure is that I cannot use my Rover for what it is intended for in this condition. There’s no way I’m driving more than 10miles away from my house let alone the normal 20-30 miles into the woods that I usually travel.

P38 - which engine do you have?

romanrob said:

P38 - which engine do you have?

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GEMS 4.6

Whichever part it may be,

Why would you want fuel pressure when the engine is off anyway, I don’t see the issue?

RangeRoller dt said:

Whichever part it may be,

Why would you want fuel pressure when the engine is off anyway, I don’t see the issue?

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So I can start the vehicle immediately after I shut it off. Or even immediately after a long time sitting.. If I only used it for driving around town I wouldn't care and I would let whatever part it is to completely fail or leave me stranded.

But I use my rover for at least 80% off-road use. Often I am 20-30 miles deep into the woods and away from any paved road or cell signal. Sometimes theres another 30 miles from the "maintained" road to a town.

I dont particularly enjoy the sinking feeling when I go to start my engine and it doesn't fire the first try when Im so far from home. Not very confidence inspiring. I need it fixed.

Ah it dont like starting warm?

Thought you said you get fuel pressure as soon as you turn ignition on.

RangeRoller dt said:

Ah it dont like starting warm?

Thought you said you get fuel pressure as soon as you turn ignition on.

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Its both. And completely randomly. I believe when I get a no start condition it is because there is air in the line. And the air needs to cycle out before I can get it running normal. My theory is that when I get the stumbling to start condition it is because little smaller pockets of air. Just a theory.. I really hope that a check valve can fix me up.

I have one arriving tomorrow we will soon find out.

If you have fuel pressure with ignition on and when you switch off it disappears there is only one place to look and that is the fuel pump.

According to this thread on RR.net there should already be a check valve in the pump . . . . . except some aftermarket pumps don't have them !!

How long does it actually take to prime ? Be patient or drop the tank & sort the pump. !