Questions on fuel pressure. Need ideas

[Redrider2911]

Originally Posted by CowboyEdition

Is there an easy way to plumb your gauge into the system between the lift pump and injection pump inlet?

I'm 99% that's where he said he already has it plumbed in. I don't know where else he would put it...

[Ethan12v]

Just for some clarification on my setup here's a picture, its at a weird angle (you can see the barrels on the right, shutoff solenoid bracket on the left) but its on the pump inlet, Tork Tek snubber, then it goes to a t block, at the end there's a plug, on top is the boss fitting for the braided steel line that goes directly to my fp gauge sending unit.

[CowboyEdition]

Originally Posted by Redrider2911

I'm 99% that's where he said he already has it plumbed in. I don't know where else he would put it...

My understanding is that it's on the inlet banjo - meaning it's measuring pressure inside the injection pump. I'm curious what the line pressure is before the banjo. If its higher than inside the injection pump, the banjo is a restriction. A pressure gauge can be T'd in anywhere, it just isn't necessarily convenient.

Sent from my SM-G870W using Tapatalk

[Redrider2911]

While in theory it's possible for their to be a restriction there... he has it plumbed in exactly how 100s of other people have...

[Redrider2911]

Also, if the problem was before the injection pump then he wouldn't see a significant rise in pressure by kinking the return line.

If he can get the line pressure over 50psi by kinking the return Line, then the problem is the OFV. If he can't, then I would suspect the lift pump (maybe a bad check valve in the lift pump) or the cam lobe the lift pump rides on.

[Ethan12v]

Originally Posted by CowboyEdition

My understanding is that it's on the inlet banjo - meaning it's measuring pressure inside the injection pump. I'm curious what the line pressure is before the banjo. If its higher than inside the injection pump, the banjo is a restriction. A pressure gauge can be T'd in anywhere, it just isn't necessarily convenient.

Sent from my SM-G870W using Tapatalk

That's a tough one because its that steel line and it has the banjo up by the IP and a flare type fitting down by the LP, ill have to rig something up like a 3/8 fuel line that has both those type fittings on it and splice a gauge in the middle of it all

Originally Posted by Redrider2911

While in theory it's possible for their to be a restriction there... he has it plumbed in exactly how 100s of other people have...

This comes into my mind as well. If that was the cause of the problem then there would be so many other people that would have the same issue, with the exact same thing.

[CowboyEdition]

Originally Posted by Redrider2911

While in theory it's possible for their to be a restriction there... he has it plumbed in exactly how 100s of other people have...

I'm not suggesting incorrect gauge installation - I'm suggesting a possible faulty part. If the fuel passages in the Snubber Banjo were drilled too small by some fluke, or a couple were missed all together there could be a pretty good restriction. I'm not saying it has to be the inlet. The guys looking for ideas and he's checked all the easy stuff already. I also mentioned a weak spring or bad check-valve in the lift pump - all of which create a flow problem.

Originally Posted by Redrider2911

Also, if the problem was before the injection pump then he wouldn't see a significant rise in pressure by kinking the return line.

If he can get the line pressure over 50psi by kinking the return Line, then the problem is the OFV. If he can't, then I would suspect the lift pump (maybe a bad check valve in the lift pump) or the cam lobe the lift pump rides on.

When flow is restricted, pressure on the supply side goes up. You have 21psi at idle while flowing some fuel through the OFV back to return. Kink off the return line, now you have no flow (or minimal flow, as the injection pump is using a tiny bit) - pressure goes up even if there is a restriction somewhere on the supply side. Because there is no flow, the pressure rises on both sides of the restriction. So yes, there can be a restriction on the pump inlet and still produce 50+psi when the return line is kinked.

Seeing 50+psi with a kinked return line proves the lift pump can make pressure - it does not prove it can produce flow under pressure. Therefore it does not prove the OFV is a problem.

Read back to where he gutted the OFV, reinstalled it and pinched off the return until he had 21psi. Then he reved it up to 1500rpm and fuel pressure dropped off - same problem as when the OFV was regulating the pressure. THAT is a flow problem. Fuel pressure should have increased as fuel flow increased with rpm, as the restriction (half-pinched return hose) would have become greater with the increase in fuel flow.

Sent from my SM-G870W using Tapatalk

[CowboyEdition]

Originally Posted by Ethan12v

I have installed a new lift pump.... From orieleys... I know (the brand is Precision).

Was it doing this before you installed the new lift pump?

Sent from my SM-G870W using Tapatalk

[Redrider2911]

I guess there could've been a pluke and that part was drilled with only super small pilot bit...

If the gauge is only reading 21 psi due to a flow restriction on the inlet and the OFV is cranked all the way down or even kinked off, then couldn't we stand to reason that there is no volume even being returned through the return line? (A test I suggested but haven't heard back on). The OFV valve does not maintain pressure by restricting flow through a small orifice... it maintains pressure by bleeding off EXCESS flow ABOVE the pressure the spring is set at. So either there is no excess flow/sufficient flow period; or the OFV is bleeding off too much flow. Once we know the answer to that we can narrow it down to faulty OFV or faulty lift pump. MAYBE a bad banjo bolt...

If you reread what he said about kinking the line, he suggested that he was only kinking it partially in order to maintain about 21psi. That's why I asked him specifically what the pressure reads if he kinks it completely. That test and a visual inspection of the return line flow volume should tell us quite a bit.

[Ethan12v]

Originally Posted by Redrider2911

I guess there could've been a pluke and that part was drilled with only super small pilot bit...

If the gauge is only reading 21 psi due to a flow restriction on the inlet and the OFV is cranked all the way down or even kinked off, then couldn't we stand to reason that there is no volume even being returned through the return line? (A test I suggested but haven't heard back on). The OFV valve does not maintain pressure by restricting flow through a small orifice... it maintains pressure by bleeding off EXCESS flow ABOVE the pressure the spring is set at. So either there is no excess flow/sufficient flow period; or the OFV is bleeding off too much flow. Once we know the answer to that we can narrow it down to faulty OFV or faulty lift pump. MAYBE a bad banjo bolt...

If you reread what he said about kinking the line, he suggested that he was only kinking it partially in order to maintain about 21psi. That's why I asked him specifically what the pressure reads if he kinks it completely. That test and a visual inspection of the return line flow volume should tell us quite a bit.

Ill do the complete line pinch tonight if its safe to do so for the IP, but this would not be a problem with the injection pump or injectors correct?

[CowboyEdition]

Originally Posted by Redrider2911

If the gauge is only reading 21 psi due to a flow restriction on the inlet and the OFV is cranked all the way down or even kinked off, then couldn't we stand to reason that there is no volume even being returned through the return line? (A test I suggested but haven't heard back on). The OFV valve does not maintain pressure by restricting flow through a small orifice... it maintains pressure by bleeding off EXCESS flow ABOVE the pressure the spring is set at. So either there is no excess flow/sufficient flow period...

Yep, that's pretty much what I've been saying all along. There may be very little volume being returned. ie flow problem, not OFV problem.

Originally Posted by Redrider2911

If you reread what he said about kinking the line, he suggested that he was only kinking it partially in order to maintain about 21psi.

Yes, he did say that, when he gutted the OFV. Read back a little further and you'll find he also said:

Originally Posted by Ethan12v

HOWEVER, when I kink my return line, pressure will shoot up like everything is hunky dory.

and:

Originally Posted by Ethan12v

If I completely block it off it will spike to 60psi.

Originally Posted by Redrider2911

That's why I asked him specifically what the pressure reads if he kinks it completely. That test and a visual inspection of the return line flow volume should tell us quite a bit.

He's already listed the pressure results of this test. 60psi with return kinked. A visual would still be good, but his two return pressure tests have already told the story - there is a flow problem.

In my mind, the next step is check the injection pump inlet for restriction, since the supply side of the lift pump has already been gone through fairly well. If that's good, then it's time to take one last look at the supply side of the lift pump. Or just change it and hope that was the problem.

[CowboyEdition]

Originally Posted by Ethan12v

Ill do the complete line pinch tonight if its safe to do so for the IP, but this would not be a problem with the injection pump or injectors correct?

Not a problem for either injectors or injection pump for the purpose of testing.

Was it doing this before you changed lift pumps?

[Redrider2911]

Somehow I missed the part where he said it would shoot up to 60psi. Ok, so we agree on the part I was trying to explain about how the OFV works; the following is my point.

If there is a flow inlet restriction that is only allowing the injection pump to only see 21psi even with the OFV cranked down to max pressure setting (assuming somewhere around 100psi?), then kinking the line would have absolutely no effect on the pressure since the OFV would already remain closed until the set PSI was reached. The fact that kinking the return line raises pressure, tells me that excess flow is leaking by the OFV when it is not supposed to.

[CowboyEdition]

Originally Posted by Redrider2911

Somehow I missed the part where he said it would shoot up to 60psi. Ok, so we agree on the part I was trying to explain about how the OFV works; the following is my point.

If there is a flow inlet restriction that is only allowing the injection pump to only see 21psi even with the OFV cranked down to max pressure setting (assuming somewhere around 100psi?), then kinking the line would have absolutely no effect on the pressure since the OFV would already remain closed until the set PSI was reached. The fact that kinking the return line raises pressure, tells me that excess flow is leaking by the OFV when it is not supposed to.

I'm thinking there is some flow past the OFV and by 1500rpm that flow is used up by the injection pump. OFV closes off and fuel pressure drops as the injection pump is using all the fuel that's being supplied.

If the OFV was the problem, then as I said earlier, when he regulated pressure to 21psi by pinching the return line down (with OFV gutted, therefor eliminated ), fuel pressure would have continued to increase as rpm increased because flow increases with rpm on a piston pump and that increased flow would try to push through the same size restriction, thus raising pressure. But fuel pressure didn't continue to rise. It dropped off just as it did when the OFV was regulating pressure, indicating a flow problem fedora the OFV.

Also, as you said earlier, the OFV balances spring pressure against flow to regulate fuel pressure. Set to 21psi at idle, pressure increases with rpm to say 35psi because flow increases against the ball and spring. When flow increases, the ball is pushed harder against the spring and further away from the seat which increases spring tension preventing the ball to move further. So in this situation if the OFV were the problem, then as flow increases the spring tension would somehow have to decrease, allowing the ball to move further away from the seat which would cause pressure to drop. I don't see that happening.

Sent from my SM-G870W using Tapatalk

[Ethan12v]

Originally Posted by CowboyEdition;2606360[B

]I'm thinking there is some flow past the OFV and by 1500rpm that flow is used up by the injection pump. OFV closes off and fuel pressure drops as the injection pump is using all the fuel that's being supplied[/B].

Sent from my SM-G870W using Tapatalk

That's where I'm at with it as well. I had to work super late last night so couldn't even touch the truck but my lift pump before this new one could barely build up to 30psi when the return line was kinked so it was bad without a doubt. But this is why I'm praying its not an issue with the injection pump. I'm going to do that prefilter bypass tonight and see where that puts me

[Ethan12v]

Did not want to double post but I mic'd my spring and im thinking i need to somehow get ahold of Tork Tek and see what exactly the specification is for it. Here's my measurement as it sits now. Using my high dollar kobalt micrometer of course..

[Redrider2911]

Put a longer or stiffer spring in there or a second spring like a bic pen spring. Then tighten her down and see what you can get. I'm still convinced that your problem is something wrong with the overflow. While your in here messing with your fuel system it also wouldn't hurt to change the spring in the lift pump to a comp cams spring.

[badbowtie]

I am wondering about the guts of the aftermarket fuel pump. I wonder if it has the small plunger and just can't keep up with the increased demand.

96 3500 5x018 7mm dvs 64.5sxe
90 d350 5x010 hx35

[Destroked 450]

I have a similar issue but have narrowed it down to the lift pump.
We did a complete engine rebuild and fuel system upgrade last fall.
AN 10 fittings with 5/8 braided line from inside the tank to the lift pump, Raycor prescreen with 1/2" NPT fittings replaced the stock prefilter, no reason not to have plenty of fuel to the lift pump.
The Carter lift pump (installed in 07) still looked good and appeared to pump fuel at a decent rate so I reused it.
After getting the engine running I adjusted the overflow valve to 28 psi at idle, this gave me 32 psi at 1500 and dropping back to 25 at 2600 (Highest I want to rev a new engine). After 2000 miles it still idles at 28 psi and climbs to 30 but then drops back to 18-20 psi under heavy throttle.
The spring in the lift pump isn't able to keep up with the additional fuel demand, I have a replacement pump on the old engine(installed in 2015) but had read about some newer pumps having a smaller bore so I stayed with the older pump.
The replacement pump on the old engine with the stock Ford 6.0 fuel line idled at 22 psi, went to 27 at 1300 and dropped from there down to 10 psi or less depending on fuel demand's, some times towing heavy loads it's dropped to 5 psi resulting in a stuck plunger in the old 160 pump, I up graded to a 215 pump on the new engine.
I plan to swap to a stronger spring in the lift pump when time allows, looking at using a Comp Cams 975-1 inner valve spring from Summit.
A fuel system write up on another forum says it will add another 30 psi of spring pressure to help eliminate plunger float at higher rpm's.
I'm not getting the low idle pecking some talk about' it's just not staying up with fuel demands at higher rpm's or under heavy load.
Some are using a 373-1 spring that increases spring pressure by 50 psi, capable of fuel pressure up to 80 psi or more.

[Ethan12v]

Wow, its been a while Between work and crappy weather i havent been able to work on the truck much but 2 things ive done since my last post.

1) I bypassed the prefilter assembly, still has a pressure drop
2) Bought a brand spankin new Tork Tek OFV and installed it, still has a pressure drop

I dont have a clue whats happening and no matter how much i cant stand throwing parts at a problem, thats pretty much the point im at. Im going to try the comp cams spring as Destroked 450 suggested